Description

• Benign, adnexal skin tumor derived from hair matrix cells
• Slow-growing, hard, typically solitary nodule found in the dermis/subcutaneous layer of the skin
• Most commonly occurs on the head and neck of children and young adults (1)
• Variants:
  • Pilomatrix carcinoma, a rare malignant variant, can be locally invasive and have a high recurrence rate. Infrequent cases of metastases have been reported.
  • Perforating pilomatricoma
• Synonym(s): pilomatrixoma; calcifying epithelioma of Malherbe; trichomatricoma
• System(s) affected: integumentary

Epidemiology

Incidence

• Pilomatricoma was first described in 1880 by Malherbe and Chenantais (2).
• Incidence of pilomatricomas has not been well studied.
• One study reported an incidence of 1.04% of all benign skin tumors examined and 0.08% of all histologic samples reviewed.
• Slight female preponderance (male-to-female ratio, 1:1.1)
• Most frequently occurs in patients <20 years old (37–46%), with some reports of a second smaller peak in the 5th to 7th decades of life

Etiology and Pathophysiology

• Pilomatricomas derive from the primitive basaloid cells of the epidermis that differentiate into hair matrix cells with uncontrolled proliferation in the dermis/subcutaneous tissue
• There are anecdotal reports of lesions arising in areas of trauma, insect bites, and surgery (3.9% of cases).

Genetics

• Activating β-catenin gene (CTNNB1) mutations are thought to play an important role.
• A high level of β-catenin results in the stimulation of cellular proliferation and/or inhibition of cell death.

Risk Factors

No known risk factors

Commonly Associated Conditions

Although uncommon, multiple pilomatricomas have been associated with the following conditions:

• Myotonic dystrophy
• Turner syndrome
• Rubinstein-Taybi syndrome
• Trisomy 19
• Sotos syndrome
• Gardner syndrome