Pilomatrixoma

Photoclinic
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A 14-year-old girl was concerned about this 1-cm, red, nodulocystic lesion on her left posterior shoulder that had been present for several months. The lesion had developed over the site at which a 0.5-cm pilomatrixoma had been excised a year before. Four years earlier, another 1.9-cm pilomatrixoma had been excised from the girl’s right outer upper arm. There was no family history of the lesion.

The lesion was excised under local anesthesia in the office without complications. The diagnosis was pilomatrixoma (Malherbe calcifying
epithelioma).

Pilomatrixomas are derived from hair matrix cells and are almost always benign; only 1 malignancy was reported in a study of 209 cases.¹ These usually solitary tumors occur most commonly on the face, neck, and arms. They range from 0.5 to 7 cm, often penetrate deep beneath the skin, and have a pink or skin-colored nodular top. Their occurrence peaks at age 5 to 10 years and at age 50 to 65 years; however, they have developed in patients as young as 18 months and as old as 86 years.¹ The lesions may be seen with myotonic dystrophy (myotonia atrophica). They may also be familial. Multiple pilomatrixomas have been associated with Rubinstein-Taybi and Gardner syndromes. Histologically, the lesions are encapsulated masses with basophils and shadow cells. Calcification, melanin deposits, and foreign-body reaction with giant cells may be present.

The best treatment is simple excision, although curettage through a keyhole opening has been successful. ■