Metastatic large cell neuroendocrine carcinoma: a rare cause of hypopituitarism.

Pituitary metastases from pulmonary large cell neuroendocrine carcinoma (LCNEC) are exceedingly rare but should be considered in patients presenting with arginine vasopressin deficiency and panhypopituitarism in the context of known or suspected metastatic lung cancer. Early recognition and prompt initiation of hormonal replacement therapy are essential to prevent life-threatening endocrine crises and to improve symptom burden. We describe a case of a 43-year-old male who presented with dyspnea, weight loss, and weakness who was found to have metastatic LCNEC involving the liver. Endocrine evaluation revealed central hypothyroidism, central adrenal insufficiency, and later arginine vasopressin deficiency manifested by polyuria and hypernatremia. Additional pituitary testing demonstrated central hypogonadism and growth hormone deficiency consistent with panhypopituitarism. Magnetic resonance imaging showed a sellar mass with pituitary stalk thickening consistent with metastatic disease. Alternative infectious and infiltrative etiologies were excluded. Although the prognosis remains poor due to the aggressive nature of LCNEC, this case underscores the importance of a multidisciplinary approach with endocrinology, oncology, and palliative care to optimize management and quality of life in patients with advanced disease.