MCCQE Part I medicine: infection, hematology & rheumatology questions

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The bedside qSOFA score (altered mentation, respiratory rate ≥22/min, systolic blood pressure ≤100 mmHg) identifies patients with suspected infection who are at higher risk of poor outcomes; a score of 2 or more, as seen here, should prompt further assessment for organ dysfunction. Isolated vital sign abnormalities such as fever or tachycardia alone do not define sepsis; the current Sepsis-3 definition replaced SIRS criteria because SIRS lacked specificity for identifying life-threatening organ dysfunction. Septic shock is a subset of sepsis with persistent hypotension requiring vasopressors to maintain mean arterial pressure ≥65 mmHg plus elevated lactate despite adequate fluid resuscitation.

• A. Tachycardia alone is part of SIRS criteria, which lack the specificity of Sepsis-3 criteria for identifying organ dysfunction.
• B. Radiographic or exam findings of pneumonia indicate infection source but do not by themselves define sepsis without evidence of organ dysfunction.
• D. Fever alone is a nonspecific sign of infection and does not establish organ dysfunction required for sepsis.
• E. Demographic risk factors increase susceptibility to infection but do not establish the diagnosis of sepsis.

This patient meets criteria for septic shock with hypotension, altered mentation, and elevated lactate indicating hypoperfusion. Current sepsis guidelines recommend immediate resuscitation with 30 mL/kg of balanced crystalloid within the first 3 hours, along with administration of broad-spectrum empiric antibiotics within 1 hour of recognition, since delays in antibiotic therapy are associated with increased mortality. Source control and imaging can proceed after initial stabilization. Vasopressors are added if hypotension persists despite adequate fluid resuscitation, not before fluids are given.

• B. Blood cultures should be obtained before antibiotics only if this does not significantly delay administration; empiric therapy should not be withheld pending results.
• C. Imaging is important for source identification but must not delay resuscitation and empiric antibiotics in a hemodynamically unstable patient.
• D. Vasopressors are reserved for fluid-refractory shock and should not precede an adequate fluid trial except in cases of severe cardiogenic pulmonary edema.
• E. Corticosteroids are considered only in vasopressor-refractory septic shock, not as initial empiric therapy.

Norepinephrine is the first-line vasopressor recommended for fluid-refractory septic shock because it provides potent alpha-1 mediated vasoconstriction with modest beta-1 inotropic effect, increasing mean arterial pressure with a lower arrhythmia risk compared with dopamine. The goal is to maintain a mean arterial pressure of at least 65 mmHg to ensure adequate organ perfusion. Dopamine is associated with higher rates of tachyarrhythmia and increased mortality compared with norepinephrine in septic shock trials. Hydrocortisone and additional agents such as vasopressin are reserved for shock refractory to norepinephrine at moderate to high doses.

• B. Dobutamine is an inotrope used for low cardiac output states with adequate blood pressure, not as a primary vasopressor in hypotensive shock.
• C. Hydrocortisone is reserved for shock that remains refractory despite adequate fluids and vasopressor therapy, not as an initial vasopressor substitute.
• D. Dopamine carries a higher risk of tachyarrhythmia and has been associated with increased mortality compared with norepinephrine in septic shock.
• E. Phenylephrine is a pure alpha-agonist reserved for specific situations such as tachyarrhythmia limiting other agents, not first-line therapy.

In suspected septic shock, blood cultures from two separate sites should be drawn promptly, ideally before antibiotic administration, because antibiotics rapidly reduce culture yield and cultures are essential for identifying the causative organism and tailoring de-escalation therapy. However, obtaining cultures must never meaningfully delay the administration of empiric antibiotics, which should still be given within 1 hour in septic shock. This balances the diagnostic value of cultures against the mortality risk of delayed treatment. If cultures cannot be obtained rapidly, antibiotics should proceed without waiting.

• A. A single culture set has lower sensitivity than paired cultures from separate sites and should not be delayed until after a full antibiotic course.
• B. Delaying antibiotics for culture collection beyond a short window increases mortality risk and is not recommended.
• D. Giving antibiotics first substantially lowers the yield of subsequent blood cultures, impairing pathogen identification.
• E. Blood cultures guide de-escalation and identification of resistant organisms and should still be obtained even though empiric therapy starts promptly.

Necrotizing fasciitis is suggested by pain out of proportion to visible skin findings, rapid progression, systemic toxicity with hypotension and tachycardia, skin anesthesia from nerve destruction, hemorrhagic bullae, and crepitus from gas-forming organisms tracking along fascial planes. These features distinguish it from simple cellulitis or erysipelas, which typically present with well-demarcated erythema, warmth, and tenderness proportional to the degree of inflammation, without systemic shock or skin necrosis at this stage. Diabetes is a major risk factor for necrotizing fasciitis. Recognition is critical because mortality rises substantially with delayed surgical intervention.

• A. Erysipelas presents with sharply demarcated, raised, erythematous plaques without bullae, crepitus, or anesthesia.
• B. Deep vein thrombosis causes unilateral swelling and tenderness but does not produce skin necrosis, crepitus, or systemic septic shock.
• D. A superficial ulcer infection would not explain crepitus, hemorrhagic bullae, skin anesthesia, or septic shock.
• E. Simple cellulitis causes pain proportional to erythema and warmth, without crepitus, skin necrosis, or systemic shock.

Necrotizing fasciitis is a surgical emergency, and emergent debridement of all necrotic and infected tissue is the single most important intervention to improve survival, as antibiotics alone cannot penetrate necrotic, poorly perfused tissue. Delay in surgical source control is strongly associated with increased mortality, so debridement should proceed as soon as the diagnosis is suspected or confirmed, without waiting for imaging confirmation once clinical findings are convincing. Repeat debridement is often required within 24 to 48 hours to ensure all necrotic tissue has been removed. Antibiotics and hemodynamic support are adjuncts, not substitutes, for surgical source control.

• A. Intravenous immunoglobulin has been studied as an adjunct for toxin-mediated streptococcal necrotizing infections but does not replace urgent surgical debridement.
• B. Imaging may support diagnosis in equivocal cases but should not delay surgery when clinical findings are already diagnostic.
• D. Outpatient management is inappropriate for a life-threatening necrotizing infection requiring emergent inpatient surgical intervention.
• E. Antibiotics alone cannot control necrotizing fasciitis because necrotic tissue is poorly perfused; delaying surgery increases mortality.

