myositis (inflammatory myopathy)
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Classification
- primary or idiopathic
- dermatomyositis (acute or subacute onset)
- polymyositis (acute or subacute onset)
- inclusion body myositis (insideous onset)
- anti-synthetase syndrome (dyspnea, polyarthritis)
- secondary myositis (see etiology)
Etiology
- primary or idiopathic
- pharmacologic agents:
- gemfibrozil
- HMG CoA reductase inhibitors (statins)
- colchicine
- zidovudine (AZT)
- zalcitabine (ddC)
- cyclosporin A
- infectious agents
- generalized myositis
- localized myositis
- connective tissue disease
- malignancy
- trauma
Pathology
Clinical manifestations
- myalgias
- muscle pain or tenderness suggests infectious, thyroid or drug-induced myopathy[2]
- localized myositis/fasciitis (see fasciitis)
- generalized muscle weakness
- pyomyositis is a bacterial infection of muscle that usually results in abscess formation
- bacterial myositis is a more diffuse infection than pyomyositis that affects one or more muscle groups without abscess formation[3]
- some patients have relapsing-remitting disease
Laboratory
- serum chemistries
- elevated serum creatine kinase
- serum aldolase
- serum ALT & serum ALT may be elevated
- always check serum TSH when evaluating myopathy
- 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 (
- anti Jo1 antibodies
- myoglobinuria may be present
- eosinophilia may indicate trichinosis or cysticercosis
- 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]
- localized myositis/fasciitis (see fasciitis)
- see ARUP consult[7]
Diagnostic procedures
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
- pulmonary & cardiac complications in idiopathic myositis[2]
Management
- see specific myositis
- if myositis unresponsive to treatment, consider includion body myositis[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]
- screening for occult malignancy indicated in adults with newly diagnosed myositis & periodically thereafter[2]
- poor prognosis is associated with:
- profound muscle weakness at presentation
- older age at diagnosis
- associated malignancy
- delayed initiation of glucocorticoid therapy or refractory to glucocorticoids
- pulmonary disease
- some autoantibodies (anti-Jo1 Ab) & histologic patterns
More general terms
More specific terms
- anti-synthetase syndrome
- dermatomyositis
- diaphragmitis; acute primary diaphragmitis; Hedblom's syndrome
- inclusion body myositis (inflammatory myositis, IBM)
- polymyositis
Additional terms
References
- ↑ Harrison's Principles of Internal Medicine, 13th ed. Companion Handbook, Isselbacher et al (eds), McGraw-Hill Inc. NY, 1995, pg 829-39
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 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 - ↑ 3.0 3.1 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: https://www.ncbi.nlm.nih.gov/pubmed/16983604
- ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/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: https://www.ncbi.nlm.nih.gov/pubmed/17688836 - ↑ Targoff IN. Myositis specific autoantibodies. Curr Rheumatol Rep. 2006 Jun;8(3):196-203. PMID: https://www.ncbi.nlm.nih.gov/pubmed/16901077
- ↑ 6.0 6.1 Geriatric Review Syllabus, 7th edition Parada JT et al (eds) American Geriatrics Society, 2010
- ↑ 7.0 7.1 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 - ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/19439503
- ↑ Lundberg IE, Forbess CJ. Mortality in idiopathic inflammatory myopathies. Clin Exp Rheumatol. 2008 Sep-Oct;26(5 Suppl 51):S109-14. PMID: https://www.ncbi.nlm.nih.gov/pubmed/19026152
- ↑ Walker UA. Imaging tools for the clinical assessment of idiopathic inflammatory myositis. Curr Opin Rheumatol. 2008 Nov;20(6):656-61 PMID: https://www.ncbi.nlm.nih.gov/pubmed/18946324
- ↑ Amato AA, Griggs RC. Treatment of idiopathic inflammatory myopathies. Curr Opin Neurol. 2003 Oct;16(5):569-75. PMID: https://www.ncbi.nlm.nih.gov/pubmed/14501840
- ↑ 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: https://www.ncbi.nlm.nih.gov/pubmed/11412048
- ↑ Dimachkie MM, Barohn RJ. Idiopathic inflammatory myopathies. Semin Neurol. 2012 Jul;32(3):227-36 PMID: https://www.ncbi.nlm.nih.gov/pubmed/23117947
- ↑ Fasano S, Alves SC, Isenberg DA. Current pharmacological treatment of idiopathic inflammatory myopathies. Expert Rev Clin Pharmacol. 2016 Feb 6:1-12. PMID: https://www.ncbi.nlm.nih.gov/pubmed/26708717