MON-076 - Granulomatosis with Polyangiitis Presenting as Pituitary Hypophysitis Mimicking Pituitary Adenoma: A Diagnostic Challenge with Critical Therapeutic Implications

Background:

Pituitary masses are commonly attributed to adenomas. However, inflammatory etiologies such as hypophysitis must be considered, particularly in patients with systemic disease. Granulomatosis with Polyangiitis (GPA) is a rare cause of secondary hypophysitis and may closely mimic a pituitary adenoma both clinically and radiographically. Distinguishing between these entities is essential, as management strategies differ significantly.

Case Presentation:

A 62-year-old man with a history of Crohn’s disease, rheumatoid arthritis, chronic pancreatitis and vasculitis presented with progressive fatigue, weight loss, headaches and visual disturbances over several months. Pituitary MRI revealed a 1.5 cm cystic sellar mass with suprasellar extension impinging the optic chiasm and stalk thickening, initially interpreted as a macroadenoma. Laboratory evaluation demonstrated panhypopituitarism, including central adrenal insufficiency, hypothyroidism, hypogonadism, and arginine vasopressin deficiency (AVP-D). Despite hormone replacement, the patient experienced progressive clinical decline with fevers, nasal inflammation, and worsening sinus disease. Repeat imaging showed stable pituitary lesion size but evolving sinonasal pathology. Extensive infectious and autoimmune workup was initially unrevealing, including negative ANCA and IGG4 serologies. Given multisystem involvement, an inflammatory process was suspected. Definitive diagnosis was established through a lacrimal gland biopsy, confirming GPA. The pituitary lesion was subsequently reclassified as GPA-associated hypophysitis rather than adenoma. The patient was treated with high-dose glucocorticoids followed by rituximab, resulting in improvement of systemic symptoms. Hormonal deficiencies required ongoing replacement therapy. Neurosurgical intervention was avoided.


Discussion:

Pituitary involvement in GPA is rare. Radiologic features such as stalk thickening and cystic changes may overlap with adenomas, leading to diagnostic delay. Negative ANCA does not exclude GPA. This case highlights the importance of considering systemic inflammatory diseases in atypical pituitary masses, especially when accompanied by AVP-D and multisystem involvement. Early differentiation between adenoma and hypophysitis is critical, as treatment differs fundamentally. Adenomas may require surgical resection, whereas GPA-associated hypophysitis is treated with immunosuppression.

Conclusion:

GPA-associated hypophysitis should be considered in patients with pituitary masses and systemic inflammatory features. Early recognition and tissue diagnosis are essential to guide appropriate immunosuppressive therapy and avoid unnecessary surgical intervention.

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