Medicine:Polymyositis

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Polymyositis (PM) is a type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name is derived from poly- 'many', myos- 'muscle', and -itis 'inflammation'. The inflammation of polymyositis is mainly found in the endomysial layer of skeletal muscle, whereas dermatomyositis is characterized primarily by inflammation of the perimysial layer of skeletal muscles.[1]

Signs and symptoms

The hallmark of polymyositis is weakness and/or loss of muscle mass in the proximal musculature, as well as flexion of the neck and torso.[1] These symptoms can be associated with marked pain in these areas as well. The hip extensors are often severely affected, leading to particular difficulty in climbing stairs and rising from a seated position. The skin involvement of dermatomyositis is absent in polymyositis. Dysphagia (difficulty swallowing) or other problems with esophageal motility occur in as many as 1/3 of patients. Low grade fever and enlarged lymph nodes may be present. Foot drop in one or both feet can be a symptom of advanced polymyositis and inclusion body myositis. The systemic involvement of polymyositis includes interstitial lung disease (ILD) and heart disease, such as heart failure and conduction abnormalities.[2]


Associated illnesses

Polymyositis and the associated inflammatory myopathies have an associated increased risk of cancer.[3] The features they found associated with an increased risk of cancer were older age, age greater than 45, male sex, difficulty swallowing, death of skin cells, cutaneous vasculitis, rapid onset of myositis (<4 weeks), elevated creatine kinase, higher erythrocyte sedimentation rate and higher C-reactive protein levels. Several factors were associated with lower-than-average risk, including the presence of interstitial lung disease, joint inflammation/joint pain, Raynaud's syndrome, or anti-Jo-1 antibody.[3] The malignancies that are associated are nasopharyngeal cancer, lung cancer, non-Hodgkin's lymphoma and bladder cancer, amongst others.[4]

Cardiac involvement manifests itself typically as heart failure and is present in up to 77% of patients.[2] Interstitial lung disease is found in up to 65% of patients with polymyositis, as defined by HRCT or restrictive ventilatory defects compatible with interstitial lung disease.[5]

Causes

Polymyositis is an inflammatory myopathy mediated by cytotoxic T cells with an as yet unknown autoantigen, while dermatomyositis is a humorally mediated angiopathy resulting in myositis and a typical dermatitis.[6]

The cause of polymyositis is unknown and may involve viruses and autoimmune factors. Cancer may trigger polymyositis and dermatomyositis, possibly through an immune reaction against cancer that also attacks a component of muscles.[7] There is tentative evidence of an association with celiac disease.[8]

Diagnosis

Diagnosis is fourfold: History and physical examination, elevation of creatine kinase, electromyograph (EMG) alteration, and a positive muscle biopsy.[9]


Differential diagnosis

The clinical criteria of meeting a polymyositis diagnosis are non-specific, and a plethora of disorders can present with similar findings such as proximal muscle weakness, changes in lab findings (like an increase in creatine kinase), EMG findings, and muscle biopsy results.[10] The following categories summarize common and uncommon alternative diagnoses, but this list is not exhaustive.

Inflammatory and systemic autoimmune disorders

Conditions that may closely resemble polymyositis include dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy, systemic lupus erythematous, systemic sclerosis, and Sjögren syndrome. Overlapping skin features, such as facial redness/flushing in lupus, is an example of how these conditions can cause clinical confusion when diagnosing.[11]

Neuromuscular and inherited muscle disorders

Other conditions that may be confused with polymyositis include amyotrophic lateral sclerosis, chronic spinal muscular atrophy, myasthenia gravis, and inherited metabolic myopathies such as McArdle disease.[10][11]

Endocrine and metabolic disorders

Several endocrine conditions can cause proximal muscle weakness and laboratory abnormalities that mimic inflammatory myopathy. This includes thyroid issues (hypothyroidism or hyperthyroidism), where your thyroid hormones are either too high or too low. Also, it’s important to consider Cushing syndrome and acromegaly.[10][11]

Infectious causes

Parasitic infections, like Trichinella infection and sarcocystosis for example, may present with muscle pain, weakness, and inflammatory changes too. Viruses such as the influenza virus, also known as ‘the flu,’ can also cause muscle pain/weakness.[12]

