[Perforating lichen nitidus on an atypical site].

To the Editor: Lichen nitidus is a rare disorder characterized by multiple, skin-colored, micropapular lesions with a smooth, shiny surface, located preferentially on the flexor surface of the arms and wrists and on the abdomen and genitalia, though they can become generalized. Histological study shows a lymphohistiocytic infiltrate that broadens the dermal papillae and that is limited laterally by elongated rete ridges. The variants described include vesicular, hemorrhagic, linear, keratodermic, generalized, actinic, and perforating forms. There are only 5 case reports of perforating lichen nitidus.1-4 We report a case of perforating lichen nitidus that affected the lateral borders of the fingers. The patient was a 35-year-old man who was seen for evaluation of asymptomatic lesions on the fingers and toes; the lesions had been present more than 20 years. The patient had received treatment with topical corticosteroids with virtually no response. On examination, skin-colored, shiny, firm, monomorphic papules of 1 mm in diameter were observed on the palms, the dorsum of the feet, and lateral borders of the fingers (Figure 1). Two biopsies were taken from these lesions, with similar findings in both samples. There was a lymphohistiocytic infiltrate in a broadened dermal papilla, with descending growth of the rete ridges surrounding the dermal inflammatory infiltrate like a hook (Figure 2). The patient had been seen for the same disorder 9 years earlier in another center; biopsy had been performed and, apart from the findings described above, the histology showed transepidermal elimination of collagen and keratin (Figure 3). The condition was therefore lichen nitidus that, during its course, had developed perforating lesions. In view of the resistance to previous treatment with topical corticosteroids, topical tacrolimus was prescribed, with a minimal response of the lesions. Lichen nitidus is a rare condition and the appearance of perforating lesions is exceptional. We have only found 5 cases of perforating lichen nitidus reported in the literature (Table), all in young patients. In addition, our patient presented involvement of the lateral borders of the fingers, an unusual site.5 The primary perforating dermatoses include elastosis perforans serpiginosa, reactive perforating collagenosis, and acquired perforating dermatosis. The secondary forms, in which the transepidermal elimination is a consequence of another, underlying disorder, include perforating variants of calcinosis cutis, annular granuloma, chondrodermatitis nodularis helicis, lichen planus, and lichen striatus.4 Elastosis perforans serpiginosa and reactive perforating collagenosis are diseases of unknown origin, although there may be a hereditary factor. Elastosis perforans serpiginosa may be associated with Down syndrome and connective tissue diseases; it is characterized by keratotic papules of 2 to 5 mm that tend to be organized in a serpiginous or