Clinical criteria and diagnostic algorithm
The diagnosis of infectious mononucleosis is based on a step-by-step evaluation. First, the physician relies on the classic clinical presentation, which includes five main syndromes:
- General toxic phenomena (prolonged high fever, weakness, sleep disturbances).
- Bilateral tonsillitis and adenoiditis (nasal congestion, nasal voice without discharge, lymphoid tissue hyperplasia).
- Generalized lymphopoloadenopathy (enlargement of all lymph node groups from the first days of illness).
- Hepatosplenic syndrome (develops at the height of the disease; splenomegaly usually predominates).
- Specific blood changes.
In some cases, the picture is complemented by jaundice and a maculopapular rash. Symptom dynamics are distinct: intoxication and fever precede oropharyngeal changes, which peak only by the third week of the disease.
Laboratory verification of diagnosis
The basis for confirming IM is enzyme-linked immunosorbent assay (ELISA) and hemogram evaluation.
- Complete blood count (CBC): Leukocytosis with absolute lymphomonocytosis is characteristic. The diagnosis is confirmed if atypical mononuclear cells (wide-cytoplasm basophilic lymphocytes) are detected in the blood. Their count must be at least 10–12% of the total mononuclear cells.
- Serological profiles (ELISA):
- anti-EBV EA-IgG (to early antigen): appear in the acute period (peak and early convalescence) in 70% of patients and disappear rapidly. This is a test for early diagnosis.
- anti-EBNA IgG (to nuclear antigen): a marker of a past infection. Absent in the acute phase, they rise during recovery and persist for life.
- anti-VCA IgG: high titers may indicate an association with Burkitt lymphoma or nasopharyngeal carcinoma.
- PCR diagnostics: Detects Epstein-Barr virus (EBV) DNA in blood, urine, CSF, or oropharyngeal swabs. The method confirms active replication, but serology is mandatory for staging the infection.
- Heterophile antibody tests: The Paul-Bunnell and Davidsohn (or Hoff-Bauer) tests are also used as part of the comprehensive workup.
Supplementary investigations
Additional methods help rule out similar infections and assess the risk of complications:
- Bacteriological culture: Oropharyngeal swabs are taken to rule out diphtheria and diagnose secondary bacterial coinfections.
- Blood biochemistry: Monitoring bilirubin, ALT, AST, and LDH levels is essential for the timely diagnosis of viral hepatitis.
- HIV testing: Acute HIV infection can present under the mask of a mononucleosis-like syndrome. HIV ELISA is prescribed three times: in the acute period, and then at 3 and 6 months.
Differential diagnosis
The direction of differential diagnosis depends on the period of the disease and the leading syndrome.
In the initial period, IM is differentiated from influenza, ARVI, measles, and rubella. In the peak period (with necrotic changes in the throat), it is differentiated from diphtheria and bacterial ("vulgar") tonsillitis.
Differences between IM and streptococcal/staphylococcal tonsillitis:
- In tonsillitis, the level of intoxication strictly correlates with oropharyngeal and regional (submandibular) lymph node involvement. In IM, it does not.
- Lymphadenitis in tonsillitis is accompanied by periadenitis; the nodes are sharply painful, and the skin over them is hyperemic.
- Bacterial tonsillitis is not characterized by polylymphadenopathy or hepatosplenomegaly.
- Blood tests in tonsillitis show neutrophilic leukocytosis with a stab shift, rather than lymphomonocytosis.
In persistent generalized lymphadenopathy, Hodgkin lymphoma must be ruled out. Unlike IM, in Hodgkin lymphoma the nodes are painless, do not respond to antibiotics, mediastinal lymph nodes are frequently affected (causing cough and dyspnea), and progressive weight loss is present. The gold standard for diagnosing Hodgkin lymphoma is a biopsy looking for Reed-Sternberg cells.
Briefly: answers to topical questions
What specific changes in blood biochemical parameters are typical for the peak of infectious mononucleosis?
Sources explicitly state that blood biochemistry in infectious mononucleosis is performed to diagnose the development of hepatitis. The following are determined:
- aminotransferase activity: ALT and AST; an IM clinical example cites their elevation as cytolytic syndrome;
- bilirubin level;
- lactate dehydrogenase (LDH) activity.
The direction of changes in bilirubin and LDH is not specified in the sources.
Class and exam questions
Why are aminopenicillins contraindicated when mononucleosis is suspected?
Drugs of this group (ampicillin, amoxicillin) cause polyclonal activation of the immune system, leading to severe toxic-allergic reactions presenting as an extensive rash.
Which antibodies confirm that a person has already had infectious mononucleosis?
The marker of a past infection is antibodies to the nuclear antigen — anti-EBNA IgG. They appear during recovery and persist in the blood for many years.
How long should physical activity restriction last after discharge?
A sparing regimen with restricted physical activity lasts up to 3 months. This is strictly necessary to prevent a life-threatening complication: splenic capsule rupture.
What else to study on this topic
- Principles of IM therapy: when glucocorticosteroid administration is justified.
- Acute mononucleosis-like syndrome: clinical presentation in CMV, HIV, and toxoplasmosis.
- Limitations of local therapy: why compresses and physiotherapy on lymph nodes are prohibited.
- Indications for dispensary follow-up and hematologist consultation after IM.
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