A synovial leukocyte count above 50,000/µL with a strong neutrophil predominance (>90%), markedly reduced synovial-to-serum glucose ratio, and absence of crystals strongly suggests bacterial septic arthritis until proven otherwise. Crystal arthropathies (gout, pseudogout) typically show characteristic crystals on polarized microscopy and lower leukocyte counts, though overlap exists. Inflammatory arthritides such as rheumatoid arthritis usually produce leukocyte counts in the 2,000-50,000/µL range with less glucose depression. Septic arthritis is a joint-threatening emergency requiring urgent joint aspiration, Gram stain, culture, and empiric antibiotics while awaiting results.

• A. Reactive arthritis typically produces a less inflammatory, sterile effusion with lower leukocyte counts.
• C. RA flares typically cause lower leukocyte counts (2,000-50,000/µL) without such profound glucose depression.
• D. Gout would show negatively birefringent needle-shaped monosodium urate crystals, which are absent here.
• E. Pseudogout would show positively birefringent rhomboid calcium pyrophosphate crystals, which are absent here.

In suspected acute hematogenous osteomyelitis, Staphylococcus aureus is the most common causative organism in children, and plain radiographs are frequently normal in the first 1-2 weeks because bony changes lag behind clinical infection. MRI is the imaging modality of choice because it has high sensitivity and specificity for detecting early marrow edema, subperiosteal abscess, and soft tissue extent, and it helps guide surgical drainage if needed. CT exposes children to ionizing radiation and is less sensitive for early marrow changes. Bone scan is sensitive but less specific and does not delineate soft tissue detail as well as MRI.

• A. Waiting 2 weeks for radiographic changes delays diagnosis and treatment of a potentially limb-threatening infection.
• C. Ultrasound can detect subperiosteal fluid collections but cannot assess marrow involvement as well as MRI.
• D. CT involves radiation exposure and is less sensitive than MRI for early marrow edema in children.
• E. Bone scan is sensitive but lacks the specificity and anatomic detail that MRI provides.

This patient has a CURB-65 score of 4 (confusion, urea elevated above 7 mmol/L, respiratory rate above 30/min, and blood pressure below 90/60 mmHg systolic or diastolic; age over 65 contributes the fifth point), indicating severe pneumonia with high mortality risk. A CURB-65 score of 3 or higher warrants hospital admission with consideration of intensive care support, since these patients have significantly elevated 30-day mortality. Scores of 0-1 support outpatient management, while a score of 2 suggests a short inpatient stay or closely supervised outpatient treatment. His hypotension and confusion additionally meet severity criteria independent of the score, reinforcing the need for inpatient, potentially critical, care.

• A. Deferring specialist assessment by a week is unsafe given his current hemodynamic instability and confusion.
• B. A CURB-65 score of 4 indicates severe pneumonia requiring hospital admission, not outpatient management.
• C. Outpatient treatment is inappropriate given his hypotension, confusion, and tachypnea indicating severe illness.
• D. A brief 6-hour observation stay is insufficient for a patient with hypotension and altered mental status from severe pneumonia.

For a previously healthy outpatient with mild community-acquired pneumonia and no comorbidities, Canadian guidelines recommend amoxicillin as first-line empiric therapy because Streptococcus pneumoniae remains the most common bacterial cause and amoxicillin provides reliable coverage with a favourable safety profile. A macrolide (such as azithromycin) is an alternative if atypical pathogens are strongly suspected or if the patient cannot tolerate amoxicillin. Respiratory fluoroquinolones are reserved for patients with comorbidities, recent antibiotic exposure, or treatment failure, to limit resistance development. Trimethoprim-sulfamethoxazole, clindamycin, and cefixime are not recommended first-line agents for typical outpatient CAP.

• A. Cefixime is not recommended as first-line therapy for outpatient CAP in a previously healthy adult.
• B. Trimethoprim-sulfamethoxazole does not reliably cover Streptococcus pneumoniae and is not first-line for CAP.
• C. Clindamycin is not a first-line agent for typical outpatient CAP and lacks reliable coverage of key pathogens.
• D. Fluoroquinolones are reserved for patients with comorbidities or treatment failure to reduce resistance pressure.

The gradual onset, prolonged dry cough, prominent headache and malaise, mild examination findings relative to diffuse bilateral interstitial infiltrates on imaging, and outbreak-like clustering in young adults living in close quarters are classic features of atypical pneumonia caused by Mycoplasma pneumoniae. Mycoplasma lacks a cell wall, so beta-lactam antibiotics are ineffective; treatment relies on macrolides, doxycycline, or respiratory fluoroquinolones. Typical bacterial pathogens such as Streptococcus pneumoniae usually cause a more acute onset with lobar consolidation and a more toxic appearance. The epidemiologic clustering among young adults in a shared living environment further supports an atypical, person-to-person transmitted pathogen.

• A. Haemophilus influenzae more commonly causes pneumonia in patients with underlying lung disease or the elderly, not healthy young adults in clusters.
• C. Streptococcus pneumoniae typically causes acute onset lobar consolidation with a more toxic clinical picture.
• D. Klebsiella pneumoniae classically causes severe lobar pneumonia with cavitation in patients with alcoholism or diabetes, not mild interstitial disease in clustered young adults.
• E. Staphylococcus aureus pneumonia is typically more severe and often follows influenza infection or occurs in IV drug users.

This patient has a Centor score of 4 (fever, tonsillar exudate, tender anterior cervical adenopathy, absence of cough), placing her in a high-probability category for group A streptococcal pharyngitis. Canadian practice recommends confirmatory testing with a rapid antigen detection test or throat culture in patients with a Centor score of 3 or higher before initiating antibiotics, to avoid unnecessary antibiotic use in those who test negative. Empiric antibiotics without testing risk overtreatment, since even high Centor scores have imperfect positive predictive value. Testing for mononucleosis or ordering a CBC is not indicated as the initial step when the clinical picture points toward streptococcal pharyngitis and point-of-care strep testing is the priority.

• A. A complete blood count does not reliably distinguish streptococcal from other causes of pharyngitis and is not the recommended next step.
• C. Mononucleosis testing is not the priority investigation when the clinical picture and Centor score point toward bacterial pharyngitis.
• D. A Centor score of 4 raises sufficient suspicion that testing, not simple reassurance, is warranted before deciding on antibiotics.
• E. Empiric antibiotics without testing are discouraged because even a Centor score of 4 does not guarantee streptococcal infection, risking antibiotic overuse.

Nitrofurantoin is a first-line agent for uncomplicated cystitis in a healthy, non-pregnant woman with normal renal function, given as 100 mg twice daily for 5 days. It concentrates in the urine with minimal systemic absorption, limiting resistance selection and systemic side effects, and local resistance rates remain low compared with trimethoprim-sulfamethoxazole in many regions. It should be avoided only in pyelonephritis (inadequate tissue levels) or significant renal impairment (creatinine clearance below 30 mL/min).

