Pathology indicated a proliferation of basaloid cells with matrical differentiation in transition and “shadow” cells, pointing to a diagnosis of pilomatricoma.
Pilomatricoma, also known as pilomatrixoma, is a benign skin tumor associated with hair follicles. The lesions are most often found on the neck or head area but can occur on the arms, legs, or torso. They are usually slow growing, solitary, and painless. The frequency of occurrence is rare, accounting for less than 1% of all benign skin tumors.1
A mutation in the Catenin beta-1 (CTNNB1) gene is the most common cause of isolated pilomatricoma and is a somatic defect, meaning it is acquired, not inherited. The mutation of the CTNNB1 gene causes disruption of normal function and maturation of the hair follicle. This leads to rapid cell growth and uncontrolled division, resulting in the formation of the pilomatricoma.1
A comprehensive review performed in 2018 noted that only 16% of pilomatricomas were accurately diagnosed on clinical exam.1 Clues that point to the diagnosis of pilomatricoma are the irregular, whitish yellow spots just under the skin. In contrast, epidermoid cysts usually have a central pore and a ballotable feel. The expression of calcification and gritty material from the lesion in this case ruled out a diagnosis of an epidermoid cyst. The most common method of treatment is surgical removal.1
This patient was counseled regarding her diagnosis and given the option of a plastic surgery referral to excise the affected tissue in its entirety. She opted to wait and see if the growth would scar down and not return.
Image courtesy of Edward A. Jackson, MD. Text courtesy of Edward A. Jackson, MD, FAAFP, Advent Health Medical Group Family Medicine at East Orlando, FL, and Daniel Stulberg, MD, FAAFP, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque.