CONGENITAL SMOOTH MUSCLE HAMARTOMA
By Gary M. White, MD
Congenital smooth muscle hamartoma (CSMH) is a benign cutaneous lesion caused by an overabundance of mature smooth muscle fibers in the dermis.
- Zvulunov et al estimated its prevalence to be approximately 1:2600 live births[AJDC 1990;144;782].
- CSMH and Becker Nevus are thought to be variants of the same hamartomatous process.
A slightly pigmented, hypertrichotic area on the trunk or extremities is characteristic. Stroking of the lesions causes contraction of the smooth muscle bundles resulting in induration or piloerection, the so called "pseudo Darier's sign". The lumbosacral location is the preferred site. Rarely, other clinical appearances may be seen, e.g. a patch with perifollicular papules, vermiform movements, a congenital linear, reddish, atrophic plaque [PD 1996;13;222], or Michelin tire baby.
No treatment is indicated as lightening of the color and reduction of the hypertrichosis usually occur over time.
Congenital, hypertrichotic plaques. Indian Journal of Dermatology Jan-Mar 2009
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