Azathioprine hypersensitivity: A Sweet-like syndrome

Azathioprine hypersensitivity can occasionally present as Sweet-like syndrome, a dose-independent side effect characterized by the unanticipated onset of macules, papules, and pustules.

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).

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.

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.