Autoimmune hypophysitis associated with rheumatoid arthritis: Histopathological insights from a rare biopsy-proven case.

Background: Autoimmune hypophysitis (AH), an uncommon inflammatory disorder of the pituitary gland, involves immune cell infiltration into pituitary tissue and often occurs concurrently with systemic autoimmune diseases. Although Hashimoto's thyroiditis, systemic lupus erythematosus, and IgG4-related disease have been associated with AH, rheumatoid arthritis (RA)-associated AH remains exceedingly rare, particularly in seropositive cases. Clinical and imaging characteristics of AH mimic a wide range of infectious, neoplastic, and infiltrative pathologies. Biopsy remains the gold standard for definitive diagnosis, though it is rarely pursued. Methods: A retrospective chart review was performed to obtain the details regarding patient history, histopathological findings, and treatment course. Results: This rare case of biopsy-proven AH involved a 46-year-old female with seropositive RA. The patient presented with progressive headaches, small scotomas in both visual fields, and multiple endocrinopathies including central hypothyroidism and adrenal insufficiency. Magnetic resonance imaging revealed an infiltrative, contrast-enhancing suprasellar lesion. Surgical intervention was pursued for biopsy and debulking. Histopathology demonstrated pituitary tissue infiltrated by a heterogeneous population of inflammatory cells without evidence of well-formed granulomas. In the context of positive rheumatoid factor (RF) and anticyclic citrullinated peptide antibodies, the diagnosis of RA-associated AH was favored. The patient was treated with azathioprine with resolution of her headaches and scotomas and radiographic improvement. To our knowledge, this case represents the first biopsy-proven example of seropositive RA-associated AH. Conclusion: This case underscores the importance of maintaining a broad differential diagnosis when evaluating pituitary lesions, especially in patients with systemic autoimmune disorders, and highlights the role of tissue diagnosis and decompression in a symptomatic patient with a suprasellar lesion resulting in mass effect.