SAT-483 Hidden Valley Fever: A Case of Isolated Adrenal Coccidioidomycosis

Abstract Disclosure: Z. Najeeb: None. M. Kaur: None. P. Ginier: None. Adrenal incidentalomas require thorough evaluation to assess the risk of malignancy and hormonal hypersecretion. The Endocrine Society guidelines recommend adrenal biopsy when: (1) the lesion is hormonally inactive, (2) imaging is not clearly benign, and (3) biopsy findings are expected to alter management. While malignancy and functional adenomas are common, infectious causes are rare but possible. Coccidioides species, endemic to the Southwestern United States, cause disseminated disease in about 1% of cases, which can involve the adrenal glands and mimic malignancy.A 75-year-old male with atrial fibrillation, hyperlipidemia, and chronic kidney disease stage 3B was referred for evaluation of a left adrenal incidentaloma. His history was notable for residence in an endemic region (Central Valley, CA), 40-lb unintentional weight loss, chronic night sweats, and extensive travel to Costa Rica, Turks and Caicos, Mexico, Fiji, Honduras, Mediterranean countries, and Alaska. Imaging revealed a 4.0 x 2.5 cm adrenal lesion with 39 Hounsfield units (HU). PET/CT demonstrated hypermetabolic bilateral adrenal thickening and a left adrenal nodule (SUVmax 11.4). Hormonal testing revealed normal-range catecholamines, aldosterone, renin, and a negative Cushing’s screen. An 8 AM cortisol of 11.4 µg/dL (ref 5-25) and ACTH of 24 pg/mL (ref 6-50) suggested a low likelihood of adrenal insufficiency.A CT-guided biopsy revealed necrotic tissue with histiocytes containing intracytoplasmic fungal spherules. Serology for Coccidioides was repeatedly negative (IgM/IgG, complement fixation, and immunodiffusion). Histoplasma serology was partially reactive, with a positive yeast-phase antibody titer of 1:32 (ref <1:8) and a positive M band, but negative mycelial-phase antibody and negative urine antigen. Serology for Blastomyces and Cryptococcus included negative urine and serum antigen tests, respectively. While histoplasmosis was considered, the patient’s geographic exposure and histopathologic findings were more consistent with Coccidioides, which can exhibit false-negative serology. An infectious disease specialist was consulted and initiated fluconazole 400 mg daily. After 10 months of therapy, a follow-up MRI showed a reduction in the adrenal mass to 2.8 cm, indicating treatment response.This case highlights the importance of considering rare fungal infections in the evaluation of adrenal masses, particularly in endemic regions. Multidisciplinary collaboration was essential in avoiding unnecessary adrenalectomy. While the patient does not currently require glucocorticoid replacement, ongoing monitoring is necessary given the potential for long-term adrenal insufficiency due to progressive glandular destruction. Presentation: Saturday, July 12, 2025