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Polymyositis

Original Editors - Chris Pyles & Kayla Thiesen from Bellarmine University's Pathophysiology of Complex Patient Problems project.

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Definition/Description 

Polymyositis (PM) is a rare, chronic autoimmune idiopathic inflammatory myopathy (IIM) characterised by progressive, symmetric proximal muscle weakness and inflammatory infiltration of skeletal muscle tissue. It falls within the broader category of IIMs (heteogenous disorders collectively referred to as myositis) alongside dermatomyositis(DM), immune-mediated necrotising myopathy (IMNM), inclusion body myositis (IBM) and anti-synthetase syndrome(ASS).[1][2]

[3]

Epidemiology

Polymyositis is a rare condition with a prevalence of approximately 1 per 100,000 in the general population, appearing twice as often in women as it does in men. While the disease is rarely seen in individuals under the age of 18, it typically reaches its incidence in adults between the ages of 40 and 60 [4][5]

Clinical Presentation

The predominant symptom is proximal muscle weakness which is symmetrical and can gradually appear or may fluctuate within short or long periods of time.[6][7] Functionally, patients may have issues with grabbing a glass off of a high shelf, climbing stairs, or getting up or sitting down on a couch. With progression of the disease, neck and shoulder girdle musculature can be involved resulting in minimal muscle contraction or paralysis.[7]
General signs and symptoms are:

  • Proximal muscle weakness[8] [6]
  • Difficult swallowing (dysphagia)
  • Difficulty swallowing (dysphasia)
  • Difficulty speaking
  • Arthralgia[6][7]
  • Fatigue
  • Shortness of breath[6]

As PM progresses, it can affect the upper oesophagus as well as striated muscle fibres in the chest wall. As a result, patients can have more complex signs and symptoms such as:

  • Aspiration pneumonia
  • Respiratory failure[9]
  • Variety of cardiovascular complications (i.e. CHF, arrhythmias)[7]
  • Interstitial lung disease[9]


Associated Co-morbidities

Since Polymyositis is a an autoimmune disease, it is often associated with other autoimmune diseases and infectious disorders:

Diagnostic Tests

There are several different diagnostic tools to determine if a patient has polymyositis, it can be a long process and both health care providers as well as patients are encouraged to remain patient:

  • Magnetic Resonance imaging (MRI)
  • Electromyography[3]
  • Muscle Biopsy (looking for inflammation, damage, or infection/abnormal proteins and enzyme deficiencies)[6][7][3]
  • Blood Tests:[7]
    1. Increased Creatine Kinase
    2. Increased Aldolase

Medical Management

Treatment follows a stepwise approach based on disease severity and response.

First-Line: Glucocorticoids[11]

Oral prednisolone (0.5–1 mg/kg/day) is the cornerstone of initial treatment. Glucocorticoids remain the mainstay of treatment, though many patients require additional immunosuppressive agents due to insufficient response, relapse during tapering, or significant side effects.

Second-Line: Steroid-Sparing Agents [12]

Early combination is recommended to facilitate steroid tapering:

  • Methotrexate (10–25 mg/week) — preferred first add-on
  • Azathioprine (1–3 mg/kg/day) — alternative, especially with lung involvement
  • Mycophenolate mofetil (1.5–3 g/day) — preferred in PM-associated ILD
  • Tacrolimus — particularly effective in ILD; demonstrated benefit on disease-free and event-free survival in PM/DM-associated ILD.
Third-Line: Refractory Disease[13]

Rituximab: anti-CD20 biologic; 83% of refractory myositis patients met improvement criteria in the RIM trial

Physical Therapy Management

Polymyositis and other idiopathic inflammatory myopathies present with wide ranging systemic clinical manifestations. The hallmark clinical feature of polymyositis is progressive, symmetric proximal muscle weakness that develops over weeks or months, with the symmetrical weakness being more pronounced in the proximal muscle groups like the neck, shoulders, upper chest, back, arms and lateral thighs.[14] Patients with systemic spread can complain of breathing difficulty or chest tightness due to infiltrative cardiomyopathy or pericarditis, and polymyositis can cause interstitial lung disease.[15][16] Exercise is a safe and effective treatment to optimise health and reduce disability, and exercise could now be considered as medicine.[17]

Aerobic Exercise (Cardiovascular/Endurance Training):

Aerobic exercise and resistance training at moderate-to-high intensity can improve aerobic capacity, muscle impairment, activity limitation, quality of life, and disease activity (limited evidence) in patients with established polymyositis and dermatomyositis.[18] A six-week training programme including bicycle exercise and step aerobics produced significant improvement in ADL performance, muscle strength, and VO₂ max in the exercise group. [19]

Resistance Training:

Sixteen weeks of high-intensity resistance training can improve quality of life, muscle endurance, and strength in patients with stable polymyositis compared to usual care. [20]

Differential Diagnosis

Given the intense treatment regimen that is association with autoimmune disorders it is very important that clinicians make an accurate diagnosis in the cases of inflammatory myopathies. Muscle biopsy is essential for an accurate diagnosis, however it is recognised that there is a pathological overlap in different inflammatory myopathies (ex: polymyositis and dermatomyositis) and other muscle disorders such as congenital muscular dystrophies.[7]