• A. Fluoroquinolones are reserved for complicated infections or when first-line agents are contraindicated, due to resistance and adverse effect concerns.
• B. This regimen and duration are excessive for uncomplicated cystitis and increase adverse effects without added benefit.
• C. Cephalexin is a second-line option, not the first-choice agent for uncomplicated cystitis.
• E. Amoxicillin has high rates of E. coli resistance and is not recommended as empiric therapy for cystitis.

Unlike in nonpregnant women, asymptomatic bacteriuria in pregnancy is treated because it is associated with an increased risk of pyelonephritis, preterm labour, and low birth weight. A single positive culture with a significant colony count (greater than or equal to 10^5 CFU/mL) is sufficient to warrant treatment with an antibiotic selected based on susceptibility and safety in pregnancy, followed by a test of cure. Screening for and treating asymptomatic bacteriuria is a standard part of routine prenatal care.

• A. Delaying treatment to repeat the culture allows ongoing risk of ascending infection and preterm complications.
• B. Asymptomatic bacteriuria in pregnancy requires treatment regardless of symptoms because of obstetric risks.
• D. Fluids and cranberry juice are not evidence-based substitutes for antibiotic treatment of bacteriuria in pregnancy.
• E. Renal imaging is not required to initiate treatment of a confirmed significant bacteriuria in pregnancy.

This patient has uncomplicated pyelonephritis with stable vital signs, no signs of sepsis, and the ability to tolerate oral intake, making her a candidate for outpatient management. A urine culture should be obtained before starting antibiotics to guide therapy and confirm the causative organism, and empiric oral antibiotics can then be started while awaiting results. Hospital admission is reserved for patients who cannot tolerate oral intake, have hemodynamic instability, signs of sepsis, pregnancy, or urinary obstruction, none of which are present here.

• B. CT imaging is not routinely required for uncomplicated pyelonephritis unless there is suspicion of obstruction or failure to improve.
• C. Urine culture should be obtained before antibiotics to confirm the organism and guide any necessary adjustment of therapy.
• D. Urology referral is reserved for suspected obstruction, abscess, or failure to respond to therapy, none of which are indicated here.
• E. Admission is unnecessary for a hemodynamically stable patient who can tolerate oral intake and has no complicating features.

Gonorrhea is a notifiable disease under provincial and territorial public health legislation across Canada, and physicians have a legal duty to report confirmed cases to the local public health authority regardless of the patient's wishes. This duty exists to enable partner notification, surveillance, and outbreak control, and it overrides routine confidentiality because the law carves out an explicit exception for reportable diseases. Patients should be informed that the report will be made, but their consent is not required for it to proceed.

• A. The duty to report to public health exists independently of whether the patient notifies partners personally.
• C. Withholding a reportable result from public health is a breach of legal obligations imposed on both laboratories and physicians.
• D. Confidentiality does not override a statutory public health reporting requirement for notifiable diseases.
• E. Reporting is mandatory at the time of diagnosis, not contingent on the development of complications.

Recent antibiotic exposure, hospitalization, and new-onset diarrhea in an older adult are classic risk factors for Clostridioides difficile infection. The most appropriate test is stool testing for C. difficile toxin (or nucleic acid amplification for the toxin gene), as this confirms active toxin-mediated disease rather than simple colonization. Stool culture for routine enteric pathogens is not useful here because it does not distinguish toxigenic C. difficile from asymptomatic carriage, and imaging or endoscopy are reserved for diagnostic uncertainty or suspected complications such as toxic megacolon.

• B. Routine stool culture does not reliably distinguish toxin-producing C. difficile from colonization and is not the test of choice here.
• C. Inflammatory markers are nonspecific and do not establish the diagnosis of C. difficile infection.
• D. CT imaging is reserved for suspected complications such as toxic megacolon or perforation, not as the initial test.
• E. Colonoscopy is invasive and reserved for diagnostic uncertainty or suspicion of other colonic pathology, not first-line testing.

Current Canadian and North American guidelines recommend oral vancomycin or oral fidaxomicin as first-line therapy for an initial episode of C. difficile infection, regardless of severity, due to superior clinical cure rates compared with metronidazole. Oral vancomycin acts locally in the colonic lumen, is poorly absorbed systemically, and achieves high fecal concentrations against C. difficile. Metronidazole has fallen out of favor as first-line therapy because of inferior cure and higher recurrence rates. Severity in this patient (WBC 13.2 x 10^9/L, creatinine not significantly elevated) is non-severe to moderate, but oral vancomycin remains preferred over metronidazole even in non-severe disease per updated guidance.

• A. Rifaximin is used for hepatic encephalopathy and traveler's diarrhea, not as primary C. difficile therapy.
• B. Intravenous metronidazole is reserved for severe, complicated disease with ileus, not initial therapy.
• D. Piperacillin-tazobactam is a broad-spectrum antibiotic that can precipitate C. difficile infection, not treat it.
• E. Metronidazole is no longer first-line due to inferior cure rates compared to vancomycin.

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of traveler's diarrhea worldwide, particularly in travelers to Latin America, Africa, and Asia. Most cases are mild and self-limited, managed supportively with oral rehydration solution; loperamide can be used safely in afebrile, non-bloody diarrhea to reduce stool frequency and improve comfort. Antibiotics are reserved for moderate-to-severe cases or when symptoms are prolonged or systemic. The absence of blood, mucus, or high fever makes invasive pathogens like Shigella or amoebiasis less likely.

• A. Entamoeba histolytica typically causes bloody diarrhea (amoebic dysentery) with a more indolent course, not watery diarrhea.
• B. Giardia classically causes greasy, foul-smelling diarrhea with bloating, often after freshwater exposure, and has a longer incubation.
• C. Vibrio cholerae causes profuse watery "rice-water" diarrhea leading to severe dehydration, which is not described here.
• E. Salmonella typhi causes enteric fever with sustained fever, relative bradycardia, and constipation more than acute watery diarrhea.

A positive HBsAg combined with a positive anti-HBc IgM indicates acute hepatitis B infection, as IgM anti-HBc typically appears early and persists for approximately 6 months before being replaced by IgG anti-HBc in chronic or resolved infection. The positive HBeAg indicates active viral replication and high infectivity. Chronic infection is characterized by HBsAg positivity persisting beyond 6 months, typically with anti-HBc IgG rather than IgM. Vaccination produces isolated anti-HBs positivity without HBsAg or anti-HBc.

• B. Chronic infection would show anti-HBc IgG positive (not IgM) with HBsAg persisting beyond 6 months.
• C. The window period shows anti-HBc IgM positive but HBsAg negative and anti-HBs not yet positive.
• D. Vaccination produces isolated anti-HBs positivity without HBsAg or anti-HBc antibodies.
• E. Resolved infection shows anti-HBs positive and anti-HBc IgG positive, with HBsAg negative.

