SAT-056 - Rapidly Progressive Infundibular Hypothalamic Lymphocytic Hypophysitis Mimicking Primary CNS Lymphoma

Lymphocytic infundibulo-hypothalamic hypophysitis is a rare autoimmune inflammatory disorder that may extend beyond the pituitary stalk to involve the hypothalamus. When rapidly progressive, it can closely mimic primary CNS lymphoma (PCNSL) both radiographically and clinically, creating major diagnostic and management challenges, especially when biopsy is prohibitively risky .

A 66-year-old woman presented with 2 years of polyuria that progressed to cognitive decline, lethargy, and visual disturbances. MRI showed pituitary stalk thickening suggestive of Infundibulo-neuro-hypophysitis. She developed arginine vasopressin deficiency (AVPD with sodium 149, serum osmolality 314 mOsm/kg; urine osmolality 113 mOsm/kg), requiring desmopressin. Over 18 months, serial MRIs revealed rapid evolution of hypothalamic mass extending into the optic chiasm and ventral medial thalami with evolving T2/FLAIR hyperintensity in the anterior commissure and posterior limb of the internal capsule. MR spectroscopy findings were suspicious for lymphoma, a known diagnostic pitfall in inflammatory hypothalamic lesions and primary CNS lymphoma .
Further evaluation clarified the diagnosis. Extensive assessment included cerebrospinal fluid analysis (≤6 WBC, glucose, mildly elevated protein, negative cytology, flow cytometry, JC virus, MTB PCR, HSV, VDRL), bronchioloalveolar lavage and lung nodule biopsy. No evidence for malignancy or infection was noted. AFP, hcg, ACE and IgG4 levels were normal. CT-guided biopsy of a concurrent lytic iliac/sacral lesion showed polyclonal CD20+/CD3+ lymphoid infiltrates with low IgG4 burden (20%), arguing against lymphoma or IgG4-related disease. Neurosurgical biopsy was repeatedly deferred due to high procedural risk.
During this period, the patient developed anterior hypopituitarism as well, manifesting as central hypothyroidism (TSH 0.68, free T4 0.62 ng/dl), hypogonadotropic hypogonadism (FSH 0.9 IU/L), hyperprolactinemia (peak 103 ng/ml), along with persistent AVP deficiency. High-dose intravenous corticosteroids were initiated, leading to clinical stabilization. Early imaging showed minimal change. However, prolonged steroid therapy produced marked radiographic regression, with near-complete resolution of hypothalamic enhancement and FLAIR abnormalities by 10 months.

This case highlights a rare, rapidly progressive lymphocytic infundibulo-hypothalamic hypophysitis with delayed, sustained steroid responsiveness. The condition closely mimics PCNSL. Early recognition of stalk-centered disease, thorough evaluation for malignancy, and longitudinal imaging follow-up are critical. These steps can help guide management in cases where definitive diagnosis via a biopsy is considered too high risk and may not be possible.

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