Soft tissue
Fibroblastic / myofibroblastic tumors
Focal myositis

Author: Komal Arora, M.D. (see Authors page)

Revised: 18 August 2016, last major update July 2012

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Focal myositis [title]

Definition / General
  • Inflammatory condition of skeletal muscle with degeneration and regeneration, inflammatory cells and fibrosis
  • Not a WHO diagnosis
Epidemiology
  • 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
Treatment
  • Usually none; spontaneously regresses
Gross Description
  • Pale, ill-defined
  • Mean 4 cm, range 1 - 20 cm
Micro 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
Micro Images

Images hosted on other servers:

Focal perivascular chronic inflammatory infiltrate

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