Chromoblastomycosis Can Mimic Keratoacanthoma

A 59‐year‐old white man presented to the Dermatology Clinic at the University of Texas Medical Branch with ti verrucous nodule on the right forearm. The patient was a retired woodworker. He had polytiiyositis with pulmonary fibrosis for 5 years. Prednisone and mcthotrexate were required to control his disease. A crusted verrucous nodule 2.5 by 2.5 cm in diameter with adjacent similar‐sized atrophic scars were present on the extensor surface of the right forearm (Fig. 1). This particular nodule had been present for 2 years, and its growth was characterized by a rapid onset with progressive enlargement and intermittent partial regression. The adjacent scars represented similar lesions that had spontaneously regressed. Although the patient had not worked since his illness began, he continued to actively pursue woodworking as a hobby. Histologic sections of the excised nodule revealed massive pseudoepitheliomatous hyperplasia with prominent hyper‐keratosis. Intraepidermal microabscesses were numerous and a suppurative neutropbilic infiltrate with scattered foreign body type multinucleated giant cells was present in the dermis (Fig. 2). At higher magnification, numerous light brown yeasts, approximately 10 μm in diameter (Fig. 3) were noted both within tbe giant cells and free within the dermis. Chains of yeast cells were common. These histologic findings are diagnostic of chromoblastomycosis.³