Diagnosis of diphtheria

First stage of diagnostics: anamnesis collection and symptom identification

The initial stage of diagnostic search aims to analyze complaints, symptom dynamics, and epidemiological data.

Assessment of the clinical picture depends on the form of the disease:

• Toxic pharyngeal diphtheria: manifests acutely with fever, pain upon swallowing, neck edema, and enlargement of submandibular lymph nodes. At the height of the disease, flaccid cranial nerve paresis (nasal voice, swallowing disorders, fluid regurgitation through the nose) and signs of myocardial involvement (tachycardia, heart rhythm irregularities) may develop.
• Laryngeal diphtheria (croup): manifests with persistent hoarseness, a dry "barking" cough, and escalating attacks of suffocation with inspiratory dyspnea.

A pathognomonic sign of diphtheria is the persistence of local pharyngeal lesions and progressive general weakness even after body temperature has returned to normal.

When collecting epidemiological history, attention is paid to contacts with patients or bacterial carriers, vaccination status, and transmission factors (e.g., consumption of unpasteurized milk). Risk groups for severe disease include immunosuppressed patients, homeless individuals, those suffering from alcoholism, and chronic pathology patients.

Assessment of local status: diphtheritic plaque

The leading objective sign upon examination of the pharynx is specific tonsillitis. The tonsils are enlarged due to edema, and a fibrinous plaque forms on their surface, which can extend beyond the lymphoid tissue.

The characteristics of the plaque change over time:

1. In the initial period: it appears as a gel-like translucent mass (fibrin exudate), often mixed with blood-tinged fluid. If removed with a spatula, it reforms very rapidly in the same place.
2. On days 2–3: the plaque acquires a grey-white color with a "pearly sheen", rises above the mucosa ("plus tissue"), and is densely fused with underlying structures.

Specific physical properties of the formed film: upon an attempt to remove it, the mucosa bleeds; the film itself cannot be rubbed between glass slides, sinks when immersed in water, and retains its shape. An important diagnostic criterion is the onset of plaque detachment 12–24 hours after the administration of diphtheria antitoxin.

Instrumental and laboratory methods

In addition to clinical examination, complementary methods are used to confirm the diagnosis and assess the severity of the condition.

• Endoscopy: laryngoscopy and bronchoscopy are indicated when respiratory diphtheria is suspected. They allow the visualization of edema, the presence of fibrinous films on the vocal cords and in the tracheobronchial tree lumen (obstruction by casts). The diagnosis of descending croup can be suspected in the presence of severe gas exchange impairment if chest X-rays show no signs of pneumonia.
• Bacteriological method: serves as the basis for etiological diagnostics. The material (oropharyngeal swab) is cultured on tellurite media. The laboratory issues a preliminary result in 48 hours, and the final result (with evaluation of biochemical properties and pathogen toxigenicity) in 72 hours.

When establishing a diagnosis, pharyngeal lesions are differentiated from tonsillitis of other etiologies, stomatitis, and abscesses, while respiratory tract lesions are differentiated from foreign bodies and nonspecific laryngotracheitis.

Basic principles of complication therapy

When mild diphtheritic polyneuropathy develops, B-complex vitamins are sufficient. For moderate and severe forms, nonsteroidal anti-inflammatory drugs, nerve conduction enhancers (neostigmine, galantamine), and glucocorticosteroids are used. Plasmapheresis shows good efficacy. Nursing care is extremely vital to prevent pressure ulcers and aspiration; with pharyngeal paresis, the patient is switched to tube feeding, and with respiratory muscle paresis, to mechanical ventilation.

Correction of cardiovascular disorders requires strict bed rest. Nitroglycerin preparations are used, and atropine is administered to improve atrioventricular conduction. In severe cases, pacemaker installation is indicated. It is important to remember that the administration of cardiac glycosides is strictly limited, as they depress the conduction system of the myocardium.

Discharge, follow-up, and sanitation of carriers

Discharge of recovered patients from the hospital is possible only upon clinical recovery and the receipt of two negative results of bacteriological cultures from oropharyngeal swabs. Swabs are taken at a 2-day interval, but no earlier than 3 days after the complete discontinuation of antibiotics.

Follow-up observation is carried out at the infectious diseases clinic on a monthly basis. Monitoring includes examination, swab culture, complete blood and urine counts, and ECG. Patients who have suffered from moderate and severe forms are indicated for vaccination with AD-M or ADS-M preparations 6 months after recovery (revaccination 6–9 months later).

Sanitation of bacterial carriers is carried out via a 1-week course of broad-spectrum antibiotics (macrolides, tetracyclines), vitamin therapy, and local antiseptics. Outpatient treatment of healthy carriers of toxigenic strains is permitted only in closed communities of up to 300 people with 100% vaccination coverage and regular bacteriological monitoring.

Class and exam questions

What else to study on this topic

• Clinical picture and stages of diphtheritic croup
• Specific therapy: administration of diphtheria antitoxin
• Differential diagnosis of pharyngeal diphtheria and infectious mononucleosis
• Mechanism of action of diphtheria exotoxin on the nervous and cardiovascular systems

Other topics in the "Respiratory Infections" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.