Azathioprine hypersensitivity presenting as a neutrophilic dermatosis in a man with ulcerative colitis

We report a case of a 46-year-old man with ulcerative colitis being treated with oral prednisolone and azathioprine. Two weeks after the initiation of azathioprine he presented with fever, fatigue, myalgias and arthralgias and a painful cutaneous eruption that was most marked in a sun-exposed distribution. This was accompanied by loose, non-bloody diarrhoea. Histopathological assessment of a skin biopsy supported a diagnosis of a neutrophilic dermatosis. The azathioprine was temporarily withheld and oral prednisolone was increased as it was thought that the neutrophilic dermatosis was associated with the underlying ulcerative colitis. The patient's symptoms and cutaneous eruption resolved quickly and azathioprine was re-introduced. Within 24 h, systemic symptoms returned along with a florid recrudescence of his cutaneous eruption. This rapidly improved upon withdrawal of azathioprine.