Drug and toxin-associated myopathies

Medication-related muscle disease is an important diagnostic consideration. Myopathy may occur with corticosteroids, amiodarone, cyclosporine, statins, colchicine, chloroquine or hydroxychloroquine, and chronic alcohol exposure just to name a few. Some of these agents can produce muscle biopsy findings that partially overlap with inflammatory myopathies. In individuals with human immunodeficiency virus infection, both HIV-associated myopathy and antiretroviral drug toxicity may contribute to diagnostic uncertainty.[13]

Electrolyte imbalances

Electrolytes like Na, K, Ca, and P can all cause mimicking symptoms when high or low. Most commonly, hypokalemia, or low K, is the culprit, since many common drugs decrease this electrolyte.[10]

Other potential causes

Additional conditions that may present with similar clinical features include polymyalgia rheumatica, diabetic lumbosacral plexopathy, spinal stenosis, and non-inflammatory pain syndromes such as fibromyalgia.[11]

Treatment

The first line treatment for polymyositis is corticosteroids. Specialized exercise therapy may supplement treatment to enhance quality of life.[14]

Epidemiology

Polymyositis affects females at greater frequency than males.[15]

Polymyositis as a distinct diagnosis

The discovery of several myositis-specific autoantibodies during the past decades has enabled the description of other discrete subsets of diagnosis, specifically the discovery of Antisynthetase syndrome in reducing the number of diagnoses of polymyositis.[16]

Society and culture

Notable cases

  • Dan Christensen, painter of abstract art. Died due to heart failure caused by polymyositis.[17]
  • Robert Erickson, American composer and teacher who was a leading modernist exponent of "12-tone" composition. Died from the effects of polymyositis.[18]
  • Ana Estrada, the first person in Peru to die by euthanasia on 21 April 2024, at the age of 47.
  • David Lean, film director.[19][20]
  • Eric Samuelsen, playwright.[21]
  • Cardinal John Wright[22]
  • Rosita Velazquez, Puerto Rican actress and singer.[23]

