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polymyositis

Inflammatory myopathy often grouped with dermatomyositis. Etiology: 1) autoimmune 2) associated with connective tissue disease 3) associated with malignancy Epidemiology: 1) adults < 50 years of age at onset* 2) male: female ratio 1:1, female > male [1] * distinguishing feature from dermatomyositis Pathology: 1) muscle biopsy a) myofibril necrosis b) cytotoxic T-cells (CD8+) * & macrophages infiltrating endomysial regions c) vessels of the muscle are spared* 2) serology, autoantibodies a) NO activation of complement* b) autoantibodies PMSCL1, PMSCL2 & Jo-1 * distinguishing features from dermatomyositis Genetics: - no familial association [1] Clinical manifestations: 1) no rash* 2) symmetric proximal muscle weakness a) onset is acute or subacute [1] 6) muscle pain (25%) 3) muscle weakness may involve the trunk & neck, but spares the face 4) pharyngeal & respiratory muscle weakness 5) dysphagia may develop from involvement of striated muscle of the pharynx 6) anti-synthetase syndrome occurs in some patients with polymyositis 7) hypoventilation secondary to proximal myopathy may be the most common cause of death * distinguishing feature from dermatomyositis Laboratory: 1) serum creatine kinase > 10-fold increase 2) muscle biopsy: a) gold-standard for diagnosis [1,4] b) inflammatory infiltrates* c) negative (normal) in 10-30% of affected patients 3) serology: (for classification, not diagnosis) [1] a) anti Jo-1 in serum (30%) - risk factor for interstitial lung disease b) antoantibodies against EXOSC9, EXOSC10, RUVBL1, PMSCL1, PMSCL2 c) antinuclear antibody in serum 4) always check serum TSH when evaluating myopathy * distinguishing feature from dermatomyositis Special laboratory: 1) electromyography: myopathic pattern 2) colonoscopy in elderly patients to evaluate for occult colorectal carcinoma [4] 3) pulmonary function testing [5] Radiology: - chest X-ray:evaluate for interstitial lung disease [1] - computed tomography - chest: evaluate for interstitial lung disease - thorax, abdomen, pelvis in elderly patients - evaluate for occult malignancy [4] - magnetic resonance imaging of muscle can identify sites for muscle biopsy, aid in the diagnosis & help assess response to treatment [1] - bone mineral density for patients treated long-term with glucocorticoids [1] Complications: - association with cancer not as strong as for dermatomyositis - modest increase in risk for some cancers [10] - lung disease may be most common cause of death - interstitial lung disease may precede muscle weakness [1] - hypoventilation secondary to proximal myopathy - other common causes of death - cancer, infections, cardiovascular events Differential diagnosis: 1) dermatomyositis 2) toxic myopathy - colchicine, zidovudine (AZT), statin, penicillamine, corticosteroids (steroid myopathy), alcohol 3) metabolic myopathy a) hypothyroidism: goiter, delayed reflexes, myalgias, weight gain b) mitochondrial myopathy c) glycogen storage disease 4) myasthenia gravis: oculomotor muscle weakness, ptosis 5) HIV 6) polymyalgia rheumatica: proximal muscle tenderness 7) vasculitis 8) eosinophilia myalgia syndrome 10) muscular dystrophies 11) inclusion body myositis 12) carnitine deficiency 13) adenylate deaminase deficiency 14) amyotrophic lateral sclerosis (ALS): muscle fasciculations 15) myasthenia gravis 16) polymalgia rheumatica 17) peripheral neuropathy: muscle atrophy, hyporeflexia 18) mixed connective tissue disease Management: 1) combination of prednisone + other immunosuppressive agent 2) response to glucocorticoids is variable* 3) patients may respond to methotrexate or other immunosuppressive agent 4) physical therapy to maintain muscle strength 5) supportive therapy - calcium & vitamin D for patients treated long-term with glucocorticoids [1]

Interactions

disease interactions

Related

dermatomyositis

General

autoimmune disease myositis (inflammatory myopathy)

References

  1. Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 1998, 2006, 2009, 2012, 2015, 2018, 2022. - Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022
  2. Fathi M, Lundberg IE, Tornling G. Pulmonary complications of polymyositis and dermatomyositis. Semin Respir Crit Care Med. 2007 Aug;28(4):451-8. PMID: 17764062
  3. Ytterberg SR. Treatment of refractory polymyositis and dermatomyositis. Curr Rheumatol Rep. 2006 Jun;8(3):167-73. PMID: 16901073
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  6. 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
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  8. Selva-O'Callaghan A, Grau JM, Gamez-Cenzano C, Conventional cancer screening versus PET/CT in dermatomyositis/ polymyositis. Am J Med. 2010 Jun;123(6):558-62. PMID: 20569766
  9. Walker UA. Imaging tools for the clinical assessment of idiopathic inflammatory myositis. Curr Opin Rheumatol. 2008 Nov;20(6):656-61 PMID: 18946324
  10. Hill CL, Zhang Y, Sigurgeirsson B et al Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study. Lancet. 2001 Jan 13;357(9250):96-100. PMID: 11197446
  11. Airio A , Kautiainen H, Hakala M. Prognosis and mortality of polymyositis and dermatomyositis patients. Clin Rheumatol. 2006 Mar;25(2):234-9. Epub 2006 Feb 14 PMID: 16477398
  12. Bernatsky S, Joseph L, Pineau CA et al Estimating the prevalence of polymyositis and dermatomyositis from administrative data: age, sex and regional differences. Ann Rheum Dis. 2009 Jul;68(7):1192-6 PMID: 18713785
  13. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet. 2003 Sep 20;362(9388):971-82. PMID: 14511932
  14. Marie I, Hachulla E, Hatron PY et al Polymyositis and dermatomyositis: short term and longterm outcome, and predictive factors of prognosis. J Rheumatol. 2001 Oct;28(10):2230-7. PMID: 11669162
  15. National Institute of Neurological Disorders and Stroke (NINDS) NINDS Polymyositis Information Page https://www.ninds.nih.gov/Disorders/All-Disorders/Polymyositis-Information-Page