In adults over 50 years of age with suspected bacterial meningitis, empiric therapy must cover Streptococcus pneumoniae, Neisseria meningitidis, and Listeria monocytogenes, which has increased incidence with advancing age and conditions like alcohol use disorder causing relative immune impairment. Vancomycin covers resistant pneumococcus, ceftriaxone covers pneumococcus and meningococcus, and ampicillin provides essential Listeria coverage, which cephalosporins do not reliably treat. Omitting ampicillin in this age group risks missed treatment of Listeria meningitis, which carries high mortality if untreated. Dexamethasone should also be administered with the first antibiotic dose, ideally for suspected pneumococcal meningitis.

• A. This omits ampicillin, leaving no coverage for Listeria monocytogenes, which is a concern in this age group.
• B. This omits vancomycin, leaving inadequate coverage for cephalosporin-resistant Streptococcus pneumoniae.
• C. Ampicillin and gentamicin together do not adequately cover Streptococcus pneumoniae or Neisseria meningitidis.
• D. Ceftriaxone alone does not cover Listeria monocytogenes or resistant pneumococcal strains.

Tuberculous meningitis classically presents subacutely over days to weeks with a lymphocyte-predominant pleocytosis, markedly elevated protein, and low glucose due to impaired glucose transport across the inflamed meninges, matching this patient's CSF profile and risk factor of prior residence in a high-prevalence region. Acute bacterial meningitis typically shows a neutrophil-predominant pleocytosis with a more fulminant onset within hours to a day or two. Viral meningitis usually shows lymphocytic pleocytosis but with normal or only mildly elevated protein and normal glucose. The combination of subacute course, lymphocytic predominance, high protein, and low glucose strongly favors tuberculous meningitis over these alternatives.

• A. Cryptococcal meningitis is more classically associated with immunocompromised patients (e.g., HIV) and typically requires cryptococcal antigen testing for confirmation; the clinical risk factor here points to tuberculosis.
• B. Viral meningitis usually shows normal CSF glucose and only mildly elevated protein, unlike the markedly low glucose and high protein seen here.
• D. Bacterial meningitis typically shows neutrophil predominance and a more acute onset over hours, not a 3-week subacute course.
• E. Normal pressure hydrocephalus presents with gait disturbance, urinary incontinence, and dementia without fever or CSF pleocytosis.

Canadian guidelines (including those endorsed by the Public Health Agency of Canada and provincial colleges) require informed consent for HIV testing, which can be verbal, after providing basic pre-test information (purpose of the test, meaning of possible results, and confidentiality). Written consent specific to HIV is not mandatory in most jurisdictions, and opt-out testing without discussion does not meet the informed consent standard. Routine or risk-based offer of testing is encouraged regardless of reported risk factors, since many at-risk patients do not disclose or recognize risk. Employers must never be informed of HIV testing or results without separate explicit patient authorization.

• A. Written consent specific to HIV testing is not required in current Canadian guidelines; verbal informed consent suffices.
• B. Testing should not be withheld pending a specific risk factor, since routine offer improves early diagnosis.
• C. Disclosing testing or results to an employer without explicit separate consent breaches confidentiality and privacy law.
• D. Proceeding without pre-test discussion fails the informed consent standard even if objection is theoretically possible.

The combination of fever, pharyngitis, maculopapular rash, oral ulcers, and lymphadenopathy occurring 2-4 weeks after a high-risk sexual exposure is classic for the acute retroviral syndrome of HIV seroconversion. Antibody-based rapid tests can be negative early because antibodies typically take 3-12 weeks to develop, so a negative antibody test does not exclude acute HIV infection in this window. Diagnosis in this period requires HIV RNA (viral load) testing or a fourth-generation antigen/antibody combination assay, which detects p24 antigen earlier. The other conditions can cause similar mononucleosis-like illness but do not explain a negative test obtained specifically in this exposure timeline the way the HIV antibody window period does.

• B. EBV mononucleosis can present similarly but does not explain the specific exposure history and need for confirmatory HIV RNA testing.
• C. Disseminated gonococcal infection usually causes tenosynovitis, dermatitis, and arthritis rather than pharyngitis and diffuse rash.
• D. Secondary syphilis usually occurs weeks to months after a painless chancre and does not typically cause this acute febrile pharyngitic illness.
• E. Primary CMV can mimic this illness but is less likely given the specific high-risk sexual exposure timeline provided.

Primary prophylaxis against Pneumocystis jirovecii pneumonia (PJP) is indicated when the CD4 count falls below 200 cells/microL, and trimethoprim-sulfamethoxazole is the first-line agent. This patient's CD4 count of 170 cells/microL meets that threshold. Prophylaxis can be discontinued once the CD4 count rises above 200 cells/microL for at least 3 months on effective antiretroviral therapy. MAC prophylaxis is reserved for CD4 counts below 50 cells/microL, which this patient has not reached. Fluconazole and valganciclovir prophylaxis are not routinely recommended regardless of CD4 count in current guidelines due to lack of mortality benefit and risk of resistance or toxicity.

• A. Primary CMV prophylaxis with valganciclovir is not recommended; CMV disease is managed by monitoring and treating when it occurs.
• B. MAC prophylaxis is indicated only when the CD4 count falls below 50 cells/microL, well below this patient's count.
• D. Routine primary fluconazole prophylaxis for cryptococcal disease is not recommended in current guidelines regardless of CD4 count.
• E. Isoniazid should only be started after excluding active tuberculosis and confirming latent infection with TST or IGRA.

This presentation of subacute dyspnea, dry cough, diffuse bilateral interstitial infiltrates, and hypoxemia in a patient with advanced HIV and CD4 count below 200 cells/microL is classic for Pneumocystis jirovecii pneumonia. Trimethoprim-sulfamethoxazole is first-line treatment, and intravenous administration is preferred initially in moderate to severe disease (PaO2 below 70 mmHg or alveolar-arterial gradient above 35 mmHg on room air). Adjunctive corticosteroids (oral prednisone or IV methylprednisolone) are indicated in moderate to severe PJP to reduce the inflammatory response from organism death and improve oxygenation and survival. Intravenous pentamidine and clindamycin-primaquine are reserved as second-line options for patients intolerant to or failing TMP-SMX, and oral TMP-SMX alone is used only for mild disease.

