Benign nerve sheath myxoma (myxoid neurothekeoma) in the leg1. Institute of Pathology-ICMR, New Delhi, India. firstname.lastname@example.org 2. Department of Dermatology, Safdarjung Hospital,
New Delhi, India. 3. Institute of Pathology-ICMR, New Delhi , India
Singh Avninder MD1, V Ramesh MD2, Sarvjot Vermani MD3
Dermatology Online Journal 13 (2): 14
Myxoid neurothekeoma is a rare benign cutaneous neoplasm of nerve sheath origin and is also called as benign nerve sheath myxoma. This entity is seen in head, neck and upper extremity and seldom on the lower limb. A myxoid neurothekeoma in the lower leg of a 33-year-old woman is described.
Benign nerve sheath myxoma, also called as neurothekeoma (NT), is a rare cutaneous benign tumor of putative nerve sheath origin described in the head, neck, trunk and upper extremity. We describe a case of myxoid NT arising in the leg of a 33-year-old woman.
|A tender, solitary firm papule above the lateral malleolus of left leg|
A 33-year-old woman presented with a history of painful lesion on her lower leg of 3-years duration. The lesion was asymptomatic initially but had become painful since last 2 months. The pain was transient in nature and was precipitated by touch and pressure. Physical examination showed a solitary, raised, slightly erythematous papule of firm consistency measuring 6 mm in diameter on the posterior-lateral aspect of her left lower leg above the lateral malleolus [Fig. 1]. It was tender on palpation and showed no association with temperature or mobility of ankle joint. The lesion was excised completely and histopathological examination showed a multilobulated dermal lesion [Fig. 2] consisting of loosely arranged spindle and stellate cells within abundant stromal mucin [Fig. 3]. Immunohistochemistry showed these cells to be immunoreactive with S-100. After 1 year of follow up no recurrence was noted.
|Figure 2||Figure 3|
|Figure 2. Photomicrograph showing hypocellular tumor with multilobular pattern (H&E, x 40)|
|Figure 3. Photomicrograph showing spindle and stellate cells lying within stromal mucin (H &E, x 100)|
Myxoid NT or benign nerve sheath myxoma is a rare cutaneous neoplasm of putative peripheral nerve origin first described in 1969 by Harkin and Reed  and subsequently coined neurothekeoma by Gallager and Helwig  in 1980.
Neurothekeoma may be either asymptomatic or may present as a painful raised, skin colored, well-circumscribed dermal lesion averaging 1 cm in diameter. They are usually located in the head, neck and upper extremity of young females, and are rarely seen in the lower limb. Amongst the few cases reported in the lower limb, foot , hallux  and subungual location in the toe  have been described in literature. Another case reported in the ankle of a 62-year-old man showed extensive dystrophic calcification within the lobules of the tumor, which had prompted a misdiagnosis of foreign body granuloma . Clinically, a multitude of differential diagnoses exist for NT, including fibroma, dermatofibroma, leiomyoma, neurilemomma and neurofibroma.
The classic (myxoid) hypocellular variant as described above has a well-circumscribed, multilobulated growth pattern with loosely arranged spindle and stellate cells with S-100 positivity lying in copious stromal mucin and partitioned by collagen fibers. The cellular variant has an ill-defined fascicular growth pattern consisting of plump to epitheloid spindle cells, which may show nuclear atypia but lack stromal mucin and S-100 immunoreactivity. The third, mixed subtype shows features intermediate between classic and cellular types.
Despite the heterogeneity of immunohistochemical findings and variable interpretation of light microscopic features, there are currently three subtypes of NT recognized based on the tumor cellularity, growth pattern, amount of stromal mucin and S-100 positivity .
Although NT have in the past been reported as Pacinian neurofibroma, cutaneous lobular myxoma, myxomatous perineuroma, but recently, markers like protein gene product (PGP) 9.5 and NKI/ C3 and S100a6 have been proposed to be sensitive for identification of NT [8, 9, 10].
Although NT is rare in the lower extremity, the clinician should consider this entity in the differential diagnoses, as it is imperative to distinguish it from malignant lesions so that aggressive therapy could be avoided. The treatment of choice is excision with clear margins and no recurrences or metastasis have been reported.
References1. Harkin JC, Reed RJ. Tumors of the peripheral nervous system. In: Atlas of tumor pathology,AFIP,2nd ed,Washington DC,1969,p60.
2. Gallager RL, Helwig EB. Neurothekeoma: a benign cutaneous tumor of neural origin. Am J Clin Pathol 1980;74:759.
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8. Wang AR, May D, Bourne P, et al. PGP9.5: a marker for cellular neurothekeoma. Am J Surg Pathol 1999; 11:1401-1407.
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