Becker's nevus

Congenital Smooth Muscle Hamartoma In human skin, smooth muscle is limited to the walls of cutaneous blood vessels, the dartos tunica, the areolae, the hair follicles and limited areas of the face and extremities (cutis diagonales muscles). Smooth muscle tissue is predominant in hair follicles, forming the arrectores pilorum muscles.

Congenital smooth muscle hamartomas develop during fetal life, at the time of mesoderm maturation. Other cutaneous smooth muscle tumors, such as leiomyoma, angiomyoma and leiomyosarcoma, also arise from the arrector muscles. Clinically, smooth muscle hamartomas can be mistaken for such lesions as congenital nevocellular nevi and Becker's melanosis.

Illustrative Case

A healthy infant boy had a slightly raised, skin-colored plaque over the left buttock at birth. No history of birth trauma or prenatal exposure to x-rays, alcohol or drugs was elicited, and no other abnormalities were noted.

Physical examination revealed a slightly raised, skin-colored plaque that measured approximately 2 by 3 cm and was located over the patient's left buttock and lumbar area (Figure 1). The borders of the lesion were irregular but distinct. Light rubbing of the lesion were irregular but distinct. Light rubbing of the lesion resulted in worm-like movements, which progressed in a wave over the entire lesion and were accompanied by transient elevation and increased firmness of the lesion (Figure 2).

Punch biopsy showed abundant, well-circumscribed bundles of smooth muscle within the reticular dermis but not associated with hair follicles. Masson (trichrome) stain confirmed that the bundles were smooth muscle fibers.

Clinical Findings

Congenital smooth muscle hamartoma is an uncommon, benign entity characterized by proliferation of arrector muscles within the reticular dermis. The lesion is usually apparent at birth, or is noted shortly thereafter, and presents as a skin-colored or slightly hyperpigmented macule or plaque, most commonly on the trunk or upper extremities. The lesion is sharply demarcated and may contain prominent vellus hairs, which are longer and thicker than the hairs in the surrounding skin. In older patients, the lesion may contain prominent perifollicular papules. Transient firmness or elevation of the lesion is noted when the lesion is rubbed (pseudo-Darier's sign). Less commonly, vermiform (worm-like) movements have been described.

Histologic Findings

The predominant histologic feature of congenital smooth muscle hamartoma is well-circumscribed, variably oriented hyperplasia of smooth muscle bundles within the reticular dermis. Occasionally, these bundles extend into the subcutaneous fat. Confirmation of the smooth muscle origin of the tumor can be achieve with special stains, such as Masson stain or phosphotungstic acid-hematoxylin stain. Increased epidermal pigment is noted in specimens of hyperpigmented lesions.

Pathogenesis

The word "hamartoma" literally means" a mass of tissue gone bad." The term denotes a malformation characterized by an abnormal mixture of nonneoplastic tissue elements that are normally indigenous to a given organ, with an excess of one or more of these tissue elements. In the skin, hamartomatous development may occur in the epidermis, appendages, dermis and/or subcutaneous tissue. Congenital smooth muscle hamartoma represents a dysplasia in the development of pilar smooth muscle (arrectores pilorum) during fetal maturation. Although congenital smooth muscle hamartoma is generally considered a rare condition, it may be more common than the literature suggests. Because of a lack of awareness of this entity, it may be mistaken for other dermatologic conditions.

The pseudo-Darier's sign has been described by Nickel. Local stimulation results in impulses conducted by nerves, with resultant smooth muscle contraction and transient elevation or rippling movements of the lesion. The movements suggest coordinated smooth muscle contraction.

Differential Diagnosis

Clinical diagnosis of congenital smooth muscle hamartoma is difficult because of the lack of specific diagnostic criteria. These lesions often have a striking similarity to other conditions. The differential diagnosis includes epidermal nevi, solitary mastocytoma, pilar leiomyoma, connective tissue nevi, Becker's melanosis and congenital melanocytic nevi.

Epidermal nevi are often present at birth and may be confused clinically with congenital smooth muscle hamartoma. However, microscopic examination of epidermal nevi shows hyperplasia of the epidermis and papillary dermis, without smooth muscle proliferation. Surgical excision of the lesion is the treatment of choice. Cryotherapy may also be satisfactory, although recurrences are common following this method of treatment.

