Generalized linear porokeratosis

A 23‐year‐old woman was seen for widespread skin lesions present since the age of 2.5 years. Twenty years ago, she developed a brown macular lesion on her right buttock. The lesion became hyperkeratotic and subsequently spread through the posterior aspect of her right leg. It later spread to the right side of the trunk and to the right arm. When she was 9 years old, she developed similar lesions on her left arm and leg. After she was 13 years old, no new skin lesions appeared. There was no family history of similar lesions. On examination, there were numerous linear and whorled, reddish‐brown, hyperkeratotic plaques, with central atrophy and raised borders, following Blaschko's lines on all of the extremities. These lesions on the extremities extended to the dorsum of the hands and feet ( Fig. 1). She had hyperkeratotic lesions on the pressure points of both of the soles, but no palm involvement. The number of lesions on the right side was greater than that on the left. Reddish‐brown annular plaques with central atrophy and raised borders, appearing in zosteriform configuration, and numerous individual 2–3‐mm erythematous lichenoid papules were observed on the right side of the thorax and the right inguinal region ( Fig. 2). No face, scalp, or mucous membrane involvement was seen. The nails of the second and fifth fingers of the right hand and the nail of the third finger of the left hand showed nail dystrophy with longitudinal ridges and pterygium. All the nails of the right foot and the nails of the first and fifth toes of the left foot showed dystrophic changes with subungual keratosis. The patient was otherwise in good health. 1Linear erythematous plaques with central atrophy and raised borders on the lower extremities2Annular plaques and lichenoid papules with zosteriform configuration on the right thoracoabdominal region Two biopsy specimens taken from a hyperkeratotic plaque and a lichenoid papule showed an epidermal invagination with angulated parakeratotic tier, denoting cornoid lamella. The epidermis just underneath the cornoid lamella displayed vacuolization and the granular layer was absent. The adjacent epidermis was atrophic, and hydropic degeneration within the basal cell layer was seen. In the dermis, a nonspecific, mild, chronic, inflammatory cell infiltrate, telangiectatic vessels, and pigment‐laden macrophages were present. These findings were consistent with linear porokeratosis ( Fig. 3). Microscopic examinations and mycologic cultures of the nails were negative. 3Linear porokeratosis: cornoid lamella, vacuolization, and absence of granular layer underneath (hematoxylin and eosin, ×400) We decided to treat our case systemically with retinoids, but the patient refused this therapy. So, topical tretinoin 0.05% was started once a day. A marked improvement was observed in hyperkeratosis through the first 4 weeks of treatment and plateaued at 8 weeks. After 10 weeks, the lesions had almost disappeared. We planned to continue the applications every other day. One year later, she remains stable with application of topical tretinoin 0.05% twice a week and is satisfied with the final appearance. She is under regular follow‐up.