An itching plaque

A 30-year-old woman presented to our hospital in Manacor, Mallorca, with a new lesion on the thorax that had appeared three to four months earlier, had gradually enlarged and was slightly itchy. The patient was otherwise healthy. Physical examination revealed a tender, brownish papule or plaque contacting the elastic band of the underwear under the right breast (Figure 1). The remaining physical exam showed no other relevant lesions. Dermoscopic examination showed an ill-defined redyellowish background with a small, pigmented, structureless area. Tiny, dotted and comma vessels were barely visible. Remarkable were numerous rounded or droplet-shaped, whitish structures spread all over the lesion (Figure 2). A 3 mm punch biopsy was obtained showing epidermal acanthosis and an intense superficial dermal inflammatory infiltrate. The infiltrate was composed by neutrophils, eosinophils and plasma cells, intermingled with bigger epithelioid cells, some of them containing tiny, round, basophilic structures in their cytoplasm (Figure 3). What is your diagnosis?