[Intermittent fever of unknown origin]

A 58-year-old woman was admitted because of intermittent fever for 4 weeks accompanied by slowly developing anaemia and increase in inflammatory parameters. She was being treated for hypertension with atenolol and chlorthalidone, but until 6 weeks before the onset of the described symptoms she had only taken the beta blocker, at which time the diuretic was added because the hypertension was inadequately controlled. Other than slightly impaired general condition and nocturnal fever up to 39.5 degrees C physical examination was unremarkable.

She had a normochromic normocytic anaemia and the erythrocyte sedimentation rate and C-reactive protein were clearly elevated. Other biochemical tests and blood cultures as well as serological and immunological tests were negative. Bone marrow biopsy showed nonspecific reactive changes. The chest radiograph, lung scintigraphy and abdominal ultrasound were unremarkable.

There was no further fever after the antihypertensive medication had been discontinued. The patient's general condition rapidly improved and all biochemical tests became normal. The lymphocyte transformation test demonstrated stimulation by chlorthalidone.

Drug fever, in this case due to a sulphonamide derivative, should always be considered in the differential diagnosis of fever of unknown aetiology. No previous case of hypersensitivity reaction to chlorthalidone has been found on a search of the literature.