A Case of Proliferative Myositis Arising from the Sternocleidomastoid Muscles: Diagnosis and Treatment

We describe here diagnosis treatment of a case that rose from the sternocleidomastoid muscle and was treated without surgical excision. A 56-year-old man presented with a rapidly growing, painless and not well-circumscribed mass at the right side of the neck. We diagnosed this tumor as proliferative myositis (PM) based on the typical findings from ultrasonography, computed tomography, and core-needle biopsy, and treated it without surgical excision. Herein we report a successful diagnosis and treatment process of a case of PM, which was followed-up with ultrasonography.

Proliferative Myositis: A Comprehensive Review of 33 Case Reports

Proliferative myositis, a rare reactive intramuscular myofibroblastic proliferation, is not well recognized in clinical practice. It overgrows within a few weeks and expands the space between the muscle causing infiltrative-like border mimicking sarcoma. Knowledge of the natural history and pathology of proliferative myositis is essential in order to prevent misdiagnosis and unnecessary surgical resection. Thirty-three reported cases of proliferative myositis in PubMed and Web of Science databases from 2000 to 2018 had been reviewed with the main emphasis in clinical presentation, radiological and pathological findings, treatment, and prognosis. Both males (19 cases) and females (14 cases), predominantly the middle-aged and senior adults, were affected. Upper extremity and shoulder girdle were commonly involved. The chief complaint varied from either painful or painless mass. The traumatic injury was reported as a significant predisposing factor. The lesion typically proliferated and separated muscle bundle. Ultrasonography of the lesion revealed a characteristic “checkerboard pattern” on transverse view. The definite diagnosis was based on the demonstration of spindle-shaped fibroblast/myofibroblast admixed with giant ganglion-like cells in the biopsy. Immunohistochemistry may be useful diagnostic tool when the histopathology was inconclusive. Misdiagnosis of sarcoma occurred due to its rapid growth and infiltrative-like border. Watchful management without surgery was sufficient because of the potential for spontaneous regression. Thoroughly clinical examination and appropriate investigations, including imaging and histopathology, are crucial.