Unusual halo nevi--darkening rather than lightening of the central nevus.

Although the classic halo nevus is a brown nevus with a surrounding rim of depigmentation, i.e. a stage I halo nevus, these nevi can have several clinical stages. The central nevus may lose its pigmentation and appear pink with a surrounding halo (stage II), the central papule may disappear leading to a circular area of depigmentation (stage III) or the depigmented area may repigment (stage IV), leaving no trace of its prior existence. Herein we describe an unusual phenomenon--darkening of the central nevus rather than lightening--following the appearance of the halo phenomenon. An 18-year-old boy who had multiple atypical nevi developed multiple halo nevi beginning at the age of 12 years. Following the appearance of the peripheral halos, 2 of his nevi that were originally solid medium brown in color darkened and the hyperpigmentation had a reticulated pattern with perifollicular sparing. One possible explanation is a postinflammatory hyperpigmentation induced by the infiltrating lymphocytes.