Differential Diagnosis for a 12-year-old with Positive Heterophile Antibodies and Splenomegaly

• Single most likely diagnosis:

  • Infectious Mononucleosis (IMN): This is the most likely diagnosis given the positive heterophile antibodies, which are a hallmark of IMN caused by Epstein-Barr virus (EBV). The splenomegaly (enlarged spleen) with a size of 11.7 cm and the presence of a likely granuloma are consistent with this diagnosis, as IMN can cause spleen enlargement and sometimes spleen abnormalities.

• Other Likely diagnoses:

  • Toxoplasmosis: Although less common, toxoplasmosis can also cause positive heterophile antibodies and splenomegaly. It's an infection caused by the parasite Toxoplasma gondii.
  • Cytomegalovirus (CMV) Infection: CMV can cause a mononucleosis-like syndrome with splenomegaly, although heterophile antibodies are typically negative. However, some cases might have atypical presentations.
  • Acute Lymphoblastic Leukemia (ALL): While not directly related to heterophile antibodies, ALL can cause splenomegaly and should be considered in the differential diagnosis of a child with an enlarged spleen.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):

  • Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with splenomegaly and might have atypical antibody responses. Missing this diagnosis could be fatal due to the aggressive nature of these cancers.
  • Sickle Cell Disease with Sepsis: Although the presence of heterophile antibodies is not typical, sickle cell disease can cause splenomegaly and is a life-threatening condition if not properly managed, especially during crises or with superimposed infections.
  • Tuberculosis: While less common in some regions, tuberculosis (TB) can cause splenomegaly and granulomas. It's crucial to consider TB, especially in areas where it's prevalent, due to its potential severity and the need for specific treatment.

• Rare diagnoses:

  • Brucellosis: A zoonotic infection that can cause splenomegaly and might have positive heterophile antibodies in some cases. It's rare but should be considered in individuals with exposure to animals or unpasteurized dairy products.
  • Cat-Scratch Disease: Caused by Bartonella henselae, this disease can lead to splenomegaly and lymphadenopathy, although it's less commonly associated with positive heterophile antibodies.
  • Histoplasmosis: A fungal infection that can cause splenomegaly and granulomas, especially in immunocompromised individuals or those exposed to bird or bat droppings.