FRI326 Hypophysitis: A Formidable Diagnostic Challenge

Disclosure: S. Pandey: None. C. Houston: None. Background: Hypophysitis, defined as inflammation of the pituitary gland, may pose a formidable diagnostic challenge due to its protean clinical manifestations and growing spectrum of potential causes. We present a case of a young man with presumed hypophysitis in whom the etiology remains unknown. Case Summary: A previously healthy 20-year-old male with bilateral gynecomastia was referred to the endocrinology clinic. He reported a 1-year history of worsening fatigue, weight gain, intermittent headaches, bilateral breast enlargement, lack of morning erections, polydipsia, and polyuria. His childhood growth and pubertal development were reportedly normal. He denied prior head or testicular trauma, major systemic illnesses, and chronic opiate or glucocorticoid use. His physical exam was remarkable only for scant facial hair and bilateral nontender gynecomastia. His visual fields were normal, and sense of smell was intact. Laboratory evaluation at 8am revealed low total and free testosterone of 32 ng/dL (240-950) and 0.98 ng/dL (5.25-20.7), respectively, with LH of 1.4 mIU/mL (1.0-12.0) and FSH of 1.9 mIU/mL (1.0-12.0). Free T4, prolactin, IGF-1, and serum sodium were all within normal ranges. Serum cortisol was modestly elevated at 22.3 ug/dL (3.7-19.4) with normal ACTH of 49 pg/mL (7.2-63.0). Pituitary MRI showed diffuse thickening and enhancement of the pituitary stalk, compatible with infundibular hypophysitis, without evidence of mass effect upon the native gland or surrounding structures. Additional testing showed normal levels of serum calcium, iron, ferritin, ESR, and antinuclear antibodies. After overnight water deprivation, his serum sodium was elevated at 156 mmol/L (134-144) with low urine osmolality of 121 mOsmol/kg (300-900). He was started on desmopressin and testosterone, and close clinical monitoring was enacted. Conclusion: The diagnosis of hypophysitis poses multiple challenges. Its clinical manifestations can vary widely, including symptoms related to mass effect and/or symptoms of pituitary dysfunction. Diagnosis is often presumptive based on history and exam, biochemical evaluation, and neuroimaging. The spectrum of potential causes is broad and growing, including infiltrative, infectious, neoplastic, immunoglobulin G4-related, immunotherapy-induced, other autoimmune, and paraneoplastic causes. It is often a humbling experience for clinicians to narrow this exhaustive differential. Pituitary biopsy is the gold standard for diagnosis but poses significant risks, so is reserved for cases when the diagnosis remains uncertain or malignancy is suspected. Close clinical monitoring and re-evaluation is an acceptable alternative in select cases. Presentation: Friday, June 16, 2023