Smooth muscle hamartoma

smooth muscle hamartoma 4

Smooth muscle hamartoma is a benign skin condition histologically characterized by localized overgrowth of smooth muscle bundles in the dermis. Clinically, it appears as flesh-colored, occasionally pinkish-brown patches or flat plaques covered with light downy or long dark hairs. ICD-10 Code: Q85.9

Congenital and acquired forms of smooth muscle hamartoma are distinguished. In the vast majority of cases, the condition is congenital and occurs with a frequency of 1 in 2600 births, with a slight predominance of males over females in a ratio of 1.5:1. Almost all reported cases have been sporadic, except for rare observations of multiple hamartomas in members of the same family, suggesting a possible genetic predisposition.

The etiology and pathogenesis of this disorder remain unknown. Congenital smooth muscle hamartoma probably results from abnormal proliferation of arrector pili muscle cells during fetal mesodermal maturation. In rarer cases, proliferation of cells from the tunica dartos and blood vessels has been noted.

Some studies have shown a significant increase in the number of CD34-positive dendritic cells in the reticular dermis. It has been suggested that they may play a role in the aberrant development of the arrector pili muscles and stimulate hypertrichosis in the affected areas.

Cases of smooth muscle hamartoma coexisting with Becker nevus have been described. Controversy remains as to whether Becker's nevus and congenital smooth muscle hamartoma are variations of the same condition or distinct nosologic entities.

Typical smooth muscle hamartoma

smooth muscle hamartoma 1

Characterized by a well-defined, irregularly shaped lesion in the form of a patch or flat infiltrated plaque, usually flesh-colored or pink-brown, ranging in size from 1 to 10 cm, occasionally larger. The surface of the lesion is covered with either light downy or long dark hairs. In some cases, there may be flesh-colored papules around the hair follicles along with the hypertrichosis (mixed form). Darier's sign is positive in almost all cases.

The lesion is usually solitary and most commonly located on the skin of the lumbosacral region, buttocks, and proximal parts of the limbs. Less commonly, lesions may be found in atypical locations such as the scrotum, scalp, cheeks, soles, elbows, eyelids, nipples, vulva, and conjunctiva.

With age, congenital smooth muscle hamartoma increases in size in proportion to the child's growth, while hyperpigmentation and hypertrichosis tend to decrease. In some cases, the eruptions resolve completely.

Papulo-follicular smooth muscle hamartoma

smooth muscle hamartoma papulo-follicul
Occurs less frequently. It is characterized by lesions in the form of numerous perifollicular, skin-colored papules that tend to coalesce into irregularly shaped plaques. The hair component is usually not prominent or may be absent. Darier's sign is often positive.

Linear Smooth Muscle Hamartoma

smooth muscle hamartoma 2 linear
A rare form of hamartoma characterized by a cluster of perifollicular and polypoid papules of soft consistency, flesh-colored, with light downy hairs, arranged in a linear pattern. It is predominantly located on the head (especially the chin area) and neck. Some cases have been reported to follow the lines of Blaschko. Darier's sign is often positive.

Atrophic smooth muscle hamartoma

smooth muscle hamartoma atrophic
An extremely rare form of the disease. Only two cases have been described (one acquired and one congenital smooth muscle hamartoma). It presents as a depressed, atrophic, infiltrated, and hyperpigmented irregularly shaped plaque. Hypertrichosis and Darier's sign were absent in the affected area.

Generalized smooth muscle hamartoma

smooth muscle hamartoma general
The generalized (diffuse) form of congenital smooth muscle hamartoma is extremely rare. Clinically, it is characterized by multiple, large, flesh-colored to tan patches and plaques with diffuse hypertrichosis and excessive skin folding. It is associated with Michelin tire syndrome in children, which is often associated with systemic disorders such as skeletal and facial anomalies, growth retardation, mental retardation, underdeveloped joints, seizures, inguinal hernias, and pigmentary retinopathy.

Acquired smooth muscle hamartoma

smooth muscle hamartoma acquired
Reported cases have been observed in patients 16 to 64 years of age. Clinical manifestations are usually similar to those of congenital smooth muscle hamartoma, but differ in unusual localization (often in the genital area - scrotum, vulva), mild hypertrichosis, and a negative Darier's sign.

Diagnosis is based on the patient's history, clinical presentation, the presence of Darier's pseudo-sign, and the results of histologic examination.

Darier's pseudo-sign:

A characteristic clinical feature of congenital smooth muscle hamartoma is a positive Darier's pseudo-sign, which occurs in more than 80% of cases.

When the affected areas are rubbed or exposed to cold/heat, temporary induration, enlargement, whitening/redness, and piloerection are observed. This is due to mechanical stimulation of the arrector pili muscles, not histamine release as in true Darier's sign.

Dermoscopy:

Dermoscopy is used to assess hair density in congenital smooth muscle hamartoma because it has been found that hair density is proportional to the number of smooth muscle bundles in the affected areas.

  • Congenital Melanocytic Nevi
  • Becker Nevus
  • Leiomyomas
  • Solitary Mastocytoma
  • CafĂ© au lait macules
  • Morphea

Treatment for smooth muscle hamartoma is based primarily on cosmetic indications. Here are some of the treatment options:

  • Surgical excision: Surgical removal of the lesion is a common treatment option, but some authors do not recommend it because of the risk of scarring or other cosmetic concerns.
  • Laser hair removal: Laser therapy may be used to remove excess hair from affected areas.
  • Dye laser treatment: Dye laser treatment may be considered for erythematous lesions.

The prognosis for smooth muscle hamartoma is generally good.