Bacterial overgrowth after high-dose corticosteroid treatment.

A 63-year-old man with systemic lupus erythematosus and selective IgA deficiency developed intractable diarrhoea the day after treatment with prednisone, 50 mg daily, was started. The diarrhoea was considered to be caused by bacterial overgrowth and was later successfully treated with doxycycline. Although IgA deficiency is a risk factor for bacterial overgrowth, a further predisposing condition is necessary for development of this disorder but was not present in this case. We therefore suppose that high-dose treatment with corticosteroids might be a hitherto undescribed risk factor for bacterial overgrowth in vulnerable patients.