[Clinicopathologic features of dermal nerve sheath myxoma and neurothekeoma: a comparative study]

Objective: To investigate the clinicopathologic characteristics and differential diagnosis of dermal nerve sheath myxoma (DNSM) and neurothekeoma (NTK). Methods: Clinical, pathological features and immunohistochemical profiles in 9 cases of DNSM and 8 cases of NTK were comparatively studied. The literature was reviewed. Results: The involved site of 9 DNSMs included the hand/fingers (n=3), ear (n=2), face, back, abdominal wall and waist (1 case each). Two of 8 NTKs arose in the forearm (n=2), one each in the nose, lip, shoulder, supraclavicular region, leg and hand. The most common presentation was a painless cutaneous nodule or plaque which grew slowly. Grossly, DNSM was often gelatinous, whereas NTK appeared relatively solid. Microscopically, both tumors were located in the dermis and/or subcutis. DNSM was composed of well-defined multiple lobules separated by fibrous septa. NTK also exhibited lobular or multinodular architecture, but was relatively ill-defined. Besides, fascicular or whorl-like arrangement was present in 3 cases of NTK. The lobules in DNSM consisted of a paucicellular proliferation of spindled, stellate and epithelioid cells forming interconnecting cords within abundant myxoid matrix. Small syncytial-like aggregates were readily noted. The constituted neoplastic cells in NTK were composed of ovoid to round epithelioid or histiocytoid cells. Scattered multinucleated giant cells were present in 2 cases. Based on the amount of myxoid matrix, 8 NTKs were further classified into cellular (5 cases), mixed (2 cases) and myxoid (1 case). By immunohistochemistry, neoplastic cells in DNSM were diffusely positive for S-100 protein, CD68, glial fibrillary acidic protein and SOX10, whereas neoplastic cells in NTK consistently expressed CD10 and microphthalmia transcription factor, with negativity for S-100 protein and SOX10. One patient each with DNSM and NTK experienced local recurrence due to incomplete excision. Conclusions: Although DNSM and NTK share clinical and pathological features, they belong to different entities. Whereas the former is consistent with a peripheral nerve sheath tumor, the latter is more akin to fibrous histiocytic tumor. Familiarity with their cliniopathologic characteristics and distinctive immunophenotypes will help distinguishing these two entities, as well as in the differential diagnosis of cutaneous neoplasms with similar features.