What is a leiomyoma?

A leiomyoma is a benign tumour composed of smooth muscle. It is capable of arising wherever smooth muscle is present. One form of leiomyoma arises from uterine smooth muscle, and is otherwise known as uterine fibroids.  

Cutaneous leiomyomas may be classified into three types:

• Piloleiomyoma
• Angioleiomyoma
• Genital leiomyoma

Each type arises from smooth muscle in specific tissues or organs and has distinct clinical or histological features.

Piloleiomyoma

• Originates from the arrector pili muscle of the pilosebaceous unit  
• Solitary or multiple lesions
• Multiple lesions may occur sporadically or are inherited alongside uterine fibroids in an autosomal dominant pattern as part of hereditary leiomyomatosis and renal cell cancer syndrome or as part of Reed syndrome (multiple cutaneous and uterine leiomyomatosis)

Angioleiomyoma

• Originates from vascular wall smooth muscle tissue
• Typically occurs as a solitary lesion

Genital leiomyoma

• Originates from the dartos muscle in the scrotum or labium major, or from erectile muscle in nipples
• Typically occurs as a solitary lesion
• Least common of the cutaneous leiomyoma

Who gets leiomyomas?

Uterine leiomyomas represent 95% of all reported leiomyomas. Cutaneous leiomyomas represent 75% of all extra-uterine leiomyomas.

• Incidence is largely unrelated to race.
• The majority of solitary ­cutaneous leiomyomas occur in adulthood. Multiple piloleiomyomas typically occur between the ages of 10 and 30 years.
• Excluding autosomal dominant syndromes, piloleiomyoma incidence is equal in men and women. Angioleiomyomas are generally more common in women than men (2:1) although cavernous and venous subtypes are more common in men.

What are the clinical features of leiomyomas?

Leiomyomas are often painful.

• Pain may be spontaneous or triggered by physical and/or emotional stimuli, including cold temperature or pressure. Menses or pregnancy may also act as triggers

Piloleiomyomas

• Likely to present with associated pain
• Typically tender, mobile hyperpigmented or reddish brown nodules (≤ 2cm diameter) with a smooth surface and firm consistency
• Solitary lesions typically in the lower extremities while multiple piloleiomyomas appear anywhere in a variety of distribution patterns

Angioleiomyomas

• 60% reported to be painful
• Tenderness is less common than in piloleiomyomas
• Well circumscribed, skin coloured, solitary nodules ≤ 4cm in diameter usually found on the lower legs. Uncommonly on head, trunk, hands or mouth.

Genital leiomyomas

• Typically non-tender and painless
• Firm, solitary, skin coloured, mobile nodule on the vulva, scrotum or nipple. Size is more variable than other types; vulval and scrotal lesions are typically larger.

Leiomyomas

How are cutaneous leiomyomas usually diagnosed?

Cutaneous leiomyomas are usually diagnosed by skin biopsy. Each type of leiomyoma has unique histology.

How are leiomyomas treated?

Surgical excision is the definitive treatment for single lesions. Multiple cutaneous leiomyomas have a high rate of recurrence (~50%) within weeks to years – especially if part of HLRCC or Reed syndrome.

Medical treatment is not curative, but nifedipine, phenoxybenzamine and gabapentin may provide relief of pain.