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Difficulty: EasyFormulating a Differential Diagnosis

A 22-year-old male college student presents to the student health clinic with a 2-day history of a severe sore throat, fever of 38.8°C (101.8°F), and profound fatigue. Physical examination reveals bilateral tonsillar exudates, tender posterior cervical lymphadenopathy, and a palpable spleen tip. Arrange the following conditions in order from the most likely to the least likely diagnosis based on this patient's clinical presentation.

  1. 1Infectious mononucleosis
  2. 2Group A streptococcal pharyngitis
  3. 3Acute HIV infection
  4. 4Allergic rhinitis

Answer

The correct order from most likely to least likely is: Infectious mononucleosis, Group A streptococcal pharyngitis, Acute HIV infection, and Allergic rhinitis.
The correct sequence prioritizes the diagnoses based on how completely they account for the patient's full clinical picture. Infectious mononucleosis perfectly explains the exudates, posterior cervical lymphadenopathy, and splenomegaly. Group A streptococcus is a common cause of exudative pharyngitis but lacks splenomegaly. Acute HIV can mimic infectious mononucleosis but rarely presents with tonsillar exudates. Allergic rhinitis is entirely inconsistent with the severe systemic infectious signs.

Step-by-Step Solution

1
Evaluate the patient's full clinical presentation.
The key findings are fever, severe fatigue, exudative pharyngitis, posterior cervical lymphadenopathy, and splenomegaly.
Identifying all positive physical exam findings is essential for narrowing down the differential diagnosis.
2
Identify the highest probability match for the complete symptom cluster.
Infectious mononucleosis perfectly matches all symptoms and signs, particularly the combination of posterior cervical adenopathy and splenomegaly.
Splenomegaly and posterior cervical lymphadenopathy are classic distinguishing features of Epstein-Barr virus infection.
3
Evaluate alternative infectious etiologies for partial matches.
Group A streptococcus causes exudative pharyngitis but typically involves anterior cervical nodes and lacks splenomegaly. Acute HIV causes a viral prodrome but usually lacks tonsillar exudates.
Understanding the subtle differences in presentation (anterior vs. posterior nodes, presence of exudates) helps prioritize the remaining infectious differentials.
4
Rule out non-infectious causes.
Allergic rhinitis cannot explain the fever, tonsillar exudates, or splenomegaly.
Non-infectious and benign conditions should be placed at the bottom of the differential when systemic infectious signs are prominent.

Key Concept

Differentiating common causes of acute pharyngitis and lymphadenopathy based on specific clinical signs.
Estimated Time:1m 0s
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Topics

Formulating a Differential Diagnosis

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