Azathioprine hypersensitivity: A Sweet‐like syndrome

Introduction Azathioprine hypersensitivity can occasionally present as Sweet‐like syndrome, a dose‐independent side effect characterized by the unanticipated onset of macules, papules, and pustules. Case presentation A 35‐year‐old woman with systemic lupus erythematosus presented with complaints of generalized maculopapular rash, facial swelling, and bilateral lower extremity edema with a duration of 4 days and a 2‐day history of constitutional symptoms within 2 weeks of the beginning of azathioprine therapy to treat existing lupus nephritis (class 2/3). Discussion Patients who experience azathioprine hypersensitivity syndrome can present with erythema nodosum, small‐vessel vasculitis, acute generalized exanthematous pustulosis, Sweet syndrome, and nonspecific dermatosis. The following signs and symptoms are used as criteria to diagnose drug‐induced Sweet syndrome: (a) abrupt onset of painful erythematous plaques, (b) histopathological evidence of dense neutrophilic infiltrate without evidence of leukocytoclastic vasculitis, (c) temperature higher than 39.7°C, (d) temporal relationship between drug ingestion and clinical presentation, and (e) temporal resolution of lesions after drug withdrawal. Our patient met three out of five criteria and was diagnosed with Sweet‐like syndrome. Conclusion Our case highlights the uncommonly presented azathioprine‐induced Sweet‐like syndrome that occurs abruptly after the commencement of the offending drug. This diagnosis can be established through basic laboratory workup and skin biopsy findings.