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myositis (inflammatory myopathy)

Classification: 1) primary or idiopathic a) dermatomyositis b) polymyositis c) inclusion body myositis d) anti-synthetase syndrome 2) secondary myositis (see etiology) Etiology: 1) primary or idiopathic 2) pharmacologic agents: a) gemfibrozil b) HMG CoA reductase inhibitors (statins) - lovastatin - simvistatin - atorvastatin c) colchicine d) zidovudine (AZT) e) zalcitabine (ddC) f) cyclosporin A 3) infectious agents a) generalized myositis - enterovirus - coxsackievirus - influenza - Epstein Barr virus (EBV) - Legionella - trichinosis - cysticercosis - toxoplasmosis - Lyme disease - HIV infection b) localized myositis - Clostridium perfringens - group A streptococcus - mixed anaerobic & aerobic organisms (trauma) - Staphylococcus aureus - gram negative rods in diabetics - Bacillus cereus - Vibrio vulnificus 4) connective tissue disease 5) malignancy 6) trauma Pathology: - inflammation of skeletal muscle Clinical manifestations: 1) myalgias - muscle pain or tenderness suggests infectious, thyroid or drug-induced myopathy [2] 2) localized myositis/fasciitis (see fasciitis) 3) generalized muscle weakness - proximal muscle weakness > distal muscle weakness 4) pyomyositis is a bacterial infection of muscle that usually results in abscess formation 5) bacterial myositis is a more diffuse infection than pyomyositis that affects one or more muscle groups without abscess formation [3] 6) some patients have relapsing-remitting disease Laboratory: 1) serum chemistries a) elevated serum creatine kinase b) serum aldolase c) serum ALT & serum ALT may be elevated d) always check serum TSH when evaluating myopathy 2) serology - anti Jo1 antibodies - highly specific for primary inflammatory myositis [2] - associated with risk of interstitial lung disease & death - HMG CoA reductase Ab in serum ( - immune-mediated necrotizing myopathy [2] 3) myoglobinuria may be present 4) eosinophilia may indicate trichinosis or cysticercosis 5) open muscle biopsy is gold standard - obtain biopsy from contralateral site of that studied by electromyography [2] - percutaneous needle biopsy does not permit accurate assessment of muscle morphology [6] 6) localized myositis/fasciitis (see fasciitis) 7) see ARUP consult [7] Special laboratory: - electromyography - nerve conduction studies Radiology: - localized myositis/fasciitis (see fasciitis) - magnetic resonance imaging - assess degree of muscle inflammation - identify promising biopsy site - bone mineral density for patients treated long-term with glucocorticoids [2] Complications: - malignancy associated with myositis typically occur in older patients & more often develops in patients with dermatomyositis - ovarian cancer, lung cancer, pancreatic cancer, gastric cancer, colon cancer, lymphoma - pulmonary & cardiac complications in idiopathic myositis [2] Management: 1) see specific myositis - if myositis unresponsive to treatment, consider includion body myositis [2] 2) idiopathic myositis is generally treated with glucocorticoids with addition of DMARD (methotrexate, azathioprine) - calcium & vitamin D for patients treated long-term with glucocorticoids [2] 3) screening for occult malignancy indicated in adults with newly diagnosed myositis & periodically thereafter [2] 4) poor prognosis is associated with: a) profound muscle weakness at presentation b) older age at diagnosis c) associated malignancy d) delayed initiation of glucocorticoid therapy or refractory to glucocorticoids e) pulmonary disease f) some autoantibodies (anti-Jo1 Ab) & histologic patterns

Interactions

disease interactions

Related

fasciitis

Specific

anti-synthetase syndrome dermatomyositis diaphragmitis; acute primary diaphragmitis; Hedblom's syndrome inclusion body myositis (inflammatory myositis, IBM) polymyositis

General

inflammation muscular disease; myopathy

References

  1. Harrison's Principles of Internal Medicine, 13th ed. Companion Handbook, Isselbacher et al (eds), McGraw-Hill Inc. NY, 1995, pg 829-39
  2. Medical Knowledge Self Assessment Program (MKSAP) 11,15,17,18,19. American College of Physicians, Philadelphia 1998,2009,2015,2018,2022. - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  3. Pannaraj PS et al, Infective pyomyositis and myositis in children in the era of community-acquired, methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis 2006, 49:953 PMID: 16983604
  4. Hengstman GJ, van den Hoogen FH, van Engelen BG. Treatment of the inflammatory myopathies: update and practical recommendations. Expert Opin Pharmacother. 2009 May;10(7):1183-90. Review. PMID: 19405792 - Hengstman GJ Advances in the immunopathophysiology of the idiopathic inflammatory myopathies: not as simple as suspected. Curr Rheumatol Rep. 2007 Aug;9(4):280-5. PMID: 17688836
  5. Targoff IN. Myositis specific autoantibodies. Curr Rheumatol Rep. 2006 Jun;8(3):196-203. PMID: 16901077
  6. Geriatric Review Syllabus, 7th edition Parada JT et al (eds) American Geriatrics Society, 2010
  7. ARUP Consult: Inflammatory Myopathies The Physician's Guide to Laboratory Test Selection & Interpretation https://www.arupconsult.com/content/inflammatory-myopathies - ARUP Consult: Idiopathic Inflammatory Myopathies (Myositis) https://arupconsult.com/ati/idiopathic-inflammatory-myopathies
  8. Gunawardena H, Betteridge ZE, McHugh NJ. Myositis-specific autoantibodies: their clinical and pathogenic significance in disease expression. Rheumatology (Oxford). 2009 Jun;48(6):607-12 PMID: 19439503
  9. Lundberg IE, Forbess CJ. Mortality in idiopathic inflammatory myopathies. Clin Exp Rheumatol. 2008 Sep-Oct;26(5 Suppl 51):S109-14. PMID: 19026152
  10. Walker UA. Imaging tools for the clinical assessment of idiopathic inflammatory myositis. Curr Opin Rheumatol. 2008 Nov;20(6):656-61 PMID: 18946324
  11. Amato AA, Griggs RC. Treatment of idiopathic inflammatory myopathies. Curr Opin Neurol. 2003 Oct;16(5):569-75. PMID: 14501840
  12. Buchbinder R, Forbes A, Hall S, Dennett X, Giles G. Incidence of malignant disease in biopsy-proven inflammatory myopathy. A population-based cohort study. Ann Intern Med. 2001 Jun 19;134(12):1087-95. PMID: 11412048
  13. Dimachkie MM, Barohn RJ. Idiopathic inflammatory myopathies. Semin Neurol. 2012 Jul;32(3):227-36 PMID: 23117947
  14. Fasano S, Alves SC, Isenberg DA. Current pharmacological treatment of idiopathic inflammatory myopathies. Expert Rev Clin Pharmacol. 2016 Feb 6:1-12. PMID: 26708717