MCQ – 101287

A 28-year-old woman with a history of rheumatoid arthritis on chronic corticosteroid therapy presents with fever, fatigue, and dyspnea. She reports visiting a bird sanctuary in the Mississippi River Valley two weeks ago. Chest CT reveals diffuse reticulonodular infiltrates. A bronchoalveolar lavage shows numerous small yeast forms within macrophages on PAS stain. Urine antigen test is positive for fungal polysaccharide antigen. Which of the following is the most likely diagnosis?

Correct Answer � C Explanation

– Histoplasma capsulatum is a dimorphic fungus in the Ohio & Mississippi River Valleys.
– Found in bird/bat droppings → common in bird sanctuaries & caves.
– Inhaled spores infect macrophages → convert to yeast form.
– Severe in immunocompromised patients (e.g., chronic steroid use).

Key Clinical and Diagnostic Clues:
– Exposure: Bird sanctuary in the Mississippi River Valley.
– Immunosuppression: Corticosteroids for rheumatoid arthritis.
– Symptoms: Fever, dyspnea, general malaise.
– CT Chest: Reticulonodular pattern.
– BAL: Small yeasts in macrophages (PAS or GMS stain).
– Urine antigen: High sensitivity in systemic or lung disease.

Incorrect Options:
– Pneumocystis jirovecii pneumonia: More common in HIV; shows cysts, not yeasts.
– Cryptococcosis: Primarily causes meningitis; encapsulated yeasts, not intracellular.
– Aspergillosis: CT shows halo or nodules; features hyphae, not yeasts.