[Hyponatremic coma as the first symptom of a small cell bronchial carcinoma]

A 50-year-old man was admitted to hospital because of vertigo for 3 weeks. He was found to have severe hyponatraemia (107 mmol/l), which was rectified with sodium chloride infusions. Two weeks later he became agitated with confusion and hallucinations. Within a few hours he went into coma. At that time the serum sodium concentration had again fallen from 132 to 105 mmol/l. Repeated measurement revealed urinary osmolality (558 mosm/l) to be above that of serum (252 mosm/l), pointing to the syndrome of inadequate antidiuretic hormone secretion (SIADH) as the diagnosis. Lung tomography, performed because the patient had two bouts of pneumonia in quick succession, demonstrated enlarged hilar lymph nodes. Bronchoscopy revealed a tumour of about 1.0 cm diameter in the left main bronchus which histologically proved to be a small-cell bronchial carcinoma. Despite chemotherapy the tumour progressed and the SIADH also persisted. The patient died 9 months later of heart failure.