Assistant Professor UW - Madison Middleton, Wisconsin, United States
Disclosure(s):
Neha Bapat: No financial relationships to disclose
Background: Central nervous system (CNS) blastomycosis is a rare but potentially fatal manifestation of Blastomyces dermatitidis infection. Hypothalamic-pituitary involvement is exceptionally uncommon and may result in transient or misleading endocrine abnormalities, complicating diagnostic evaluation.
Case Presentation: A young transgender woman was referred for endocrinology evaluation prior to initiation of gender-affirming hormone therapy (GAHT) after outside laboratory testing and pituitary imaging demonstrated mild hyperprolactinemia and pituitary enlargement. Several weeks earlier, she had presented with headaches and fatigue, prompting brain MRI that revealed infundibular thickening and diffuse pituitary enlargement without a discrete adenoma. Initial endocrine evaluation showed hypogonadotropic hypogonadism, mild hyperprolactinemia, suppressed thyroid-stimulating hormone (TSH) with normal free thyroxine (T4), and undetectable cortisol. Adrenocorticotropic hormone (ACTH) stimulation testing demonstrated preserved adrenal reserve.
Following shared decision-making, GAHT was initiated. Two weeks later, the patient was hospitalized with worsening headaches and blurred vision. Imaging demonstrated obstructive hydrocephalus requiring external ventricular drain placement. Repeat MRI revealed leptomeningeal enhancement with infiltrative involvement of the pituitary gland and infundibulum. Cerebrospinal fluid analysis confirmed blastomycosis meningitis. During hospitalization, the patient developed transient partial arginine vasopressin deficiency requiring a single dose of desmopressin, which resolved spontaneously. Concern for central hypothyroidism arose due to low-normal TSH with low free T4; however, free T4 measured by equilibrium dialysis was normal. GAHT was appropriately held during acute illness, and the patient was discharged on prolonged antifungal therapy.
At outpatient endocrine follow-up while receiving antifungal treatment, pituitary function normalized, including normal morning cortisol, low-normal free T4 with normal TSH, normal insulin-like growth factor 1 (IGF-1), normal total testosterone, and appropriately elevated follicle-stimulating hormone (FSH) with undetectable estradiol, consistent with cessation of GAHT.
Conclusion: This case demonstrates CNS blastomycosis presenting with pituitary stalk dysfunction, mild hyperprolactinemia, and transient multi-axis endocrine abnormalities, with complete endocrine recovery following antifungal therapy. Infectious and infiltrative etiologies should be considered in the evaluation of pituitary enlargement and hyperprolactinemia, particularly when laboratory abnormalities are discordant or evolve over time.
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