Solitary mastocytoma appears as a yellow-brown nodule, caused by mast cell proliferation. When rubbed or traumatized, the lesion becomes erythematous, raised and pruritic (Darier's sign) as a result of the release of histamine by the mast cells. If Darier's sign is ambiguous, the presence of many mast cells on histologic examination confirms the diagnosis of mastocytoma. Histamine-filled granules are evident on Giemsa stain. Most mastocytomas resolve spontaneously before puberty, and excision is usually not necessary.

Pilar leiomyoma may be confused with congenital smooth muscle harmartoma, both clinically and histologically. Although sometimes congenital, pilar leiomyomata usually develop during adolescence or early adult life, most commonly on the face, trunk and extremities. Nodular lesions may coalesce to form yellow or brown plaques. A helpful clinical point of differentiation from congenital smooth muscle hamartoma is that larger, more developed lesions of pilar leiomyoma are often painful or pruritic because the tumor is impinging on cutaneous nerves.

As with congenital smooth muscle hamartomas, pilar leiomyomata may demonstrate pseudo-Darier's sign. This phenomenon occurs because, like congenital smooth muscle hamartoma, pilar leiomyomata arise from arrectores pilorum muscles. However, they are histologically distinct from congenital smooth muscle hamartoma. In pilar leiomyomata, the smooth muscle bundles are aggregated and without capsule or organization, whereas in congenital smooth muscle hamartomas the smooth muscle bundles are well defined and extend in different directions.

Connective tissue nevi (connective tissue hamartomas) are usually present at birth. They are most common on the chest, back, buttocks and upper extremities and may appear as individual papules or plaques. A perifollicular arrangement may be evident, giving the lesion a cobblestone appearance. It is important to diagnose these lesions, because connective tissue nevi may be familial and may be associated with systemic disease, although most are not. Connective tissue nevi of the collagen type may appear as the shagreen patch of tuberous sclerosis, and patients found to have collagen-type connective tissue nevi should be carefully examined for other signs of tuberous sclerosis.

Buschke-Ollendorff syndrome (dermatofibrosis lengticularis disseminata) is characterized by the presence of connective tissue nevi of the elastic type and osteopoikilosis (a hereditary dysplasia affecting the long bones and the bones of the hands, feet and pelvis). The radiographic picture of osteopoikilosis is often confused with osseous metastases.

Connective tissue nevi of the proteoglycan type are often associated with the dermal nodules that accompany mucopolysaccharidosis Type II (Hunter's syndrome). Biopsy shows diffuse proliferation of connective tissue stroma throughout the dermis. Special stains are required to determine the particular type of connective tissue involved in the lesion.

Becker's melanosis may closely resemble congenital smooth muscle hamartoma. An acquired lesion, Becker's melanosis is most commonly seen as a hyperpigmented, hypertrichotic lesion on the shoulder or chest of an adolescent or adult male. The hair within and surrounding the hyperpigmented area is usually dark and coarse. These thick terminal hairs differ from the fine vellus hairs seen in congenital smooth muscle hamartoma. Accentuation of macular perifollicular pigment may also distinguish Becker's melanosis from congenital smooth muscle hamartoma, which exhibits follicular papules but not pigmentary papules. Histologically, Becker's melanosis frequently exhibits smooth muscle proliferation within the dermis, but the presence of increased numbers of melanocytes, acanthosis and rete ridge elongation clearly distinguish this lesion from congenital smooth muscle hamartoma.

Congenital melanocytic nevi are present in approximately 1 percent of all newborns. They appear as pigmented and slightly elevated lesions with mild to moderate hair growth. Because these lesions (even those less than 10 cm in diameter) are known to have malignant potential, surgical excision is often recommended. They can easily be distinguished from congenital smooth muscle hamartoma histologically by the presence of typical nevus cells and the absence of smooth muscle hyperplasia in the dermis. Biopsy of all pigmented lesions is recommended before surgical excision, since inadvertant excision of a congenital smooth muscle hamartoma masquerading as a congenital melanocytic nevus would be of no therapeutic value and might result in permanent disfigurement.

