SUN-054 - Pituitary Metastasis Causing Hypopituitarism in HIV-Associated Diffuse Large B-Cell Lymphoma

Background:
Hypopituitarism due to pituitary metastases is rare, particularly from hematologic malignancies, with lymphoma accounting for fewer than 0.5% of reported pituitary metastases. We describe a patient with newly diagnosed HIV who presented with panhypopituitarism due to pituitary infiltration by diffuse large B-cell lymphoma (DLBCL).
Clinical

Case:
A 56-year-old man with no prior medical history presented with fatigue, back pain, and progressive lower-extremity weakness. Imaging revealed a T10 epidural mass with spinal cord compression, and surgical resection confirmed CD20-positive DLBCL. Further evaluation revealed newly diagnosed HIV infection with a CD4 count of 113 cells/mm³. Endocrine evaluation demonstrated hypopituitarism, including central hypothyroidism (TSH 0.226 µIU/mL, FT4 0.3 ng/dL) and hypogonadotropic hypogonadism (total testosterone < 10 ng/dL with low gonadotropins). Adrenal axis testing was deferred due to ongoing systemic glucocorticoid therapy administered as part of lymphoma management. MRI of the sella demonstrated abnormal pituitary enhancement with loss of the normal posterior pituitary T1 hyperintensity, consistent with pituitary infiltration by lymphoma. The patient was treated with systemic chemotherapy and intrathecal therapy for CNS involvement, as well as antiretroviral therapy. At discharge, he was prescribed hydrocortisone 10 mg each morning and 5 mg each evening for presumed adrenal insufficiency and levothyroxine 75 µg daily for central hypothyroidism.

Discussion:
Despite prominent neurologic symptoms from spinal cord compression, endocrine evaluation for fatigue led to the diagnosis of hypopituitarism, emphasizing the importance of comprehensive assessment in patients with malignancy. Central hypothyroidism is the most frequently reported endocrine abnormality among the approximately 34 reported cases of pituitary involvement by lymphoma. Diagnosis is often based on clinical and radiographic findings, with biopsy rarely required due to favorable responses to systemic therapy and the limited role of pituitary surgery.

Conclusion:
In patients with HIV presenting with rapid-onset panhypopituitarism and atypical sellar imaging, metastatic pituitary involvement by DLBCL should be considered, particularly in the setting of concurrent CNS disease.

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