DermDx: Small Nodule on Shin

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A 55-year-old man presents to the clinic requesting removal of a growth on his lower left leg. The lesion has been present for approximately a year and has remained asymptomatic. The patient is in good health and takes no oral medications. Examination reveals a firm, slightly erythematous nodule of the left lateral tibial area with a crusted center. No similar lesions are noted elsewhere.

Pilomatricoma, also referred to as calcifying epithelioma of Malherbe, is a benign hair follicle tumor derived from hair matrix cells.1 The neoplasm most commonly arises in children and is found primarily on hair-bearing areas such as the head, neck, and...

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Pilomatricoma, also referred to as calcifying epithelioma of Malherbe, is a benign hair follicle tumor derived from hair matrix cells.1 The neoplasm most commonly arises in children and is found primarily on hair-bearing areas such as the head, neck, and upper extremities.2 Lesions present as well-circumscribed, flesh-colored to bluish firm nodules that are usually less than 3 cm in diameter. Histology reveals a combination of ghost cells, shadow cells, basophilic cells, and calcifications. A majority of cases have somatic mutations in the CTNNB1 gene, which encodes a protein involved with regulation of cell growth and attachment.3 Malignant transformation of pilomatricomas is rare.4

Several variants of pilomatricoma have been described including anetodermic, bullous, aggressive, superficial, proliferating, cystic, pseudocystic, pigmented, acantholytic, and ossifying.5 Perforating pilomatricoma is an uncommonly encountered subtype that presents as a crusted or ulcerated nodule.6 Lesions may resemble inflammatory papules, cutaneous horn-like nodules, and keratoacanthomas. Preferred treatment of all variants is surgical excision.

Britany Spinosa-Weber, PA-C, is on staff at the DermDox Dermatology Center in Bethlehem, Pennsylvania. Stephen Schleicher, MD, is director of the DermDox Dermatology Centers, associate professor of medicine at Geisinger Commonwealth Medical College, and clinical instructor of dermatology at Arcadia University and Kings College.

References

1.  Thompson LD. Pilomatricoma. Ear Nose Throat J. 2012;91(1):18-20. doi:10.1177/014556131209100106

2. Schwarz Y, Pitaro J, Waissbluth S, Daniel SJ. Review of pediatric head and neck pilomatrixoma. Int J Pediatr Otorhinolaryngol. 2016;85:148-153. doi:10.1016/j.ijporl.2016.03.02

3. Lazar AJ, Calonje E, Grayson W, et al. Pilomatrix carcinomas contain mutations in CTNNB1, the gene encoding beta-catenin. J Cutan Pathol. 2005;32(2):148-157. doi:10.1111/j.0303-6987.2005.00267.x

4. Kondo T, Tanaka Y. Malignant pilomatricoma in the parietal area. Pathol Oncol Res. 2006;12(4):251-253. doi:10.1007/BF02893423

5. Sung KY, Lee S, Jeong Y, Lee SY. Ossifying pilomatricoma and a novel hypothesis for its pathogenesis: a case report and comprehensive literature review. Medicine (Baltimore). 2022;101(6):e28753. doi:10.1097/MD.0000000000028753

6. Thakur BK, Verma S, Mishra J. Perforating pilomatricoma in a 62-year-old female: a rare case report. Int J Trichology. 2014;6(4):173-174. doi:10.4103/0974-7753.142864

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