Focal myositis: a literature review of clinical and immunopathological aspects.

Objectives: Focal myositis (FM) is a rare and restricted skeletal muscle inflammation, presenting as a solid mass with a typical lower leg localization and benign prognosis. In most cases the process solves spontaneously or after immunosuppressant therapy, but sometimes it recurs or progresses to a systemic inflammation. The basis of the disease are mostly unknown.

Methods: Hence, we provide an update of histopathological features of FM, in order to better define the underlying pathomechanisms of this disorder. A PubMed literature search was focused on the case reports published in English from July 1977 to December 2023.

Results: FM and other myositis may show similar morphological features. Emerging studies on MMP molecules and future eventual research on microRNAs (miRNAs) could help in differential diagnosis.

Conclusions: Clinical, laboratory, neurophysiological and imaging findings can allow a correct diagnosis. However, muscle biopsy seems to be the only diagnostic tool to differentiate among FM and other localized soft tissue masses.