[Clinical thinking and decision making in daily practice. An elderly man with hyponatremia].

An 88-year-old man presented with nausea and vomiting. Recently a cutaneous B-cell lymphoma had been diagnosed on his right cheek. Laboratory investigation showed hyponatraemia. Fluid restriction was started, based on the diagnosis of the syndrome of inappropriate antidiuretic hormone secretion (SIADH). However the hyponatraemia persisted and a diagnosis of 'reset osmostat' was made. CT of the abdomen revealed slight bilateral adrenal enlargement, which was interpreted as adrenal incidentaloma. No other localisation of the lymphoma, besides that on the right cheek, was seen. Although the symptoms initially disappeared, they recurred and were quickly followed by hypotension. The patient died. Post-mortem examination showed bilateral destruction of the adrenal glands due to lymphoma. The correct diagnosis was Addison's disease. This case shows that diseases do not always present with all the classical symptoms, and that it is important to consider test characteristics of diagnostic tests and to judge investigations in the context of the other clinical findings.