Final Comment

Some authors propose that congenital smooth muscle hamartoma lies at one end of a spectrum of dermal smooth muscle proliferation disorders. Becker's melanosis is at the other end of the continuum. 8,21,22 A prolonged follow-up of congenital smooth muscle hamartoma may better reveal its relationship to Becker's melanosis and to various other organoid hamartomas of the skin. Greater awareness of this condition will undoubtedly bring to light many new cases. REFERENCES 1. Montgomery H, Winkelmann RK. Smooth-muscle tumors of the skin. Arch Dermatol 1959; 79:32-41. 2. Hanke CW, O'Brian JJ, Peters WC, Horney DA, Logan PC. congenital smooth muscle hamartoma masquerading as congenital pigmented nevus. J Dermatol Surg Oncol 1985; 11:714-7. 3. Berger TG, Levin MW. Congenital smooth muscle hamartoma. J Am Acad Dermatol 1984; 11(4 Pt 2): 709-12. 4. Goldman MP, Kaplan RP, Heng MC. Congenital smooth muscle hamartoma. Int J Dermatol 1987; 26: 448-52. 5. Tsambaos D, Orfanos CE. Cutaneous smooth muscle hamartoma. J Cutan Pathol 1982; 9: 33-42. 6. Dupre A, Viraben R. Congenital smooth muscle nevus with follicular spotted appearance (Letter). J Am Acad Dermatol 1985; 13 (5 Pt 1): 837-8. 7. Berberian BJ, Burnett JW. Congenital smooth muscle hamartoma: a case report. Br J Dermatol 1986; 115: 711-4. 8. Slifman NR, Harrist TJ, Rhodes AR. Congenital arrector pili hamartoma. A case report and review of the spectrum of Becker's melanosis and pilar smooth-muscle hamartoma. Arch Dermatol 1985;121:1034-7. 9. Truhan AP, Esterly NB. Hypertrichotic skin-colored patches in an infant. Congenital smooth-muscle hamartoma (CSMH). Arch Dermatol 1985; 121: 1197, 1200-1. 10. Metzker A, Amir J, Rotem A, Merlob P. Congenital smooth muscle hamartoma of the skin. Pediatr Dermatol 1984; 2: 45-8. 11. Kern F, Hambrick GW Jr. Smooth muscle hamartoma. Birth Defects 1971; 7: 346-7. 12. Bronson DM, Fretzin DF, Farrell LN. Congenital pilar and smooth muscle nevus. J Am Acad Dermatol 1983;8:111-4. 13. Willis RA. The borderland of embryology and pathology. 2d ed. Washington, D.C.: Butterworth 1962;351. 14. Fine HL, Possick PA, Myrow RE. Transient rippling of the skin: smooth muscle hamartoma? [Letter] Arch Dermatol 1974;110:141. 15. Nickel WR. Abstract of discussion in Montgomery and Winkelmann. Smooth muscle tumors of the skin. Arch Dermatol 1959;79:41. 16. Stokes JH. Nevus pilaris with hyperplasia of nonstriated muscle. Arch Dermatol 1923;7:479-81. 17. Chapel TA, Tavafoghi V, Mehregan AH, Gagliardi C. Becker's melanosis: an organoid hamartoma. Cutis 1981; 27:405-6,410,415. 18. Urbanek RW, Johnson WC. Smooth muscle hamartoma associated with Becker's nevus. Arch Dermatol 1978; 114:104-6. 19. Haneke E. The dermal component in melanosis naeviformis Becker. J Cutan Pathol 1979;6:53-8. 20. Illig L, Weidner F, Hundeiker M, et al. Congenital nevi less than or equal to 10 cm as precursors to melanoma. 52 cases, a review, and a new conception. Arch Dermatol 1985;121: 1274-81. 21. Wong RC, Solomon AR. Acquired dermal smooth-muscle hamartoma. Cutis 1985;35:369-70. 22. Karo KR, Gange RW. Smooth-muscle hamartoma. Possible congenital Becker's nevus. Arch Dermatol 1981;117:678-9.

PHOTO : FIGURE 1.Congenital smooth muscle hamartoma over the left buttock and lumbar area.

PHOTO : FIGURE 2.Light rubbing causes worm-like movements, transient elevation and increased firmness of the lesion.

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