SUN-427 An Unusual Presentation of Histoplasmosis: Bilateral Adrenal Masses and Hypercalcemia

Abstract Disclosure: K. Khoshbin: None. K. Lane: None. S.S. Kim: None. With the increasing use of medical imaging, bilateral adrenal masses are identified more frequently. The clinical context significantly influences the likelihood of the underlying etiology found. Hypercalcemia can arise from various causes and may be an important diagnostic clue. We present the case of a 77-year-old man with no prior history of malignancy or known immune-compromising condition who was admitted to the hospital with progressive dyspnea, weight loss (40 lbs), and poor appetite over the last 4 months. Initial laboratory evaluation revealed hypercalcemia with a corrected calcium level of 12.1 mg/dL (normal range: 8.6-10.4 mg/dL) and acute kidney injury (AKI). An ultrasound performed during the workup for AKI identified bilateral adrenal masses. An MRI demonstrated large, bilateral heterogeneous masses, measuring up to 6 cm in craniocaudal dimension. The top differential diagnoses included metastases and pheochromocytomas. Biochemical workup revealed a normal 25-hydroxy vitamin D, a suppressed parathyroid hormone (PTH) level of 12 pg/mL (normal range: 11-51 pg/mL), elevated 1,25-dihydroxy vitamin D at 103 pg/mL (normal range: 19.9-79.3 pg/mL), and mildly elevated PTH-related peptide at 2.4 pmol/L (normal range: 0-2.3 pmol/L). Serum and urine metanephrines and normetanephrines were normal, as were cortisol, ACTH, renin, and aldosterone levels, ruling out pheochromocytoma and primary hyperaldosteronism. A CT scan of the chest revealed bilateral apical fibronodular scarring consistent with prior granulomatous disease, even though the patient had no known prior diagnosis. A PET scan demonstrated intensely FDG-avid, peripherally enhancing bilateral adrenal masses without evidence of an extra-adrenal primary neoplastic process. Flow cytometry excluded leukemia and lymphoma. Infectious disease testing, including endemic mycoses and tuberculosis, was initiated. Following the exclusion of pheochromocytoma, an adrenal biopsy was performed. Both the biopsy and serological studies confirmed Histoplasma capsulatum as the underlying cause. Isavuconazole was commenced for treatment. The patient had spent significant time in Chicago in his 20s, which might have been associated with Histoplasma capsulatum infection. Hypercalcemia was initially managed by intravenous fluids and denosumab but ultimately resolved 1 week after isavuconazole was started. This case highlights the importance of considering infectious diseases in the differential diagnosis of bilateral adrenal masses. It also underscores the diagnostic interplay between hypercalcemia and adrenal pathology, where both malignancy and infectious etiologies can present with overlapping features. Early identification and targeted investigations are crucial to distinguish between these conditions, ensuring timely and appropriate management. Presentation: Sunday, July 13, 2025