Hyponatraemia masking the diagnosis of cryptococcal meningitis.

Patients with acute hyponatraemia present with neurologic symptoms resulting from cerebral oedema induced by water movement into the brain. The author reports a male patient who presented to our emergency department with headache for 3 days and confusion for a day. The reported patient was on two immunosuppressive drugs, namely prednisone and azathiorprine for his ulcerative colitis. Laboratory data were consistent with syndrome of inappropriate antidiuretic hormone secretion (SIADH) which was appropriately corrected; however his mental status deteriorated. The patient's initial presentation was considered to be secondary to hyponatraemia. There was lapse of 36 h where the hyponatraemia was corrected; however the cause of the SIADH was not investigated. On further investigation of the patient a diagnosis of cryptococcal meningitis was ascertained. This case highlights the importance of considering a central nervous system infection in an immuno-suppressed patients presenting with hyponatraemia secondary to SIADH.