Lichen planus pigmentosus-inversus.

We examined seven patients with lichen planus pigmentosus (LPP) clinically and microscopically. Clinically, all patients had a striking predominance of lesions in an intertriginous location, with most of them in the axillae. Microscopically, two biopsies were of significance. Except for the regressive lichen planus, which is usual in LPP, the active inflammatory phase was also present. In these biopsies the very intensive hydropic degeneration of basal keratinocytes was combined with the absence of compensatory increased proliferation of keratinocytes, i.e. without acanthosis. The short duration of this process probably led to the quick transformation into a long noninflammatory regressive phase with incontinence of the pigment. These specific morphogenetic dynamics are possibly why most of the morphs of LPP present as brown, non-pruritic, small inflammatory macules. Because of the highly characteristic inverse location of the lesions in our patients we propose the designation LPP-inversus for this variant of the disease.