[Diabetes insipidus in a patient with small-cell lung cancer: a paradox?].

We observed oat-cell lung carcinoma in a man who presented with diabetes insipidus. The chest radiograph showed a suspect nodule within a context of major nicotine addiction. Histopathological examination of the transbronchial biopsy confirmed the diagnosis of oat-cell carcinoma. Brain CT revealed metastasis to the pituitary gland and the pituitary stalk. Vasopressin was undetectable. This case illustrates an uncommon clinical presentation of small-cell lung carcinoma. Oat-cell carcinoma can modify osmoregulation in two different ways. Only sporadic cases of neurogenic diabetes insipidus due to the primary involvement of small-cell lung carcinoma have been reported. More often, this type of lung tumor is associated with inappropriate antidiuretic hormone secretion.