An Atlas of Lumps and Bumps: Part 11

AUTHORS:
Alexander K. C. Leung, MD^1,2 —Series Editor • Benjamin Barankin, MD³ • Joseph M. Lam, MD⁴ • Kin Fon Leong, MD⁵

AFFILIATIONS:
¹Department of Pediatrics, University of Calgary, Calgary, Alberta, Canada
²Alberta Children’s Hospital, Calgary, Alberta, Canada
³Toronto Dermatology Centre, Toronto, Ontario, Canada
⁴Department of Pediatrics and Department of Dermatology and Skin Sciences, University of British Columbia, Vancouver, British Columbia, Canada
⁵Pediatric Institute, Kuala Lumpur General Hospital, Kuala Lumpur, Malaysia

CITATION:
Leung AKC, Barankin B, Lam JM, Leong KF. An atlas of lumps and bumps, part 11. Consultant. 2021;61(21):e21-e23. doi:10.25270/con.2021.11.00006

DISCLOSURES:
Dr Leung is the series editor. He was not involved with the handling of this paper, which was sent out for independent external peer review.

CORRESPONDENCE:
Alexander K. C. Leung, MD, #200, 233 16th Ave NW, Calgary, AB T2M 0H5, Canada (aleung@ucalgary.ca)

EDITOR’S NOTE:
This article is part of a series describing and differentiating dermatologic lumps and bumps. To access previously published articles in the series, visit https://bit.ly/35J1I1v.

Pilomatricoma

A pilomatricoma, also known as pilomatrixoma or calcifying epithelioma of Malherbe, is a benign adnexal subcutaneous tumor derived from primitive epidermal germ cells differentiating toward hair matrix cells.¹ Pilomatricomas account for approximately 1% of all benign skin nodules/cysts in childhood.² The peak age of onset is in the first 2 decades of life and again between age 50 and 65 years.^1-5 The female to male ratio is approximately 2:1.² The condition is more common in White individuals than Asian individuals.⁶ Pilomatricomas can be familial.² Activating mutations in β-catenin have been identified in approximately 75% of patients with pilomatricomas.⁷ The locus of this tumor has been mapped to the CTNNB1 gene on 3p22-p21.3.^3,7

Typically, a pilomatricoma presents as a firm to hard, solitary, painless nodule in the subcutaneous tissue (Figures 1 to 5).^1,2  It is usually freely-mobile but slightly attached to the overlying skin.⁸ The color of the overlying skin varies from flesh-colored, pink, erythematous, blue, red-blue, to blue-black.^7,9 The size of the lesion is usually 0.5 to 3.0 cm in diameter, although a lesion measuring 34 cm has been reported.¹⁰ Most lesions increase in size slowly over a period of months to years and then stabilize.^1,11 Rapidly growing pilomatricomas have rarely been reported. The nodule may become hardened if the lesion is calcified. Calcification and ossification occur in 70% to 85% and 15% to 20% of patients, respectively.¹ Downward pressure directed at one end of the lesion may cause the other end to protrude from the skin (“teeter-totter” sign) (Figure 6).⁸ Multiple facets and angles may appear when the overlying skin is stretched (“tent” sign, Figure 7).^2,3,8,12 Pilomatricoma most commonly occur on the head (particularly, the face) and neck, followed by upper extremities, trunk, and lower extremities.^2,4,11 The majority of cases are asymptomatic, although some patients may report pain or pruritus.²

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

 
Figure 7.

Several clinical variants have been recognized. In the pseudobullous or anetodermic variant, the lesion is bullous-looking, and the overlying skin is atrophic, translucent, pink, or erythematous (Figure 8).⁷ Telangiectasis may be seen. The tumor is rapidly growing. Sites of predilection include the upper arms and shoulders.¹³ A pseudobullous or anetodermic pilomatricoma can be depressed at the center when vertical pressure is applied (dimple sign).¹³ Rarely, a pilomatricoma may rupture, resulting in an ulcerated or crusted nodule; this variant is referred to as perforating pilomatricoma (Figure 9).^4,7 A pilomatricomal horn is a superficial variant of pilomatricoma.¹⁴ Giant pilomatricoma is another clinical variant, arbitrarily defined as a lesion greater than 5 cm.⁷

Figure 8.

Figure 9.

Most cases are sporadic. Multiple pilomatricomas occur in 2 to 5% of cases.¹ The presence of 6 or more pilomatricomas is highly suggestive of an underlying disorder such as Gardner syndrome, Turner syndrome, Rubinstein-Taybi syndrome, Kabuki syndrome, Churg-Strauss syndrome, basal cell naevus syndrome (Gorlin syndrome), Soto syndrome, constitutional mismatch repair deficiency (CMMR-D), myotonic dystrophy, xeroderma pigmentosum, sarcoidosis, or trisomy.^{7,9,11,12,15-18} Although pilomatricoma is generally benign, malignant transformation has been, very rarely, described.^19,20