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.


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


Homepage | FAQs | Contact Dr. White

It is not the intention of to provide specific medical advice, diagnosis or treatment. only intends to provide users with information regarding various medical conditions for educational purposes and will not provide specific medical advice. Information on is not intended as a substitute for seeking medical treatment and you should always seek the advice of a qualified healthcare provider for diagnosis and for answers to your individual questions. Information contained on should never cause you to disregard professional medical advice or delay seeking treatment. If you live in the United States and believe you are having a medical emergency call 911 immediately.