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Features Departments Information |
 Amy S. Paller, MD  Sibel Ersoy, MD |
Dermatology quiz aWinter 2003  A 3-year-old has had a light brown patch on her left arm since birth. The lesion has prominent overlying hairs, shows follicular prominence after the skin is rubbed, and is otherwise asymptomatic. The patient’s past medical history is unremarkable. No one else in the family has any similar lesions. The diagnosis is: Which of the following statements is true? Which of the following is true? Answers: D, A, and A respectively Diagnosis: Congenital smooth muscle hamartoma Discussion: Congenital smooth muscle hamartoma was first described by Stokes and colleagues at the beginning of the century,1 and has an estimated prevalence of 1:1000 to 1:2700 live births.2,3 Smooth muscle hamartoma usually appears at birth or during infancy. Most commonly, it appears as a skin-colored or lightly hyperpigmented patch or plaque on the trunk or extremities.2,4 Hypertrichosis, or prominent overlying hair, is usually present.2,5 Rarely, smooth muscle hamartoma is described as a patch with perifollicular papules without prominent hair. Transient piloerection, or elevation of follicular-based papules within a lesion induced by rubbing (“pseudo-Darier sign”), may be observed.5 In our experience, the pseudo-Darier sign is often absent despite a clear clinical diagnosis. Smooth muscle hamartomas, whether congenital or acquired, have shown no evidence of malignant transformation and do not appear to be associated with other congenital abnormalities.4,5 Histological evaluation of biopsy sections show variably oriented, discrete, hyperplastic smooth muscle bundles within the reticular dermis, sometimes extending to the subcutaneous tissue. Smooth muscle bundles may be associated with hair follicles as well. Masson’s trichrome stain is useful for confirming the smooth muscle nature of the spindle cells, but is usually not necessary for diagnosis. Unlike leiomyomas, smooth muscle bundles do not form a circumscribed tumor. The overlying epidermis may show increased pigmentation of the basal cell layer.5 The differential diagnosis includes Becker’s nevus, congenital pigmented hairy nevus, café au lait spots, and solitary mastocytoma. These lesions are usually not thickened and do not exhibit a positive pseudo-Darier sign. Hypertrichosis is not seen in café au lait spots or solitary mastocytomas. Despite similar histologic findings, a dilemma remains as to whether congenital smooth muscle hamartoma is a distinct entity or a form of Becker’s nevus, which consists of hyperpigmentation, hypertrichosis, and proliferation of smooth muscle, located usually on a shoulder of adolescent males. Becker’s nevus typically appears during childhood or adolescence, and hyperpigmentation usually precedes the hypertrichosis. Congenital smooth muscle hamartoma most commonly shows hypertrichosis with minimal hyperpigmentation and sometimes no hyperpigmentation. The abnormal whorled myofilament pattern in electron microscopic studies of congenital smooth muscle hamartoma is not seen in Becker’s nevus, and further distinguishes these two clinical entities.5 If desired for cosmetic reasons, the hypertrichosis of smooth muscle hamartoma can be cleared by shaving, chemical depilatories or epilative procedures, such as laser epilation or electrolysis. Surgical excision is elective.4 REFERENCES 1. Stokes JH, et al. Nevus pilaris with hyperplasia of nonstriated muscle. Arch Dermatol Syph 1923;7:479-481. 2. Zvulunov A, et al. Congenital smooth muscle hamartoma. Prevalence, clinical findings and follow-up in 15 patients. AJDC 1990;144:782-784. 3. Metzker A, Merlob P. Congenital smooth muscle hamartoma. Letter. J Am Acad Dermatol 1986;14:691. 4. Johnson MD, Jacobs AH. Congenital smooth muscle hamartoma. A report of 6 cases and a review of the literature. Arch Dermatol 1989;125:820-822. 5. Goldman MP, et al. Congenital smooth muscle hamartoma. Int J Dermatol 1987;26:448-452. |