An erythematous plaque in the left thumb of a 58-year-old woman

Abstract

A 58-year-old woman presented with an ill-defined erythematous plaque on volar aspect of the promixal interphalangeal joint of her left thumb for 3 months. The plaque (1.0 cm × 0.7 cm) was mildly elastic and tender on palpation (Figure 1). There was no scaling, vesiculation or ulceration. She denied previous trauma in this area. Upon physical examination, no regional lymphadenopathy or systemic finding was noted. An incisional biopsy of the plaque was performed. Pathological sections showed an infiltrative, vaguely multilobular tumor in the dermis and subcutaneous fat (Figures 2A and 2B). It was composed of mildly pleomorphic cells in intermixing fibrous and myxoid stroma. Most tumor cells were spindled in shape. Some epithelioid ganglion-like cells with large nuclei and prominent eosinophilic nucleoli were also noted. Occasional binucleated giant cells resembling Reed-Sternberg cells were present (Figure 3A). Mitotic figures were rare. Dense inflammatory infiltrates including lympho cytes, histiocytes and a few eosinophils were noted in the background. The overlying epidermis showed hyperkeratosis and was otherwise unremarkable. Immunohistochemical staining results showed that the majority of tumor cells were positive for CD68 (Figure 3B) and CD34 (Figure 3C).