Adrenal Histoplasmosis: A Rare Cause of Primary Adrenal Insufficiency in an Immunocompetent Host

Background: Adrenal histoplasmosis is an uncommon yet important cause of primary adrenal insufficiency, often misdiagnosed due to its nonspecific presentation. This case highlights the diagnostic and management challenges of adrenal histoplasmosis in an immunocompetent patient. Case Presentation: A 42-year-old immunocompetent male presented with progressive fatigue, weight loss and postural dizziness for six months. Physical examination revealed pallor, postural hypotension and a BMI of 19 kg/m². Systemic examination was unremarkable except for hypotension (132/86 mmHg with a postural drop of 32 mmHg). Laboratory investigations showed anemia (Hb 8.6 g%), hyponatremia (Na 127 mmol/L), hyperkalemia and an elevated ESR (58 mm/h). Endocrine evaluation revealed a low morning cortisol level (2.3 μg/dL) with elevated ACTH (148 pg/mL), suggestive of primary adrenal insufficiency. Imaging revealed bilateral adrenal enlargement with peripheral enhancement on Contrast-Enhanced Computed Tomography (CECT) of the abdomen. Ultrasound-guided Fine-Needle Aspiration Cytology (FNAC) of the adrenal glands demonstrated intracellular 2-3 micron spores within histiocytes and giant cells, confirming Histoplasma capsulatum infection. Culture further supported the diagnosis. The patient was treated with intravenous liposomal amphotericin B, followed by oral itraconazole, along with hydrocortisone replacement therapy. He showed significant clinical improvement with normalization of adrenal function on follow-up. Conclusion: Adrenal histoplasmosis should be considered in the differential diagnosis of primary adrenal insufficiency, even in immunocompetent patients, especially in endemic regions. Early diagnosis with FNAC and culture, along with prompt antifungal therapy, is crucial for preventing adrenal crisis and improving patient outcomes.