• A. Clindamycin-primaquine is an alternative regimen for TMP-SMX-intolerant patients with mild to moderate disease, not first-line for this severity.
• B. Oral therapy alone is reserved for mild PJP; this patient has moderate-severe disease with PaO2 below 70 mmHg requiring IV therapy and steroids.
• C. This antibacterial combination targets community-acquired bacterial pneumonia, not PJP, and does not match the described infiltrate pattern.
• D. Pentamidine is second-line therapy, used when TMP-SMX cannot be given, and does not address the need for adjunctive steroids.

Interferon-gamma release assays (IGRA) are preferred over the tuberculin skin test (TST) in individuals with a history of BCG vaccination, because IGRA uses antigens specific to Mycobacterium tuberculosis that are not present in the BCG vaccine strain, avoiding false-positive results from prior vaccination. TST relies on purified protein derivative, which cross-reacts with BCG and can produce a positive result unrelated to true latent TB infection. Both TST and IGRA detect latent infection, but IGRA has higher specificity in BCG-vaccinated populations, which is relevant for many immigrants to Canada. Sputum smear, culture, and CT imaging are used to investigate suspected active disease, not to screen for latent infection in an asymptomatic patient.

• B. Sputum AFB smear is used to evaluate suspected active pulmonary TB, not to screen asymptomatic patients for latent infection.
• C. Sputum culture is reserved for diagnosing active tuberculosis, not for latent infection screening in an asymptomatic patient.
• D. CT imaging is used to investigate suspected active disease or complications, not for latent TB screening.
• E. TST cross-reacts with BCG vaccination and has a higher false-positive rate in this population.

Active pulmonary tuberculosis with a positive sputum smear is highly infectious and is a legally reportable disease in every Canadian province and territory under public health legislation, overriding the usual duty of confidentiality in the interest of population health protection. Physicians are legally obligated to report suspected and confirmed active TB cases to public health authorities regardless of patient objection, and this duty does not require patient consent. Airborne precautions (negative pressure room, N95 respirator for staff) must be instituted immediately based on clinical and smear findings, without waiting for culture confirmation, since cavitary disease with positive smear indicates high infectiousness. Patient autonomy does not extend to withholding information that is legally mandated for reporting to protect public health.

• A. Informing only family members does not fulfill the legal public health reporting obligation to the designated authority.
• B. Airborne isolation must begin immediately based on clinical and smear findings, not delayed pending culture confirmation.
• C. Reporting obligations under public health law do not require patient consent and should not be delayed for consent-seeking.
• D. Reportable disease legislation legally overrides confidentiality for active TB; the physician must report and isolate despite the request.

Isoniazid causes peripheral neuropathy through interference with pyridoxine (vitamin B6) metabolism, which is why pyridoxine supplementation is often co-administered, particularly in patients at higher risk such as those with diabetes, malnutrition, or alcohol use. Ethambutol causes dose-related optic neuritis, presenting with decreased visual acuity and red-green color discrimination deficits, which requires baseline and periodic visual acuity and color vision testing during treatment. This combination of findings, stocking-distribution sensory neuropathy plus visual and color vision changes, corresponds specifically to isoniazid and ethambutol toxicity respectively. Rifampin is notable for hepatotoxicity, drug interactions via cytochrome P450 induction, and orange discoloration of body fluids, not neuropathy or visual toxicity. Pyrazinamide is associated with hepatotoxicity and hyperuricemia, not peripheral neuropathy.

• B. Ethambutol is not a typical cause of hepatotoxicity, and rifampin does not cause peripheral neuropathy.
• C. Isoniazid causes peripheral neuropathy, not optic neuritis, which is instead attributable to ethambutol.
• D. Rifampin does not cause peripheral neuropathy; it is known for hepatotoxicity and drug interactions, and pyrazinamide causes hepatotoxicity but does not explain the visual symptoms here.
• E. Pyrazinamide causes hepatotoxicity and hyperuricemia rather than peripheral neuropathy, and rifampin's hallmark effect is fluid discoloration, not a mechanism for this presentation.

When documentation of prior immunization is unavailable or unreliable, the Canadian Immunization Guide recommends treating the person as unimmunized and initiating an age-appropriate catch-up schedule rather than relying on serology, which is costly and not reliable for all antigens. Catch-up schedules allow accelerated intervals for inactivated vaccines and combine live vaccines as appropriate, without unnecessary delay. Waiting for records that may never arrive leaves the patient susceptible to preventable disease. Tetanus alone is insufficient; pertussis, diphtheria, measles-mumps-rubella, and other antigens depend on local epidemiology and risk factors.

• A. Live vaccines can be co-administered, but inactivated vaccines do not need to be deferred; delaying them provides no benefit and prolongs susceptibility.
• B. Adults require more than tetanus; diphtheria, pertussis, MMR and other antigens must also be addressed based on risk and prior history.
• C. Delaying vaccination indefinitely while awaiting records leaves the patient unnecessarily susceptible to preventable illness.
• D. Serologic testing for every antigen is impractical, costly, and not recommended as a routine screening step before catch-up vaccination.

Yellow fever vaccine is a live attenuated vaccine and is generally contraindicated in pregnancy because of a theoretical risk of transmission of the attenuated virus to the fetus. If travel to a high-risk area is unavoidable, the risks and benefits must be weighed with the patient, and a medical waiver can be considered if vaccination is deferred. Inactivated influenza vaccine is recommended in every trimester of pregnancy. Tdap, hepatitis A, and pneumococcal polysaccharide vaccines are inactivated or subunit vaccines and are considered safe to give in pregnancy when otherwise indicated.

• B. Pneumococcal polysaccharide vaccine is not a live vaccine and can be given in pregnancy if indicated.
• C. Tdap is an inactivated/acellular vaccine routinely recommended during pregnancy, typically in the third trimester.
• D. Hepatitis A vaccine is inactivated and can be given in pregnancy if indicated by exposure risk.
• E. Inactivated influenza vaccine is recommended in pregnancy and is not a live vaccine.

After first aid, a needlestick injury must be promptly reported to occupational health so that risk is assessed, baseline bloodwork (including HIV, hepatitis B, hepatitis C) is drawn from both the worker and, with consent, the source patient, and HIV post-exposure prophylaxis is started within hours if indicated, ideally within 2 hours and no later than 72 hours. This process also fulfills legal and workplace reporting obligations and protects the worker's rights to compensation if seroconversion occurs. Delaying action until source results are available risks missing the window for effective post-exposure prophylaxis. Hepatitis B immune globulin is only given based on the worker's immune status and the source's hepatitis B surface antigen status, not automatically.

• A. Failing to report formally forfeits timely risk assessment, prophylaxis, and workers' compensation protections.
• C. Hepatitis B immune globulin is given based on the worker's vaccination/immune status and the source's HBsAg status, not automatically to everyone.
• D. Testing should not be deferred until symptoms develop; prompt source testing guides the need for prophylaxis and follow-up.
• E. HIV post-exposure prophylaxis is time-sensitive and should not be delayed pending source testing, which can take time to arrange.

