Cutaneous smooth muscle tumors

Slight male predominance

Prevalence of 1 in about 2700 live births

The majority of the lesions are congenital

Familial occurrence exceptional, with autosomal-dominant inheritance reported in some families

Skin-colored indurated patch, plaque, follicular papules, or variably pigmented macules; occasionally associated with hypertrichosis

Usually asymptomatic, but can be pruritic

Stroking of the lesion can result in transient elevation of the affected area and piloerection due to smooth muscle contraction (pseudo-Darier sign)

Induration, hyperpigmentation, and hypertrichosis diminish over time

Unusual clinical presentations include linear, atrophic, or a morphea-like plaque

Multiple lesions or a generalized presentation very rare

The generalized variant occasionally part of the “Michelin-tire baby” syndrome, characterized by deep circumferential skin folds over the trunk and limbs with distinctive clinical appearance, mental retardation, and other developmental abnormalities

Predilection for lumbosacral area and proximal extremities

Uncommon sites include the head and neck, conjunctiva, nipple, and genital area

Rare associated conditions include Becker nevus, congenital melanocytic nevus, and basal cell carcinoma, with the latter two conditions likely to be coincidental

No treatment generally required

Surgical excision or laser treatment usually for cosmetic reasons

Localized in the dermis, with occasional extension into the subcutis

Mature smooth muscle cells, growing in haphazardly arranged bundles

Mitotic activity absent

Association with morphologically normal hair follicles in about 40%

Prominent nerve fibers and collagen bundles usually present among smooth muscle bundles

Overlying epidermis normal or displays mild hyperkeratosis, acanthosis, and hyperpigmentation of basal keratinocytes

Smooth muscle actin, calponin, desmin, and h-Caldesmon positive

Becker nevus

Pilar leiomyoma (more orderly proliferation of smooth muscle bundles arranged in ramifying fascicles, intervening collagen more discrete)

Most commonly develops in the second and third decades of life

Female predominance for multiple lesions, whereas solitary tumors occur more commonly in males

Congenital occurrence exceptional, likely overlapping with or representing a variant of congenital smooth muscle hamartoma

A subset of pilar leiomyoma(s) occurs in the familial setting, the so-called Reed syndrome or multiple leiomyomatosis

• Autosomal-dominant mode of inheritance

• Associated with germline mutation(s) of the fumarate hydratase ( FH ) gene on chromosome 1q42.3-43 acting as a tumor suppressor gene

• Combination of multiple pilar and uterine leiomyomas, additionally complicated by development of a solitary multifocal or bilateral papillary renal cell carcinoma in roughly up to 20% of patients

Firm and smooth, skin-colored, red-brown to violaceous papule(s) or nodule(s)

Multiple lesions

• More common than solitary lesions

• Size of individual lesion usually up to 1 cm in diameter

• Often tender or painful, either spontaneously or in response to cold, pressure, or emotional stimuli

• Show predilection for extensor surface(s) of the extremities and trunk

• Distribution can be segmental, dermatomal, linear, zosteriform, or more widespread/diffuse

Solitary lesions

• Most commonly develop on the limbs

• Tend to be larger than multiple tumors

• Frequently asymptomatic

• Rarely presentation may be with an indurated plaque

Complete surgical excision curative, but difficult to achieve in multiple tumors

Recurrence rate as high as 50% for multiple lesions

Dermal-based proliferation, extension into the subcutis infrequent

Poorly circumscribed and infiltrative, less often nodular and well circumscribed

Interweaving/interlacing fascicles of bland spindle cells displaying typical features of smooth muscle differentiation

• Cigar-shaped or blunt-ended nuclei

• Low mitotic activity present in roughly 30% of the lesions (fewer than 1 mitosis per 10 high-power fields)

• Bright eosinophilic cytoplasm

Histological variants

• Epithelioid

• Symplastic

  • Pleomorphic cells with large, multilobated, hyperchromatic nuclei; macronucleoli; and intranuclear cytoplasmic pseudoinclusions, usually scattered among bland spindle cells

  • Multinucleated giant cells not uncommon

  • Mitotic activity low (usually fewer than 1 per 10 high-power fields)

  • Necrosis absent

  • Represents degenerative phenomenon

Positive for smooth muscle actin, desmin, calponin, and h-Caldesmon

A small percentage of cases express keratin

Cutaneous leiomyosarcoma

Metastatic leiomyosarcoma

Cellular dermatofibroma

Dermatofibrosarcoma protuberans with myoid nodules

Predilection for middle-aged adults

Solitary, slowly growing papule or nodule, less often a pedunculated lesion with surface ulceration

Multiple lesions most uncommon

Lesions can increase in size during pregnancy

Most of the lesions are asymptomatic

Nipple leiomyomas

• Tend to be smaller (generally less than 2 cm)

• Poorly circumscribed

Vulvar and scrotal leiomyomas

• Size generally between 3 and 5 cm in diameter

• Well circumscribed

Vulvar leiomyoma(s) can be associated with synchronous or metachronous development of esophageal leiomyoma(s), a condition known as esophagovulvar syndrome

Complete surgical excision curative

Histological features essentially similar to pilar leiomyomas, including the so-called symplastic change representing a degenerative phenomenon (see corresponding section on pilar leiomyoma)

Certain morphological features occur more commonly at genital sites (see below)

Vulvar and scrotal leiomyomas

• More cellular than pilar leiomyomas

• Tend to be better circumscribed and more nodular but not encapsulated

• Focal or more widespread epithelioid morphology common

• Myxoid change frequent, especially during pregnancy

• Hyalinization of the stroma can be prominent

• Variably intense perivascular inflammatory cell infiltrate composed of lymphocytes, histiocytes, and eosinophils

Smooth muscle actin, calponin, desmin, and h-Caldesmon positive

Variable positivity (over 50%) for estrogen and progesterone receptors

Androgen receptor positivity in scrotal leiomyomas

No consistent cytogenetic change in vulvar leiomyomas, yet the data is limited

Angiomyofibroblastoma

Aggressive angiomyxoma