Differential Diagnosis for Mononucleosis

Given the context of considering mononucleosis based on provided labs, the differential diagnosis can be organized into the following categories:

• Single Most Likely Diagnosis

  • Mononucleosis: This is the condition being considered based on the question, likely due to the presence of specific lab results such as atypical lymphocytosis, positive monospot test, or elevated IgM antibodies against Epstein-Barr virus (EBV), which are common indicators of infectious mononucleosis.

• Other Likely Diagnoses

  • Viral hepatitis: Can present with similar symptoms such as fatigue, loss of appetite, and can have abnormal liver function tests, which might be seen in mononucleosis as well.
  • Cytomegalovirus (CMV) infection: Similar to EBV, CMV can cause a mononucleosis-like syndrome, especially in immunocompromised individuals.
  • Toxoplasmosis: Although less common, toxoplasmosis can mimic mononucleosis, particularly in individuals with exposure to cats or undercooked meat.

• Do Not Miss Diagnoses

  • Acute lymphoblastic leukemia (ALL): A critical diagnosis not to miss, as it can present with lymphocytosis and may be confused with infectious mononucleosis. Prompt diagnosis is essential for treatment.
  • Lymphoma: Certain types of lymphoma can present with systemic symptoms and abnormal lymphocyte counts, making it crucial to differentiate from infectious causes.
  • HIV infection: Acute HIV infection can mimic mononucleosis, with symptoms such as fever, rash, and lymphadenopathy. Missing this diagnosis could lead to delayed antiretroviral therapy.

• Rare Diagnoses

  • Human herpesvirus 6 (HHV-6) infection: While common in childhood, reactivation in adults can cause a mononucleosis-like illness, particularly in immunocompromised patients.
  • Adenovirus infection: Certain serotypes can cause a syndrome similar to mononucleosis, though this is less common.
  • Brucellosis: A zoonotic infection that can present with systemic symptoms including fever, fatigue, and lymphadenopathy, potentially mimicking mononucleosis in endemic areas or in individuals with occupational exposure.