br Introduction Lichen planus pigmentosus inversus

Introduction Lichen planus pigmentosus-inversus (LPPI) is a rare variant of lichen planus characterized by mottled pigmentation of bluish, black, or grey color on the flexural folds. We describe a similar case of a patient whose lesions were distributed along Langer\'s lines of skin cleavage over the submammary and inguinal skin folds.
Case report A 49-year-old Chinese female presented with a 5-month history of insidiously developing pigmented macules along skin cleavage lines over the submammary and inguinal skin folds. This slate-grey macule began on the submammary skin folds and then spread to the inguinal area without noticeable inflammatory changes. No drugs were taken prior to development of the eruption. She denied any infection of hepatitis B or C virus. There was no history of fever, weight loss, or exacerbation of the eruption upon sun exposure. On examination, multiple, discrete and slate-grey macules distributed along the skin cleavage lines over submammary and inguinal folds were observed. The chest, epigastric area, and upper thighs were less frequently affected. The macules were approximately 2 mm in diameter, and did not coalesce, forming several, intermittent and brownish lines. These lines obviously were unrelated to Blaschko\'s lines and dermatome lines (Figure 1). The mucous and the nail were not affected. General systemic examination revealed no abnormalities. Routine laboratory tests including peripheral blood lrrk2 and liver function were all within normal limits. A biopsy specimen from the left inguinal skin lesion showed atrophic epidermis with foci of colloid bodies. In the superficial dermis, there was a dense lymphohistiocytic infiltration with prominent melanophages (Figure 2), which were in accordance with the pathological alterations in regressive lichen planus. Based on all these clinical and histological findings, the patient was diagnosed with LPPI following skin cleavage lines.
Discussion LPPI is an uncommon type of lichen planus reported first by Pock et al in 2001. Subsequently, it was observed to occur in other racial and ethnic groups, and >27 cases have been reported in English literature do date. LPPI is most often seen in the 3rd decade to 5th decade of life. There is a slight female preponderance. The lesions seen in LPPI are mostly asymptomatic and occur most often over the axillae and groin. Other skin parts, such as the neck, abdomen, popliteal regions, inframammary folds, antecubital fossae, waist, inner wrist, and auricular sulci are also likely to be involved. LPPI was reported to start insidiously as a small, ill-defined and oval to round macule, which coalesced to a confluent sheet of pigmentation. Its color varied from slate-blue to steel grey or brown. Occasionally, the macules were distributed in a linear, blaschkoid, reticular, blotchy, or perifollicular morphology. However, intermittent lines over the skin cleavage, as shown in our case, had not been reported previously. Histologic features that characterize LPPI vary according to its stage. A band-like infiltration of lymphocytes characterizes its earlier stage, with moderate melanophages scattered in the dermis. Additionally, there is notable vacuolar degeneration of the basal layer and colloid bodies in the epidermis. Meanwhile, the old lesion is accentuated with superficial, mild, lymphohistiocytic infiltration with frequent interstitial and perivascular melanophages. In the epidermis, it usually shows focal or absent vacuolar degeneration, few apoptotic keratinocytes, and atrophy of the epidermis with compact hyperkeratosis. The pathological findings in our case were overall in accordance with those in late-stage LPPI. It is well known that dermatome lines, Blaschko\'s lines, and Langer\'s lines (or skin cleavage lines) are three major line forms described that cover the human body. Langer\'s lines were revealed in 1861 by Karl Langer (1819–1887). Langer\'s lines run along the natural orientation of collagen fibers and underlying muscle fibers, thus, they have a significant relevance especially to surgical techniques. In dermatology, several skin disorders have been reported to be distributed along these lines. Essentially, they are pityriasis rosea and mycosis fungoides, as well as stage two syphilis, exanthematic sarcoma idiopathicum multiplex, hemorrhagicum Kaposi, creeping hair, the early stages of psoriasis vulgaris, Wolf\'s isotopic response, Leser-Trelat syndrome, Saurian papulosis, idiopathic eruptive macular pigmentation, and dermatosis papulosa nigra. LPPI can be differentiated from these by its typical clinical and his histological characteristics.