Soft tissue

Fibroblastic / myofibroblastic

Focal myositis

Last author update: 1 July 2012
Last staff update: 30 March 2021

Copyright: 2002-2023,, Inc.

PubMed Search: Focal myositis [title]

Komal Arora, M.D.
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Page views in 2023 to date: 2,613
Cite this page: Arora K. Focal myositis. website. Accessed November 28th, 2023.
Definition / general
  • Inflammatory condition of skeletal muscle with degeneration and regeneration, inflammatory cells and fibrosis
  • Not a WHO diagnosis
  • Mean age 41 years, range 7 - 94 years
Clinical features
  • Usually healthy patients with no history of trauma
  • Evolves over weeks to a localized, painful soft tissue swelling, usually of lower extremity
  • Solitary, self limited, may be related to denervation
  • May be due to statins (Int J Cardiol 2009;133:e33, Cleve Clin J Med 2011;78:393)
Case reports
  • Usually none; spontaneously regresses
Gross description
  • Pale, ill defined
  • Mean 4 cm, range 1 - 20 cm
Microscopic (histologic) description
  • Degeneration and regeneration of muscle fibers associated with interstitial inflammation and fibrosis
  • Also focal neurogenic changes
  • Occasionally prominent eosinophils
  • Markedly inflamed cases have B cells or CD123+ dendritic plasma cells
Microscopic (histologic) images

Images hosted on other servers:

Focal perivascular
chronic inflammatory

Post BCG vaccination

Various images

Cytology description
  • Inflammatory cells, skeletal muscle fibers with degenerative and regenerative changes, fibrous tissue (Acta Cytol 2005;49:653)
Positive stains
Negative stains
Molecular / cytogenetics description
  • No B or T cell rearrangement
Differential diagnosis
  • Poliomyelitis
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