MON-064 - Inflammatory Hypophysitis Mimicking Pituitary Macroadenoma in A Patient with Rheumatoid Arthritis

Background: Sellar masses are most commonly pituitary adenomas; however, inflammatory hypophysitis is an alternative diagnosis that can present with similar clinical, biochemical, and radiographic features and may be accompanied by hypopituitarism and systemic symptoms. Autoimmune hypophysitis is uncommon and has been associated with systemic autoimmune diseases, including rheumatoid arthritis (RA). Distinguishing inflammatory hypophysitis from pituitary adenoma is important, as management and outcomes differ.
Clinical

Case: A 77-year-old woman with long-standing RA presented with progressive daily headaches and fatigue. She initially experienced partial improvement with an empiric outpatient methylprednisolone taper. Worsening symptoms prompted emergency department evaluation, where her headache responded promptly to intravenous dexamethasone. Pituitary MRI demonstrated an approximately 11 × 11 mm hypoenhancing sellar lesion initially interpreted as a pituitary macroadenoma, with superior displacement of the infundibulum and impression upon the right optic nerve. There was no evidence of hemorrhage or cavernous sinus involvement. Subsequent endocrine evaluation revealed mild hyperprolactinemia (PRL 53 ng/mL), consistent with pituitary stalk effect, along with hypopituitarism, including central hypothyroidism (TSH 0.16 mIU/L, free T4 0.5 ng/dL), secondary adrenal insufficiency (morning cortisol 1.4–1.7 µg/dL with ACTH 9 pg/mL), and hypogonadotropic hypogonadism (LH 0.6 mIU/mL, estradiol < 5 pg/mL). The patient was placed on physiologic hormone replacement, resulting in complete resolution of headaches and improvement in fatigue. Follow-up MRI demonstrated interval enlargement of the sellar lesion, prompting transsphenoidal surgery, after which she required continued hormone replacement postoperatively. Histopathology demonstrated dense fibrous tissue with acute and chronic inflammation involving the pituitary gland and adjacent dura. A mixed inflammatory infiltrate of lymphocytes, plasma cells, and macrophages was present, with granulomatous features but without well-formed granulomas or giant cells. No pituitary adenoma or infectious process was identified.
Clinical Lessons: Inflammatory hypophysitis should be considered in patients presenting with pituitary masses, hypopituitarism, and systemic symptoms, particularly in the setting of autoimmune disease. Early steroid responsiveness, pituitary stalk involvement, and biochemical features of panhypopituitarism may favor an inflammatory process rather than pituitary adenoma. In patients with systemic autoimmune disease, hypophysitis may represent a rare extra-articular manifestation, although causality cannot be definitively established. Integration of clinical presentation, endocrine evaluation, imaging, and pathology is essential to guide management.

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