Azathioprine hypersensitivity syndrome: report of two cases

Azathioprine hypersensitivity syndrome is a rare but potentially severe side effect of azathioprine use. It has a variable and non-specific presentation making it difficult to distinguish from sepsis or disease relapse. High clinical suspicion is therefore required for recognition and prompt cessation of azathioprine for symptom resolution. Herewith two cases of severe azathioprine hypersensitivity syndrome are described, one in association with Sweet syndrome. Both presented with vague symptoms 2 weeks after commencing azathioprine for antineutrophil cytoplasmic antibody vasculitis. The differentials of sepsis and disease relapse were considered prior to cessation of azathioprine which resulted in a dramatic improvement in both cases. These cases highlight the diagnostic challenge azathioprine hypersensitivity syndrome presents. It should be suspected when there is a temporal relationship to drug initiation, with absence of infection or serological evidence of disease relapse.