Primary Central Nervous System Lymphoma with Central Diabetes Insipidus and Hypopituitarism: Diagnostic Pitfalls in the “Ghost Tumor” with Steroid-induced Lymphocytolysis

Primary hypothalamic involvement in primary central nervous system lymphoma is rare and can present with nonspecific neurological and endocrine manifestations, resulting in significant diagnostic delays. We report the case of an immunocompetent 29-year-old female who presented with intermittent fever, seizures, progressive behavioral changes, central diabetes insipidus, and hypopituitarism. She was initially treated empirically for encephalitis with anti-epileptics and corticosteroids. Neuroimaging subsequently demonstrated a homogeneously enhancing lesion along the chiasmatic-hypothalamic axis. Initial biopsy was nondiagnostic due to corticosteroid pretreatment, necessitating repeat biopsy via craniotomy, which confirmed diffuse large B-cell lymphoma. This case illustrates the importance of recognizing endocrine red flags in hypothalamic lesions, emphasizes the negative impact of prebiopsy steroid exposure on diagnostic yield, obscuring histopathology even in the absence of radiological regression.