Discoid Fibromas, Familial Multiple

Description

Familial multiple discoid fibromas (FMDF) is an autosomal dominant dermatologic condition characterized by the appearance of multiple skin-colored, firm, flat or dome-shaped papules on the pinnae and the central area of the face in childhood or adolescence. Most lesions show a hair at or just outside the periphery, and many have a telangiectatic surface (summary by Starink et al., 2012).

Trichodiscoma, as this lesion was first described by Pinkus et al. (1974), is a small benign fibrovascular tumor of the dermal part of the hair disc. The hair disc is a richly vascularized dermal pad in close association with a hair. It is supplied by a thick myelinated nerve and is considered to be a slow-adapting mechanoreceptor. Trichodiscomas are small, flat or dome-shaped, skin-colored, firm papules with a telangiectatic surface. Many of the lesions show a hair at the periphery or just outside it. Starink et al. (2012) renamed the lesion 'discoid fibroma' as a clarification of the histologic findings.

FMDF is similar to, but histologically and genetically distinct from, Birt-Hogg-Dube syndrome (BHD; 135150), which is characterized by fibrofolliculomas as well as renal and pulmonary cysts.

Clinical Features

Starink et al. (1985) described a family in which 7 persons in 3 generations had multiple trichodiscomas with onset of the lesions early in life. Starink et al. (1985) considered the disorder to be distinct from autosomal dominant fibrofolliculomas with trichodiscomas and acrochordons (Birt-Hogg-Dube syndrome).

Starink et al. (2012) evaluated 9 families with familial multiple discoid fibromas, including the family reported by Starink et al. (1985), 3 families previously reported by Leter et al. (2008) as having Birt-Hogg-Dube syndrome (families 11, 17, and 20), 3 families from the same village in the Netherlands, and 2 newly ascertained families. Some of the families were referred for evaluation of suspected Birt-Hogg-Dube syndrome. Most patients showed multiple skin-colored, firm, flat, and dome-shaped papules on the pinnae and the central area of the face; lesions on the trunk and limbs were less common. Most lesions showed a hair at or just outside the periphery; none had a centrally located hair or follicular plug. Lesions were most prominent on the pinnae, and larger lesions showed a telangiectatic surface. Onset was usually in childhood or early adolescence. Histologic studies showed well-circumscribed elliptical (or discoid) fibrovascular tumors with a flattened overlying epidermis and a peripheral bent hair follicle. Some lesions showed coarse hyalinized collagen bundles in a whorled pattern. Strands of basaloid epithelial cells extending from a central follicular infundibulum, characteristic of fibrofolliculomas, were notably absent in all biopsy specimens.

Inheritance

Starink et al. (1985) described a family in which 7 persons in 3 generations had multiple trichodiscomas in a pattern consistent with autosomal dominant inheritance.

Molecular Genetics

Exclusion Studies

Starink et al. (2012) excluded pathogenic mutations in the FLCN gene (607273) in 9 families with familial multiple discoid fibromas. In addition, linkage to the FLCN gene was excluded in 2 of the affected families.

Nomenclature

Starink et al. (2012) renamed the lesion 'discoid fibroma' and the condition 'familial multiple discoid fibromas' (FMDF) to emphasize the distinction from BHD and the fibrofolliculoma/trichodiscoma spectrum in BHD.