Porokeratotic lichen planus

A 16-year-old male presented with multiple lesions involving the lips, shoulder region, extremities and glans penis for the last 1 year. The individual lesions began as small papules that gradually increased to form small, annular, barely palpable plaques. There was no history of oral symptoms or immunosuppression. Cutaneous examination revealed multiple hyperpigmented, annular papules and plaques ranging from 0.5 to 4.0 cm in size with a thready margin over the lips, shoulder region, upper and lower extremities, soles of the feet (Figure 1a, b) and the glans penis. There was no central atrophy. Oromucosal examination revealed an irregular, brownish plaque on the right mucosa with a thready, white, elevated margin. Clinical differential diagnoses of porokeratosis (Mibelli) and annular lichen planus were considered. Dermatoscopy of the lesion on the foot demonstrated a white hyperkeratotic border with dotted vessels and a central area of patchy brownish pigmentation characteristic of porokeratosis (Figure 1c). Biopsies were taken from a lesion on the lower extremity and from oral mucosa for pathologic examination. The cutaneous biopsy showed a hyperkeratotic epidermis with mild lymphocytic exocytosis and spongiosis. A band-like lymphocytic infiltrate was noted in the interphase region and in the papillary dermis along with pigmentary incontinence (Figure 2a, b). The mucosal biopsy showed a dense chronic inflammatory infiltrate along with pigmentary incontinence in the subepithelial zone. Basal cell vacuolation was also noted (Figure 2c). A cornoid lamina was not seen in any of the pathologic sections examined, including further deeper sections and a repeat biopsy. The clinical morphology, dermatoscopic features, and pathology were therefore considered compatible with a diagnosis of porokeratotic lichen planus. Lichen planus is a common papulosquamous inflammatory dermatosis of unknown etiology that presents in a number of morphologic patterns and clinical variants [1–3] and can involve the skin, mucosa and hair as well as the nails [4]. Porokeratosis is a clonal disorder of keratinization that manifests clinically as centrifugally expanding, annular plaque(s) with a ridge-like margin – the cornoid lamella. Cornoid lamella is the diagnostic hallmark, and histology shows a column of tightly packed parakeratotic cells within DOI: 10.1111/ddg.13953 Porokeratotic lichen planus Clinical Letter