In an adult male with confirmed iron deficiency anemia and no obvious source of blood loss, the gastrointestinal tract is the most likely site, and current guidelines recommend bidirectional endoscopy (esophagogastroduodenoscopy and colonoscopy) to search for an occult source such as colorectal cancer, peptic ulcer disease, or angiodysplasia, regardless of the absence of gastrointestinal symptoms. Iron deficiency in a man or postmenopausal woman without an obvious cause should never be treated empirically without investigation, since this risks delaying diagnosis of a malignancy. A fecal occult blood test has limited sensitivity and does not replace endoscopic evaluation when iron deficiency anemia is already established. Celiac serology may be part of the workup but does not take priority over colorectal cancer screening via endoscopy.

• A. Celiac serology can be included in the workup but bidirectional endoscopy takes priority to exclude colorectal cancer in this age group.
• B. Starting iron empirically without investigating the cause risks missing a gastrointestinal malignancy or other serious source of blood loss.
• C. Fecal occult blood testing has low sensitivity and a negative result does not exclude a significant lesion; it should not substitute for endoscopy.
• D. B12 and folate levels do not explain microcytic iron deficiency anemia and are not the priority next step.

In anemia of chronic disease, inflammatory cytokines increase hepcidin, which traps iron within macrophages and reduces iron release to the bone marrow; this produces a low serum iron and low total iron-binding capacity, with a normal or elevated ferritin because ferritin is an acute-phase reactant reflecting iron stores rather than a low total body iron state. This pattern distinguishes it from iron deficiency anemia, where low iron stores cause both low ferritin and typically a high, not low, total iron-binding capacity. The mild normocytic to mildly microcytic anemia and underlying rheumatoid arthritis support a chronic inflammatory process rather than true iron deficiency. Thalassemia trait would show a normal or high iron panel with a disproportionately low MCV relative to the hemoglobin level.

• B. Hemolytic anemia would show elevated indirect bilirubin, elevated LDH, and reticulocytosis, not this iron study pattern.
• C. Sideroblastic anemia typically shows a normal or elevated serum iron and ferritin with ringed sideroblasts on bone marrow, not this iron-binding capacity pattern.
• D. Thalassemia trait typically shows normal iron studies and a very low MCV relative to the degree of anemia, not this pattern.
• E. True iron deficiency causes a high, not low, total iron-binding capacity, and ferritin would be low rather than elevated.

A normal RDW with a markedly low MCV and a high red cell count (Mentzer index = MCV/RBC = 68/5.8 ≈ 11.7, well below 13) is characteristic of thalassemia trait, which produces uniformly small red cells because of a fixed defect in globin chain synthesis rather than progressively worsening cell size variation. Iron deficiency anemia typically produces an elevated RDW because red cells become progressively more microcytic over time as iron stores are depleted, along with a low rather than normal ferritin. The normal ferritin in this patient argues against iron deficiency and supports a hereditary cause of microcytosis. Hemoglobin electrophoresis would confirm the diagnosis of thalassemia trait.

• A. Anemia of chronic disease is typically normocytic or mildly microcytic with a normal or elevated ferritin and low iron, not this degree of microcytosis with a normal RDW.
• C. Iron deficiency anemia usually shows an elevated RDW and a low ferritin, neither of which is present here.
• D. Sideroblastic anemia typically shows a high RDW with dimorphic red cell populations and ringed sideroblasts on bone marrow examination.
• E. Vitamin B6 deficiency can cause sideroblastic anemia but is rare and would not produce this uniform microcytosis pattern with a normal RDW.

Chronic alcohol use impairs folate absorption and hepatic storage, while a diet low in fresh vegetables and fortified grains provides inadequate folate intake, together producing megaloblastic anemia with macro-ovalocytes and hypersegmented neutrophils, a hallmark finding reflecting impaired DNA synthesis in granulocyte precursors. Vitamin B12 deficiency is excluded by the normal B12 level in this scenario. Hypothyroidism can cause mild macrocytosis but does not typically produce hypersegmented neutrophils or significant megaloblastic change. Myelodysplastic syndrome can cause macrocytic anemia but is less likely than a nutritional cause given the clear history of poor diet and alcohol use, and iron deficiency causes microcytic, not macrocytic, anemia.

• A. The normal serum B12 level excludes B12 deficiency as the cause in this patient.
• C. Myelodysplastic syndrome is less likely given the clear dietary and alcohol-related risk factors for folate deficiency.
• D. Hypothyroidism can cause mild macrocytosis but does not typically cause hypersegmented neutrophils or this degree of megaloblastic change.
• E. Iron deficiency produces microcytic, not macrocytic, anemia and does not explain hypersegmented neutrophils.

The combination of anemia, indirect hyperbilirubinemia, elevated LDH, reticulocytosis, and spherocytes without schistocytes points to extravascular hemolysis, and the direct antiglobulin test (Coombs test) detects IgG or complement bound to red cells, confirming an immune-mediated mechanism. A positive result distinguishes autoimmune hemolytic anemia from hereditary spherocytosis, which has a similar smear but a negative DAT. Haptoglobin would be low in any hemolysis and does not identify the mechanism. Osmotic fragility testing is used for hereditary spherocytosis, not to establish an immune cause. This is the pivotal test that changes management toward immunosuppressive therapy.

• A. Haptoglobin is low in hemolysis of any cause and does not distinguish immune from non-immune mechanisms.
• B. Bone marrow examination is unnecessary when peripheral findings and reticulocytosis already confirm a hemolytic process.
• D. Hemoglobin electrophoresis is used to diagnose hemoglobinopathies such as sickle cell disease or thalassemia, not autoimmune hemolysis.
• E. Osmotic fragility testing supports hereditary spherocytosis but does not confirm an immune mechanism.

G6PD deficiency impairs the hexose monophosphate shunt, reducing NADPH generation and consequently depleting reduced glutathione, the main defense against oxidative stress in red cells. Oxidant drugs such as sulfonamides, dapsone, and primaquine, as well as fava beans and infection, precipitate hemoglobin denaturation (Heinz bodies) and membrane damage, causing hemolysis seen as bite cells on smear. This X-linked disorder is more common and more severe in males, and episodes are typically triggered rather than continuous. The other mechanisms describe different hemolytic processes unrelated to oxidative stress.

