Localized pigmentation disorder after subcutaneous pegylated interferon beta-1a injection

We report the case of a 42-year-old female patient who developed peculiar skin lesions due to subcutaneous polyethylene glycol (PEG) interferon beta-1a. The dermatological examination showed hypochromic macules that had coalesced into a 10-cm-diameter patch. On the abdomen injection sites, there was a greyish diffuse hyperpigmentation arranged irregularly in annular macules. Fungal infection, vitiligo and pityriasis alba were excluded. After 6 months, the lesions had worsened. This is the first case of localized pigmentation disorder reported with interferon beta, and while the clinical findings are not ascribable to vitiligo or interferon-related facial/mucosal hyperpigmentation, they may partially share the underlining mechanisms.