Differential Diagnosis

The patient's presentation is complex, with a variety of symptoms and laboratory findings that could suggest several different conditions. Here's a breakdown of potential diagnoses into categories:

• Single Most Likely Diagnosis

  • Infectious Mononucleosis (IMN) or Chronic Active Epstein-Barr Virus (EBV) Infection: The high EBV viral capsid antigen IgG, fluctuating liver enzymes (AST, ALT, alkaline phosphatase), and the presence of reactive lymphocytes are highly suggestive of an EBV infection. The fluctuating white and red blood cell counts, along with off-and-on high urine protein, could be related to the immune system's response to the infection. Heart enlargement and sinus tachycardia might also be seen in the context of severe or prolonged infection.

• Other Likely Diagnoses

  • Autoimmune Hepatitis: The fluctuating liver enzymes and the presence of high alkaline phosphatase could suggest autoimmune hepatitis, especially if there are autoimmune antibodies present (not mentioned but could be part of the diagnostic workup).
  • Systemic Lupus Erythematosus (SLE): SLE can cause a wide range of symptoms including kidney issues (proteinuria), heart enlargement, fluctuating blood counts, and could potentially explain the sinus tachycardia and mediastinal mass if it's related to a lupus pneumonitis or pericarditis.
  • Lymphoma: Given the mediastinal mass and the reactive lymphocytes, lymphoma should be considered, especially if the EBV infection is chronic and leading to lymphoproliferative disorders.

• Do Not Miss Diagnoses

  • Hodgkin Lymphoma: This is particularly relevant given the mediastinal mass and the EBV association. A significant proportion of Hodgkin lymphoma cases are associated with EBV.
  • Posterior Reversible Encephalopathy Syndrome (PRES) or Other Neurological Conditions: Although not directly suggested by the provided symptoms, the fluctuating blood pressure could potentially lead to neurological complications that would be critical to identify early.
  • Sarcoidosis: This condition can cause a wide range of symptoms including lymphadenopathy (which could explain the mediastinal mass), liver enzyme elevations, and could potentially affect the heart and kidneys.

• Rare Diagnoses

  • Multicentric Castleman Disease: This rare disorder can present with lymphadenopathy, hepatosplenomegaly, and could potentially explain some of the laboratory abnormalities and the mediastinal mass.
  • Kawasaki Disease: Although more common in children, it could potentially present in adults with fewer typical symptoms, leading to a delay in diagnosis. It involves inflammation of blood vessels and could explain some of the cardiac and systemic findings.
  • Primary Biliary Cholangitis (PBC) or Primary Sclerosing Cholangitis (PSC): These autoimmune liver diseases could explain the liver enzyme abnormalities but would typically have more specific diagnostic markers and might not fully account for all the systemic symptoms.