See also

References

  1. ↑ 1.0 1.1 "Polymyositis-dermatomyositis: a clinical review". Postgraduate Medical Journal 65 (765): 437–43. July 1989. doi:10.1136/pgmj.65.765.437. PMID 2690042. 
  2. ↑ 2.0 2.1 "Cardiac involvement in adult polymyositis or dermatomyositis: a systematic review". Clinical Cardiology 35 (11): 686–91. November 2012. doi:10.1002/clc.22026. PMID 22847365. 
  3. ↑ 3.0 3.1 Xin Lu; Hanbo Yang; Xiaoming Shu; Fang Chen; Yinli Zhang; Sigong Zhang; Qinglin Peng; Xiaolan Tian et al. (2014). "Factors Predicting Malignancy in Patients with Polymyositis and Dermatomyositis: A Systematic Review and Meta-Analysis". PLOS ONE 9 (4). doi:10.1371/journal.pone.0094128. PMID 24713868. Bibcode: 2014PLoSO...994128L. 
  4. ↑ Hill, C.L.; Zhang, Y.; Sigurgeirsson, B.; Pukkala, E.; Mellemkjaer, L.; Airio, A.; Evans, S.R.; Felson, D.T. (January 2001). "Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study". Lancet 357 (9250): 96–100. doi:10.1016/S0140-6736(00)03540-6. PMID 11197446. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(00)03540-6/abstract. Retrieved 20 April 2015. 
  5. ↑ "Interstitial lung disease, a common manifestation of newly diagnosed polymyositis and dermatomyositis". Annals of the Rheumatic Diseases 63 (3): 297–301. March 2004. doi:10.1136/ard.2003.006122. PMID 14962966. 
  6. ↑ Gerald J D Hengstman, Baziel G M van Engelen (2004). "Polymyositis, invasion of non-necrotic muscle fibres, and the art of repetition". British Medical Journal 329 (7480): 1464–1467. doi:10.1136/bmj.329.7480.1464. PMID 15604185. 
  7. ↑ Hajj-ali, Rula A. (August 2013). "Polymyositis and Dermatomyositis". Merck Manual Home Edition. http://www.merckmanuals.com/home/bone-joint-and-muscle-disorders/autoimmune-disorders-of-connective-tissue/polymyositis-and-dermatomyositis. 
  8. ↑ "Neurological Complications of Gastrointestinal Disease.". Semin Pediatr Neurol 24 (1): 43–53. 2017. doi:10.1016/j.spen.2017.02.001. PMID 28779865. 
  9. ↑ "Diagnosis of dermatomyositis and polymyositis: a study of 102 cases". Arquivos de Neuro-Psiquiatria 58 (3B): 789–99. September 2000. doi:10.1590/S0004-282X2000000500001. PMID 11018813. 
  10. ↑ 10.0 10.1 10.2 10.3 "A Physician's Guide to Myositis". 2018. https://www.myositis.org/wp-content/uploads/2018/01/PhysiciansGuide.pdf. 
  11. ↑ 11.0 11.1 11.2 11.3 Sarwar, Ayesha; Dydyk, Alexander M.; Jatwani, Shraddha (2025), "Polymyositis", StatPearls (Treasure Island (FL): StatPearls Publishing), PMID 33085276, http://www.ncbi.nlm.nih.gov/books/NBK563129/, retrieved 2026-02-09 
  12. ↑ Crum-Cianflone, Nancy F. (July 2008). "Bacterial, fungal, parasitic, and viral myositis". Clinical Microbiology Reviews 21 (3): 473–494. doi:10.1128/CMR.00001-08. ISSN 1098-6618. PMID 18625683. PMC 2493084. https://pmc.ncbi.nlm.nih.gov/articles/PMC2493084/. 
  13. ↑ Miernik, Sebastian; Matusiewicz, Agata; Olesińska, Marzena (2024-04-30). "Drug-Induced Myopathies: A Comprehensive Review and Update". Biomedicines 12 (5): 987. doi:10.3390/biomedicines12050987. ISSN 2227-9059. PMID 38790948. PMC 11117896. https://pmc.ncbi.nlm.nih.gov/articles/PMC11117896/. 
  14. ↑ "Myositis". https://medlineplus.gov/myositis.html. 
  15. ↑ "Signs and Symptoms of Polymyositis (PM) - Diseases" (in en). 2015-12-18. https://www.mda.org/disease/polymyositis/signs-and-symptoms. 
  16. ↑ Leclair, Valérie; Notarnicola, Antonella; Vencovsky, Jiri; Lundberg, Ingrid E. (November 2021). "Polymyositis: does it really exist as a distinct clinical subset?". Current Opinion in Rheumatology 33 (6): 537–543. doi:10.1097/BOR.0000000000000837. PMID 34494607. 
  17. ↑ "Dan Christensen, 64, Painter of Abstract Art, Dies". The New York Times. 27 January 2007. https://www.nytimes.com/2007/01/27/obituaries/27christensen.html. 
  18. ↑ "Obituary - Robert Erickson". SF Gate. 29 April 1997. http://www.sfgate.com/news/article/OBITUARY-Robert-Erickson-2842509.php. 
  19. ↑ Stevens, George Jr. (2006). Conversations with the Great Moviemakers of Hollywood's Golden Age at the American Film Institute. Knopf. p. 427. ISBN 978-1-4000-4054-4. 
  20. ↑ Brownlow, Kevin (1996). David Lean: A Biography. Macmillan. pp. 1466–1467. ISBN 978-1-4668-3237-4. https://books.google.com/books?id=u4AdbfjHZf0C&pg=PT1466. Retrieved 20 April 2015. 
  21. ↑ "Noted Latter-day Saint playwright and LGBT ally Eric Samuelsen dies" (in en-US). https://www.sltrib.com/artsliving/2019/09/20/noted-lds-playwright-eric/. 
  22. ↑ Vecsey, George (1979-08-12). "John Cardinal Wright Dies at 70; Top-Ranking American in Vatican" (in en-US). The New York Times. ISSN 0362-4331. https://www.nytimes.com/1979/08/12/archives/john-cardinal-wright-dies-at-70-topranking-american-in-vatican-saw.html. 
  23. ↑ "Rosita Velázquez". https://prpop.org/biografias/rosita-velazquez/. 
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