Home > E. Pathology by systems > Locomotory system > Muscles > focal myositis
focal myositis
Tuesday 5 May 2009
Digital cases
Definition: Focal myositis is an uncommon inflammatory pseudotumor of skeletal muscle that can be confused with a variety of neoplastic and inflammatory diseases.
It is often misunderstood because it presents as a tumor-like mass, but histologically resembles a skeletal muscle myopathy or dystrophy.
Focal myositis occurs in specific muscle groups of young adults of both sexes without significant trauma.
It is a largely unrecognized entity with specific histology including myopathic, focal neurogenic, fibrosis, and inflammatory features.
It can be easily mistaken for an inflammatory myopathy, dystrophy, alternate reactive, or even neoplastic process.
Focal myositis seems to be a macrophage and T-cell-rich lesion that changes to B cell and dendritic plasmacytoid cells when markedly inflamed, but does not seem to have a known viral or molecular etiology.
IgG4 presence may be linked to the fibrosis in these lesions; a possible transient autoimmune etiology cannot be excluded.
See also
myositis ossificans
References
Focal Myositis: A Clinicopathologic Study of 115 Cases of an Intramuscular Mass-like Reactive Process. Auerbach A, Fanburg-Smith JC, Wang G, Rushing EJ. Am J Surg Pathol. 2009 Apr 9. PMID: 19363438