A 58-year-old male presents for evaluation and treatment of a lesion on his arm that was first noted approximately 4 months ago and that has continued to enlarge in size. He denies antecedent trauma, localized infection, history of similar lesions, and systemic disease. The site is asymptomatic. Physical examination reveals a slightly elevated hyperkeratotic central plaque of 0.6 cm overlying a 1.5-cm dermal nodule. Palpation does not elicit tenderness.
Submit your diagnosis to see full explanation.
The lesion was excised and histopathology revealed a pilomatricoma, an uncommon tumor formerly named calcifying epithelioma of Malherbe. Although originally thought to be far more prevalent in children, a large review revealed a bimodal distribution with two peaks: Children aged 5 to 15 years and adults aged 50 to 65 years.1
The majority of lesions occur on the head and neck2; involvement of the upper extremities is less common.3 Patients typically present with a solitary, asymptomatic, firm nodule that had been enlarging in size over a period of several months. Epidermal changes are uncharacteristic, although perforation and ulceration have been reported.4
The diagnosis of pilomatricoma is confirmed by biopsy, which reveals a tumor composed of 2 cell types: Basophilic cells resembling those found in the matrix of hair follicles and faint eosinophilic cells without nuclei termed “shadow cells.”5 Areas of calcification may also be noted. Immunostaining supports a hair follicle origin.6
Definitive treatment of pilomatricoma is accomplished by surgical excision.7 Malignant degeneration is quite rare but has been reported.8
Megha D. Patel is a student at the Commonwealth Medical College, Scranton, Pennsylvania.
Stephen Schleicher, MD, is an associate professor of medicine at the Commonwealth Medical College and an adjunct assistant professor of dermatology at the University of Pennsylvania Medical College. He practices dermatology in Hazleton, Pennsylvania.
- Julian CG, Bowers PW. A clinical review of 209 pilomatricomas. J Am Acad Dermatol. 1998;39(2 Pt 1):191-195.
- Rotenberg M, Laccourreye O, Cauchois R, Laccourreye L, Putterman M, Brasnu D. Head and neck pilomatrixoma. Am J Otolaryngol. 1996;17(2):133-135.
- Schweitzer WJ, Goldin HM, Bronson DM, Brody PE. Solitary hard nodule on the forearm. Pilomatricoma. Arch Dermatol. 1989;125(6):828-829, 832.
- Arnold M, McGuire LJ. Perforating pilomatricoma—difficulty in diagnosis. J Am Acad Dermatol. 1988;18(4 Pt 1):754-755.
- Elder DE, ed. Lever’s Histopathology of the Skin. 9th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004.
- Kizawa K, Toyoda M, Ito M, Morohashi M. Aberrantly differentiated cells in benign pilomatrixoma reflect the normal hair follicle: immunohistochemical analysis of Ca-binding S100A2, S100A3, and S100A6 proteins. Br J Dermatol. 2005;152(2):314-320.
- Morales A, McGoey J. Pilomatricoma: Treatment by incision and curettement. J Am Acad Dermatol. 1980;2(1):44-46.
- Waxtein L, Vega E, Alvarez L, Cortes-Franco R, Hojyo T, Dominguez-Soto L. Malignant pilomatricoma: A case report. Int J Dermatol. 1998;37(7):538-540.