혀에 발생한 증식성 근육염

Proliferative myositis is a rare, benign, probably pseudosarcomatous fibroblastic proliferation that typically presents as a rapidly growing soft tissue mass. Its relative rarity, fast growth rate, and unique histopathologic findings may lead to misdiagnosis as a malignant lesion and unnecessary radical surgical excision. A 57-year-old female presented with a non-tender, well-defined, indurated, solitary, hard papule on the median sulcus of the tongue for 2 weeks. Histologic examination revealed numerous fibroblastic or myofibroblastic spindle cells and large ganglion-like cells infiltrating between and around the muscle fascicles. Immunohistochemical staining showed positivity for vimentin, smooth muscle actin, and CD68 and negativity for S-100. Based on these characteristic clinical findings and histopathologic features, the patient was diagnosed with proliferative myositis. Here, we report a rare case of proliferative myositis on the tongue and recommend considering proliferative myositis in the differential diagnosis when a physician encounters a rapidly grown soft tissue mass. (Korean J Dermatol 2019;57(1):28∼31)