Soft tissue Tumors - Focal myositis

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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Focal myositis

Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 20 July 2012, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Inflammatory condition of skeletal muscle with degeneration and regeneration, inflammatory cells and fibrosis
● Not a WHO diagnosis

Epidemiology
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● Mean age 41 years, range 7-94 years

Clinical description
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● 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
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● 16 year old girl (J R Coll Surg Edinb 2000;45:339)
● 27 year old man post bCG vaccination (Rheumatology (Oxford) 2002;41:1074)
● 32 year old pregnant woman (Rheumatology (Oxford) 2000;39:211)
● 36 year old man with recurrent disease of peroneal muscles (Rheumatology (Oxford) 2002;41:1318)
● 43 year old man with Lyme disease (Arthritis Rheum 2006;54:2697)

Treatment
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● Usually none; spontaneously regresses

Gross description
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● Pale, ill-defined
● Mean 4 cm, range 1 to 20 cm

Micro description
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● 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
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Focal perivascular chronic inflammatory infiltrate

Post BCG vaccination

Various images

Cytology
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● Inflammatory cells, skeletal muscle fibers with degenerative and regenerative changes, fibrous tissue (Acta Cytol 2005;49:653)

Positive stains
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● CD163+ macrophages
● Lymphocytes are CD3+ and CD4+

Negative stains
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● Macrophages are S100- and CD1a-
● Lymphocytes are negative for TIA1, granzymeB, EBV and ALK1 (Am J Surg Pathol 2009;33:1016)

Molecular
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● No B or T cell rearrangement

Differential diagnosis
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● Poliomyelitis

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic tumors > Focal myositis

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