Atypical leiomyoma: An unusual variant of cutaneous pilar leiomyoma
Dermatology Department, Hospital Churruca, Buenos Aires, Argentina. firstname.lastname@example.org
Cutaneous atypical leiomyoma is an unusual benign tumor arising from arrector pili muscle that shares histological features with uterine atypical or symplastic leiomyoma: atypical cellularity with pleomorphic nuclei but minimal or no mitosis. Six other cases have been reported so far and, in spite of its name and of being a smooth muscle proliferation, no recurrences nor metastasis have been reported.
Cutaneous leiomyoma is a rare, benign, smooth muscle tumor. It has been divided into different subtypes according to the skin structures from which it can derive:
1. Cutaneous pilar leiomyoma, arising from arrector pili muscle;
Cutaneous pilar leiomyoma usually presents as multiple tumors and, though sporadic in the vast majority, a familial autosomic dominant pattern of inheritance has been described. A similar pattern of inheritance has been reported in some women with early uterine leiomyomatosis and cutaneous leiomyomas. This condition is known as Reed syndrome or multiple leiomyomatosis [2, 3]. Presentation of the lesion as a solitary tumor is less common.
There have been some previous reports of cutaneous pilar leiomyomas with atypical cellularity, similar to the findings in symplastic uterine leiomyomas. We hereby present the case of a female patient with an atypical leiomyoma.
68-year-old female patient with a history of hypertension presented with a reddish asymptomatic nodule measuring 1 cm in diameter located in her right thigh of 2 years of evolution (Fig. 1).
Cutaneous biopsy revealed a dermal fusocellular proliferation with pleomorphic and atypical nuclei. There was no evidence of mitosis (Fig. 2 and 3). Stains for actin and desmin were positive whereas S100 and Ki67 were negative (Fig. 4 and 5). The diagnosis of atypical leiomyoma was made. The lesion was surgically removed with free margins, No recurrences were seen in a 6 month follow-up period.
Cutaneous pilar leiomyomas are benign smooth muscle tumors that appear between the second and third decades of life as multiple, painful red-brown papulonodules. They are located on the face, back and extensor aspect of extremities. A germline gene mutation responsible for the multiple familial form of these tumors has been identified in the gene that encodes a tumor suppressor enzyme, fumarate hydratase; this has been located in chromosome 1q42.3-43 . It must be remembered that this syndrome also includes uterine fibroids and may be associated with renal cell carcinoma [4, 5].
Solitary cutaneous pilar leiomyomas, on the other hand, are usually asymptomatic and larger in size than those encountered in patients with the multiple form.
Leiomyosarcomas account for the malignant variant of the lesion. They can originate from dermis and subcutaneous tissue as solitary tumors located in the extremities. When superficial, metastases after surgical removal are very rare but local recurrences are found in 40 percent. Mohs's micrographic surgery is therefore the treatment of choice .
Atypical leiomyoma or symplastic leiomyoma is an unusual variant of cutaneous pilar leiomyoma; only 6 cases are reported in the literature so far. It shares histological features with symplastic leiomyoma of the uterus: atypic cellularity, pleomorphic nuclei, and minimal or no mitosis .
This tumor presents as painful or asymptomatic solitary red-brown nodules and the predominant location is on the extremities. It has been more frequently observed in men. The differential diagnosis includes other benign tumors such as schwannomas, fibrohystiocytomas, and neuromas.
Histologically, leiomyoma is a non-encapsulated dermal proliferation composed of myocytes with an abundant eosinophylic cytoplasm without atypical cells or mitoses, whereas leiomyosarcoma is a highly pleomorphic proliferation of atypical myocytes and a significant number of mitoses. A recent review of leiomyosarcomas demonstrated the presence of 9 or more mitoses per 10 high power field in the 84 percent of the tumors .
This finding is crucial to distinguish benign leiomyomas from leiomyosarcomas. Atypical cutaneous leiomyoma stands in the middle of the cutaneous leiomyoma spectrum exhibiting atypical myocytes and giant cells but with minimal or absent mitoses.
The tumor stains positive for smooth muscle actin and desmin and negative for S100 and Ki67, which is a histological marker for mitoses. Based on the experience with uterine symplastic leiomyomas (a review of cases with a ten-year follow-up period found no recurrences nor metastasis), surgical excision of the tumor with free margins is the proposed treatment of choice for the cutaneous atypical leiomyoma.
Despite a short follow up period of no more than two years, none of the six cutaneous atypical leiomyomas previously reported recurred or metastasized. Nevertheless, a close follow up of the patients is recommended, especially if two or more mitoses per ten high power fields are present.
References1. Sherwani RK, Rahman K, Akhtar K, Zaheer S et al. Leiomyoma of scrotum. Indian J Pathol Microbiol.2008; 51:72-3. [PubMed]
2. Weedon. Tumores del músculo liso, cartílago y hueso en Piel. In Patología. Weedon D, Strutton G, 1era Edic. Marbán, MADRID.2002, 795-6.
3. Alam Na, Barclay E, Rowan AJ, Tyrer JP et al. Clinical features of multiple cutaneous and uterine leiomyomatosis, an underdiagnosed tumor syndrome. Arch Dermatol.2005; 141:199-206. [PubMed]
4. Ghaninejad H, Moeineddin F, Rajaee A, Asgari M, Salimzadeh A. Hereditary leiomyomatosis and renal cell carcinoma syndrome: a case report. Dermatol Online J. 2008; 14(1):16. [PubMed]
5. Stewart L, Glenn GM, Stratton P, Goldstein AM, Merino MJ, Tucker MA, Linehan WM, Toto JR. Association of germline mutations in the fumarate hydratase gene and uterine fibroids in women with hereditary leiomyomatosis and renal cell cancer. Arch Dermatol. 2008 Dec 144 (12): 1584-92. [PubMed]
6. Matthews JH, Pichardo RO, Hichtcock MG, Lesshin B. Cutaneous leiomyoma with cytologic atypia-akin to uterine symplastic leiomyoma. Dermatol Surg.2004; 30:1249-51. [PubMed]
7. Usmani N, Merchant W, Yung A. A case of cutaneous symplastic leiomyoma-a rare variant of cutaneous pilar leiomyoma. J Cutan Pathol.2008; 35:229-31. [PubMed]
8. Kaddu S, Beham A, Cerroni L et al. Cutaneous leiomyosarcoma. Am J Surg Pathol.1997; 21: 979-87. [PubMed]
© 2009 Dermatology Online Journal