Proliferative Myositis: A Comprehensive Review of 33 Case Reports

Abstract

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.

Sarcomatoid Lesions of Head and Neck Region: A Diagnostic Dilemma

“…The lesion is typically composed of spindle cells arranged in parallel or herringbone pattern, without ganglion-like cells. Spindle cells in adult-type fibrosarcoma are more cellular than that of proliferative myositis [8].…”

“…Giant ganglion-like cells in proliferative myositis may mimic and be mistaken for sarcomas, most commonly rhabdomyosarcoma or ganglio-neuroblastoma. In proliferative myositis ganglionlike cells lack cross-striations and show more cytoplasmic basophilia than that of rhabdomyoblasts [8].…”

“…Spindle cell lesions with overlapping histologic features with PM include nodular fasciitis, desmoid fibromatosis, or adult-type fibrosarcoma. Giant/bizarre ganglion-like cells may be sometimes confused with rhabdomyoblasts in rhabdomyosarcoma, or ganglion cells and neuroblasts in ganglioneuroblastoma [8].…”

“…Desmoid fibromatosis is a poorly demarcated tumor composed of spindle-shaped myofibroblasts arranged in sweeping fascicles without giant ganglion-like cells. So it can be differentiated on that basis histologically [8].…”

“…Ganglioneuroblastoma comprises of fascicles of Schwann cells with variable numbers of ganglion cells, resembling proliferative myositis in a limited biopsy. Immunohistochemistry is very helpful to distinguish these entities [8].…”