Unilateral itchy plaques

A 14-year-old Japanese girl visited our outpatient clinic with therapy-resistant, unilateral, itchy plaques. She had been treated in a private clinic for what was considered psoriasis and was administered topical steroid and calcipotriol hydrate with inadequate effects. At her initial visit, physical examination revealed brown to skin-coloured, infiltrated, scaly erythema and papules on her left trunk, upper limbs, and lower extremities along the Blashko line (Figure 1 a, b, c, d). A full blood count and biochemical profile were within normal ranges. A biopsy specimen showed elongated rete ridges, parakeratosis, and dilated tortuous vessels in the dermal papillae (Figure 1d) and neutrophils were rarely detected in the specimen.