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Eruptive melanocytic naevi secondary to azathioprine: case report and review of the literature

A 33-year-old woman presented with a 2-month history of multiple, recent onset pigmented small lesions on her soles. She had a background of ulcerative colitis (diagnosed 6 years previously), and had been on azathioprine 100 mg daily for the past year. Previously she had been given treatment with oral steroids, but had received no other immunosuppressive agents. Physical examination revealed multiple (five on the right and two on the left sole) macular, mid-brown lesions, which were clinically and dermoscopically consistent with junctional melanocytic naevi (MN) (Fig. 1). A full examination was otherwise unremarkable. The patient was diagnosed with common acquired melanocytic MN, reassured of their benign nature and discharged with no further planned follow-up. Common acquired MN tend to appear mainly on sunexposed sites during the first 4 decades of life, and reach a peak at approximately 30 years of age. They are then believed to slowly involute and decrease in number with increasing age. Known risk factors for large numbers of MN include young age, male sex, sun exposure, and light-coloured skin, eyes and hair. In contrast to common MN, eruptive MN are rare and characterized by simultaneous, rapid development of multiple MN, often in a grouped distribution, on skin that previously appeared normal. The palms of the hands and the soles of the feet are the usual sites of predilection for MN, for reasons that are poorly understood. Eruptive MN have been documented following bullous dermatoses such as Stevens–Johnson syndrome and epidermolysis bullosa, and in immunocompromised patients, such as those with human immunodeficiency virus infection, or those on treatment with cancer chemotherapy, biologics or BRAF inhibitors, and finally, as in our patient, azathioprine. Occasionally, eruptive MN may arise without any obvious apparent precipitating factors. The pathophysiology of eruptive benign MN remains unknown. It is possible that an intact immunological state normally inhibits the proliferation of melanocytic lesions. Changes in the immune system can potentially induce endogenous growth factors to allow proliferation of melanocytes. The palms and soles are likely to Correspondence: Dr Georgios Kravvas, Department of Dermatology, NHS Lothian, Lauriston Building, Lauriston Place, Edinburgh, EH3 9EN, UK E-mail: kravvas@hotmail.com