Resources

References

  1. ↑ Dourado E, Bottazzi F, Cardelli C, Conticini E, Schmidt J, Cavagna L, Barsotti S. Idiopathic inflammatory myopathies: one year in review 2022. Clin Exp Rheumatol. 2023 Mar;41(2):199-213.https://pubmed.ncbi.nlm.nih.gov/36826800/
  2. ↑ Hunter K, Lyon MG. Evaluation and management of polymyositis. Indian Journal of Dermatology. 2012 Sep 1;57(5):371-4.https://pmc.ncbi.nlm.nih.gov/articles/PMC3482800/
  3. ↑ 3.0 3.1 3.2 Johns Hopkins Rheumatology. Polymyositis Overview : Johns Hopkins Myositis Center. Available from: http://www.youtube.com/watch?v=aYeH5Y0ozxw [last accessed 30/1/2023]
  4. ↑ Carstens PO, Schmidt J. Diagnosis, pathogenesis and treatment of myositis: recent advances. Clinical & Experimental Immunology. 2014 Mar;175(3):349-58.https://pmc.ncbi.nlm.nih.gov/articles/PMC3927896/#b1
  5. ↑ Bronner IM, Van Der Meulen MF, De Visser M, Kalmijn S, Van Venrooij WJ, Voskuyl AE, Dinant HJ, Linssen WH, Wokke JH, Hoogendijk JE. Long-term outcome in polymyositis and dermatomyositis. Annals of the rheumatic diseases. 2006 Nov 1;65(11):1456-61.https://pmc.ncbi.nlm.nih.gov/articles/PMC1798355/#:~:text=Dermatomyositis%20and%20polymyositis%20are%20serious,despite%20the%20regained%20muscle%20strength.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Hunter K, Lyon MG. Evaluation and management of polymyositis. Indian Journal of Dermatology. 2012 Sep 1;57(5):371.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Carstens PO, Schmidt J. Diagnosis, pathogenesis and treatment of myositis: recent advances. Clinical & Experimental Immunology. 2014 Mar;175(3):349-58.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Schmidt J. Current classification and management of inflammatory myopathies. Journal of neuromuscular diseases. 2018 Jan 1;5(2):109-29.
  9. ↑ 9.0 9.1 9.2 Fujisawa T. Management of myositis-associated interstitial lung disease. Medicina. 2021 Apr 3;57(4):347.
  10. ↑ Sharif K, Ben-Shabat N, Mahagna M, Shani U, Watad A, Cohen AD, Amital H. Inflammatory Bowel Diseases Are Associated with Polymyositis and Dermatomyositis—A Retrospective Cohort Analysis. Medicina. 2022 Nov 25;58(12):1727.
  11. ↑ Pipitone N, Salvarani C. Up-to-date treatment and management of myositis. Current Opinion in Rheumatology. 2020 Nov 1;32(6):523-7. https://pubmed.ncbi.nlm.nih.gov/32890030/
  12. ↑ Kurita T, Yasuda S, Amengual O, Atsumi T. The efficacy of calcineurin inhibitors for the treatment of interstitial lung disease associated with polymyositis/dermatomyositis. Lupus. 2015 Jan;24(1):3-9.https://pubmed.ncbi.nlm.nih.gov/25297551/
  13. ↑ Moghadam-Kia S, Oddis CV. Current and new targets for treating myositis. Current Opinion in Pharmacology. 2022 Aug 1;65:102257.https://www.sciencedirect.com/science/article/abs/pii/S1471489222000844
  14. ↑ Harris-Love MO, Shrader JA, Koziol D, Pahlajani N, Jain M, Smith M, Cintas HL, McGarvey CL, James-Newton L, Pokrovnichka A, Moini B. Distribution and severity of weakness among patients with polymyositis, dermatomyositis and juvenile dermatomyositis. Rheumatology. 2009 Feb 1;48(2):134-9.https://pubmed.ncbi.nlm.nih.gov/19074186/
  15. ↑ Kannappan R, Kumar R, Cichelli K, Brent LH. A review of myositis-associated interstitial lung disease. Journal of Clinical Medicine. 2024 Jan;13(14):4055.https://pmc.ncbi.nlm.nih.gov/articles/PMC11278012/?fbclid=IwY2xjawQj9bFleHRuA2FlbQIxMABicmlkETFLNTNrYWc4VXVQRjdybkMxc3J0YwZhcHBfaWQQMjIyMDM5MTc4ODIwMDg5MgABHl0kGpOfmqqlZov5qVm0Jsb31WvqyrhIzXZGHD1qGHLbhuBNF46Fsa41VP5X_aem_9Pw-kKX5dIofOn1_5GlmlQ
  16. ↑ Sehgal S, Patel A, Chatterjee S, Fernandez AP, Farver C, Yadav R, Li Y, Danoff SK, Saygin D, Huapaya JA, Wilfong EM. Idiopathic inflammatory myopathies related lung disease in adults. The Lancet Respiratory Medicine. 2025 Mar 1;13(3):272-88.https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(24)00267-4/abstract
  17. ↑ Kannappan R, Kumar R, Cichelli K, Brent LH. A review of myositis-associated interstitial lung disease. Journal of Clinical Medicine. 2024 Jan;13(14):4055. https://www.mdpi.com/2077-0383/13/14/4055
  18. ↑ Andreasson KM, Leijding C, Dastmalchi M, Notarnicola A, Gastaldello S, Yamada T, Sandlund H, Leonard D, Westerblad H, Lundberg IE, Andersson DC. High-intensity interval training outperforms moderate exercise to improve aerobic capacity in patients with recent-onset idiopathic inflammatory myopathies: a multicentre randomised controlled trial. Ebiomedicine. 2025 Dec 1;122.[1]
  19. ↑ Sarwar A, Dydyk AM, Jatwani S. Polymyositis. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK563129/
  20. ↑ Zhang L, Wu G, Gao D, Liu G, Pan L, Ni L, Li Z, Wang Q. Factors associated with interstitial lung disease in patients with polymyositis and dermatomyositis: a systematic review and meta-analysis. PloS one. 2016 May 12;11(5):e0155381.https://pmc.ncbi.nlm.nih.gov/articles/PMC4865124/

 



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