• A. Antibody-mediated destruction describes autoimmune hemolytic anemia, which would show a positive direct antiglobulin test.
• C. Defective spectrin describes hereditary spherocytosis, a membrane structural defect unrelated to oxidative triggers.
• D. Mechanical shearing describes microangiopathic hemolytic anemias such as TTP or DIC, not an oxidant-triggered process.
• E. Complement-mediated hemolysis describes mechanisms like paroxysmal nocturnal hemoglobinuria or cold agglutinin disease, not G6PD deficiency.

The priority in an uncomplicated vaso-occlusive crisis is rapid, aggressive analgesia, with intravenous opioids titrated against frequent pain reassessment, alongside intravenous fluids and oxygen if hypoxic. Exchange transfusion is reserved for severe complications such as acute chest syndrome, stroke, or multiorgan failure, not routine painful crises. Hydroxyurea reduces the frequency of future crises but has no role in acute pain management. Antibiotics are not indicated without evidence of infection, and incentive spirometry is used to prevent atelectasis and acute chest syndrome but does not substitute for analgesia.

• A. Incentive spirometry helps prevent acute chest syndrome but does not address the acute pain, which is the priority here.
• B. Exchange transfusion is reserved for severe complications like acute chest syndrome or stroke, not an uncomplicated painful crisis.
• C. Hydroxyurea is a preventive agent for reducing crisis frequency, not an acute treatment for pain.
• D. Empiric antibiotics are not indicated without signs of infection such as fever with another localizing source.

Immune thrombocytopenia (ITP) remains a clinical diagnosis of exclusion, made when isolated thrombocytopenia is found with an otherwise normal blood count and peripheral smear, and no alternative cause such as medication, infection, or marrow disorder is identified clinically. Routine bone marrow biopsy is not required in typical presentations, especially in young patients with classic findings, and is reserved for atypical features or poor treatment response. Antiplatelet antibody testing lacks sufficient sensitivity and specificity to be diagnostically useful. While HIV and hepatitis C testing are reasonable in at-risk patients, they are part of the exclusion workup rather than the defining step itself, and this patient's presentation already fits the typical pattern after appropriate clinical exclusion.

• A. While viral serologies can be part of the exclusion process in appropriate patients, the diagnosis itself rests on exclusion of alternative causes, not a specific positive test.
• B. Antiplatelet antibody testing has poor sensitivity and specificity and is not used to confirm the diagnosis.
• D. Bone marrow biopsy is not routinely required in typical ITP presentations and is reserved for atypical cases or treatment failure.
• E. ADAMTS13 activity is tested when thrombotic thrombocytopenic purpura is suspected, which presents with microangiopathic hemolysis, not isolated thrombocytopenia with a normal smear.

An isolated prolonged aPTT with a normal PT and normal platelet count in a male child with a maternal family history strongly suggests hemophilia A, caused by factor VIII deficiency, inherited in an X-linked recessive pattern. Factor VIII is part of the intrinsic pathway, explaining the isolated aPTT prolongation while the extrinsic pathway-dependent PT remains normal. Hemarthrosis after minor trauma is a classic presentation of hemophilia, distinguishing it from mucocutaneous bleeding patterns seen in platelet or von Willebrand disorders. Factor VII deficiency and prothrombin (factor II) deficiency affect the extrinsic or common pathway and would prolong the PT.

• A. Factor II (prothrombin) is part of the common pathway and its deficiency would prolong both PT and aPTT.
• B. A platelet function defect would present with mucocutaneous bleeding and a normal aPTT, not isolated aPTT prolongation with hemarthrosis.
• D. Factor VII deficiency affects the extrinsic pathway and would prolong the PT, not isolate the aPTT.
• E. Von Willebrand disease typically causes mucocutaneous bleeding and may mildly prolong aPTT via low factor VIII, but the X-linked family history and hemarthrosis pattern favor hemophilia A.

Von Willebrand disease is the most common inherited bleeding disorder and typically presents with mucocutaneous bleeding such as menorrhagia and epistaxis, often with a positive family history due to autosomal dominant inheritance in most subtypes. Standard coagulation screening tests including PT, aPTT, and platelet count are frequently normal, and diagnosis requires specific assays such as von Willebrand factor antigen, activity, and factor VIII level. Hemarthrosis and deep muscle bleeding, characteristic of hemophilia, are typically absent, as in this patient. The normal platelet count argues against immune thrombocytopenia, and the clinical picture does not fit DIC.

• A. Factor XI deficiency is rare and typically presents with a prolonged aPTT, which is normal here.
• B. Immune thrombocytopenia would show a low platelet count, which is normal in this patient.
• C. Hemophilia A carriers are usually asymptomatic or have mild bleeding and the condition is X-linked, less consistent with bleeding in both mother and daughter.
• E. DIC is an acute, consumptive coagulopathy with abnormal coagulation studies and low platelets, not a chronic lifelong bleeding pattern.

Major, life-threatening bleeding on warfarin requires immediate reversal with both intravenous vitamin K, to restore hepatic synthesis of functional clotting factors, and prothrombin complex concentrate (PCC), which rapidly replenishes factors II, VII, IX, and X. PCC acts within minutes, bridging the delay of several hours before vitamin K takes effect, making the combination the standard of care for major bleeding. Vitamin K alone is too slow for an actively bleeding, hemodynamically unstable patient. Fresh frozen plasma is an alternative when PCC is unavailable but is less effective and requires larger volumes with a slower onset. Protamine sulfate reverses heparin, not warfarin.

• A. Vitamin K alone takes hours to restore factor synthesis and does not provide the immediate correction needed in major active bleeding.
• B. Protamine sulfate is the reversal agent for unfractionated heparin, not for warfarin-induced coagulopathy.
• C. Simply observing a hemodynamically unstable, actively bleeding patient on a supratherapeutic INR is inappropriate and dangerous.
• E. Fresh frozen plasma without vitamin K provides only transient factor replacement and is inferior to PCC with vitamin K for major bleeding.

Auer rods on peripheral smear are pathognomonic for myeloid blasts and strongly suggest acute myeloid leukemia, though blasts with high nuclear-to-cytoplasmic ratio and fine chromatin can also be seen in acute lymphoblastic leukemia. The combination of circulating blasts, cytopenias (anemia and thrombocytopenia), fever, bruising, and organomegaly indicates acute leukemia, which is a hematologic emergency due to risks of infection, bleeding, hyperleukocytosis, and tumor lysis syndrome. Same-day urgent referral allows rapid confirmatory bone marrow examination, cytogenetics, and initiation of treatment, which significantly affects outcomes. Any delay increases the risk of life-threatening complications such as sepsis or spontaneous hemorrhage.

• A. Bone marrow biopsy is indicated urgently, not electively, given the peripheral smear findings.
• B. This presentation is not benign and requires immediate escalation, not watchful waiting.
• C. Iron deficiency does not explain blasts with Auer rods, thrombocytopenia, and organomegaly, and delaying care is dangerous.
• E. A 2-week delay is inappropriate given the risk of sepsis, bleeding, and leukostasis in acute leukemia.

