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June 1989

Solitary Hard Nodule on the Forearm

Author Affiliations

Cook County Hospital, Chicago, Ill

Arch Dermatol. 1989;125(6):831-832. doi:10.1001/archderm.1989.01670180103019

REPORT OF A CASE  A 57-year-old man presented with a 2-year history of a slowly enlarging, asymptomatic nodule on the right forearm. There was no history of trauma to the area, and the patient's medical history was otherwise insignificant.Physical examination disclosed a 2.0 × 2.5-cm, erythematous, hard, freely mobile, elevated nodule on the anterior aspect of the proximal right forearm (Fig 1). No lymphadenopathy was present. The remainder of the physical examination was normal.Representative sections of an excisional biopsy specimen are shown (Figs 2 and 3).What is your diagnosis?

DIAGNOSIS  Pilomatricoma

HISTOPATHOLOGIC FINDINGS  Microscopic sections of hematoxylin-eosin-stained tissue revealed a nodule composed predominantly of masses of large eosinophilic-staining cells that were devoid of nuclei but had well-defined cell outlines (shadow cells). Small collections of densely packed cells with deeply basophilic-staining oval nuclei and poorly demarcated cell boundaries were found at the periphery of the tumor. Transitional zones were present in which the basophilic cells merged abruptly with areas of shadow cells (Fig 3). Microscopic sections of tissue showed foci of calcification within

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