This patient has anemia, renal impairment, hypercalcemia, and an elevated total protein with normal albumin, raising strong suspicion for multiple myeloma with a monoclonal gammopathy. Serum protein electrophoresis with immunofixation is the key initial test, as it identifies and characterizes a monoclonal (M) protein spike, which is required to diagnose and classify the paraprotein. Urine dipstick is unreliable for detecting Bence Jones proteins because it primarily detects albumin, so a positive SPEP triggers further workup including serum free light chains, skeletal survey or whole-body imaging, and bone marrow biopsy. CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lesions) support the diagnosis once a monoclonal protein is confirmed.

• A. Bone scan is poor at detecting myeloma lytic lesions because they are often not osteoblastic; skeletal survey or whole-body imaging is preferred.
• B. Inflammatory markers do not help diagnose myeloma and are nonspecific.
• D. Free light chain ratio is useful but does not replace SPEP for initially characterizing and quantifying the monoclonal protein.
• E. Urine protein quantification does not specifically identify a monoclonal light chain and is not the best initial test.

Methotrexate, the first-line DMARD for rheumatoid arthritis, acts primarily by inhibiting dihydrofolate reductase, reducing folate-dependent purine and pyrimidine synthesis and exerting anti-inflammatory effects through adenosine release. Folic acid supplementation is routinely co-prescribed to reduce methotrexate-related toxicity, particularly mucositis, gastrointestinal upset, and hepatotoxicity, without reducing efficacy. Baseline and periodic monitoring includes complete blood count, liver enzymes, and renal function rather than tuberculosis screening, which is reserved for biologic agents such as TNF inhibitors. Methotrexate is typically given once weekly, and patient education on this dosing schedule is critical to avoid fatal overdose from daily dosing errors.

• A. This describes a JAK inhibitor (such as tofacitinib), not methotrexate, which is not first-line therapy.
• B. This describes tocilizumab, an IL-6 receptor antagonist, not the first-line DMARD.
• C. This describes a TNF inhibitor (such as infliximab), which is used after inadequate response to methotrexate.
• E. This describes rituximab, a B-cell depleting agent, not methotrexate.

This patient demonstrates classic features of inflammatory back pain: onset before age 40, duration greater than 3 months, insidious onset, improvement with exercise, and no improvement with rest, combined with morning stiffness lasting more than 30 minutes. Alternating buttock pain reflects sacroiliac joint involvement, and the history of acute anterior uveitis (painful red eye) is a common extra-articular manifestation of HLA-B27-associated spondyloarthropathy. The positive HLA-B27 and elevated ESR support the diagnosis of ankylosing spondylitis, and reduced lumbar flexion reflects early axial involvement. Imaging of the sacroiliac joints (X-ray or MRI) would typically follow to assess for sacroiliitis and confirm the diagnosis.

• A. Disc herniation typically causes pain that worsens with activity and may have radicular features, not this pattern of inflammatory back pain.
• B. Fibromyalgia does not cause objectively reduced spinal mobility, elevated ESR, or uveitis.
• C. Mechanical back pain typically improves with rest and worsens with activity, the opposite of this presentation.
• D. Osteoarthritis is unlikely at this age and does not explain the extra-articular eye findings or elevated inflammatory markers.

ANA is a highly sensitive but nonspecific screening test for systemic lupus erythematosus (SLE), positive in over 95% of patients but also found in other autoimmune diseases and some healthy individuals, especially at low titers. Anti-dsDNA antibodies are much more specific for SLE and, importantly, their titers often correlate with disease activity and risk of lupus nephritis, making them useful both diagnostically and for monitoring. This patient's malar rash, oral ulcers, arthritis, and proteinuria alongside positive ANA and anti-dsDNA fulfill clinical and immunologic criteria for SLE, and the proteinuria raises concern for renal involvement requiring further workup. A positive ANA alone, without additional clinical or serologic criteria, is not diagnostic because ANA positivity is common and nonspecific.

• B. This reverses the known relationship; ANA is the more sensitive but less specific test compared with anti-dsDNA.
• C. A homogeneous ANA pattern is nonspecific and is not characteristic specifically of drug-induced lupus, which is more associated with anti-histone antibodies.
• D. SLE can be diagnosed with positive ANA and other clinical/serologic criteria even without anti-dsDNA, since not all SLE patients have detectable anti-dsDNA.
• E. ANA alone is not diagnostic of SLE because it is nonspecific and can be positive in other conditions or in healthy people, especially at lower titers.

Giant cell arteritis (GCA) with visual symptoms is an ophthalmologic emergency because untreated inflammatory occlusion of the ophthalmic or posterior ciliary arteries can cause irreversible blindness within hours. High-dose glucocorticoids (intravenous methylprednisolone) should be started immediately on clinical suspicion, without waiting for temporal artery biopsy, since biopsy results remain valid for up to 2 weeks after starting steroids. Delaying treatment risks permanent vision loss, and biopsy is used to confirm the diagnosis retrospectively, not to guide the decision to treat. Low-dose steroids are inadequate when visual loss is threatened or has begun.

• A. Aspirin alone does not treat the underlying vasculitic inflammation causing ischemic optic neuropathy.
• B. Delaying treatment while awaiting biopsy risks permanent, irreversible vision loss.
• C. Low-dose steroids are insufficient when there is visual involvement; high-dose therapy is required emergently.
• E. Methotrexate has a slow onset of action and is used as a steroid-sparing adjunct, not for acute emergency treatment.

Polymyalgia rheumatica classically presents in adults over 50 years with bilateral shoulder and/or hip girdle pain and morning stiffness lasting more than 30 minutes, accompanied by markedly elevated inflammatory markers (ESR and CRP), without objective muscle weakness or significant joint swelling. Creatine kinase is normal, distinguishing it from inflammatory myopathies. The diagnosis is further supported by a rapid and dramatic clinical response to low-dose prednisone (typically 12.5–25 mg daily), often within days. Screening for coexisting giant cell arteritis symptoms (headache, jaw claudication, visual changes) is essential given their frequent overlap.

• A. Fibromyalgia causes diffuse tender points and fatigue but does not elevate ESR/CRP and does not respond to steroids.
• B. Polymyositis causes true proximal muscle weakness with elevated creatine kinase, which is absent here.
• C. Statin-induced myopathy causes weakness and elevated creatine kinase, not isolated inflammatory girdle pain with a normal CK.
• D. Rheumatoid arthritis typically involves symmetric small joint synovitis with swelling, not isolated girdle pain without joint findings.