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Polymyositis

PM

Polymyositis is a rare progressive inflammatory disease of skeletal muscle characterized by symmetrical weakness, pain and tenderness.


Presentation

People with polymyositis often do not experience symptoms at the onset of immune-mediated muscle cell damage. Weakness occurs when at least 50% of muscle cells become damaged, so the patient experiences progressive muscle weakness spanning three to six months. In polymyositis, the muscle weakness is always symmetrical and the areas of involvement may fluctuate from time to time. Unlike in dermatomyositis, skin rash is rare in polymyositis.

A patient with polymyositis may be unable to perform motor functions due to muscle weakness. Things like getting up from a chair, climbing stairs or lifting become difficult. The patient may also complain difficulty on swallowing and lifting the head as the flexor muscles of the neck becomes affected. Some cases of polymyositis have manifestations of muscle weakness in the orbital muscles. Rare cases also have weaknesses in facial and bulbar muscles.

Aside from muscle weakness, a person with polymyositis may or may not experience myalgia. Polymyositis patients may also experience other symptoms such as morning stiffness, fatigue and anorexia, fever and weight loss. In addition, people with polymyositis may also have arthralgia and arthritis [6].
Polymyositis can also manifest symptoms like nasal regurgitation, reflux esophagitis, bloating and constipation and odynophagia.

Rarely, kidney problem is present in polymyositis. In some cases, polymyositis can affect the muscles of the heart. The patient may suffer from arrhythmias, conduction defects and myocarditis and pericarditis. People with polymyositis may suffer from serious heart problems like pulmonary hypertension and congestive heart failure. Dyspnea is also seen in rare cases of polymyositis, which is caused by weakening of muscles involved in breathing.
The patient may be unable to execute fine motor movements in later stages of the disease. Symptoms of dysphagia and dysphonia are often signs of poor prognosis.

Patients with polymyositis may also have chronic connective tissue disorders such as Sjögren syndrome, rheumatoid arthritis, lupus, mixed-connective tissue disease and scleroderma.

Purulent Sputum
  • We expose the case of a young woman (47 years old) who presented to the Pulmonology Clinic with fever, cough, purulent sputum, discrete myalgia, being diagnosed at that moment with interstitial lung disease and treated with antibiotics, low dose of corticosteroids[ncbi.nlm.nih.gov]
Fatigue
  • Muscle weakness versus fatigue It may be easy to confuse muscle weakness with the general feeling of tiredness and weariness caused by fatigue. Both symptoms can occur as a result of polymyositis. Muscle weakness is a loss of strength.[dmpmandyou.com]
  • Related Reading: Myasthenia gravis, a neuromuscular disease, causes voluntary muscle weakness and fatigue Myasthenia gravis, a neuromuscular disease, causes voluntary muscle weakness and fatigue.[belmarrahealth.com]
  • Fatigue Difficulty swallowing or speaking Shortness of breath As the symptoms of polymyositis worsen, it may become difficult to raise your head when lying down, or to stand up from a seated position.[muirortho.com]
  • Disabling Symptoms of Polymyositis and Dermtomyositis Symptoms of polymyositis and dermtomyositis can include: muscle weakness, usually close to the trunk of the body fatigue, and shortness of breath.[disabilitysecrets.com]
  • There are periods, sometimes days, sometimes weeks, when I feel well, my pain levels are low, and my fatigue is manageable; however, I have to be careful not to overdo things, or the pain and fatigue soon return.[bmj.com]
Weight Loss
  • […] rashes on connective skin (Gottron’s papules/sign) Roughened, dry skin on palms and fingers (mechanic’s hands) Polymyositis Gradual onset of proximal muscle weakness Fatigue, general discomfort, weight loss, low-grade fever Acthar is an FDA-approved[actharrheumatology.com]
  • Clinical signs include depression, lethargy, weakness, weight loss, lameness, myalgia, and muscle atrophy. CK may be increased, and electromyography reveals abnormal spontaneous muscle activity.[merckvetmanual.com]
  • She also reports fatigue and weight loss. Physical examination shows 3/5 muscle strength in the proximal upper extremities bilaterally and 4/5 throughout the lower extremities bilaterally. She states that she can no longer climb the stairs at home.[osmosis.org]
  • In addition to progressive muscle weakness, swelling and tenderness, people with polymyositis may have shortness of breath, fatigue, joint pain, fever, difficulty swallowing or speaking, loss of appetite, and weight loss.[kidshealth.org]
Fever
  • Familial Mediterranean fever (FMF) is an autosomal recessive disease affecting populations surrounding the Mediterranean area. In this case report, we report a Japanese female patient with polymyositis (PM) who presented with periodic fever.[ncbi.nlm.nih.gov]
  • A 71-year-old woman with polymyositis presenting with left thigh pain and an intermittent fever was admitted to Osaka Rosai Hospital.[ncbi.nlm.nih.gov]
  • He presented cutaneous abscesses and fever months after the tuberculosis regimen. The patient was diagnosed as metastatic tuberculous abscesses associated with immunosuppression as result of polymyositis treatment.[ncbi.nlm.nih.gov]
  • A 13-year-old girl was admitted for persistent thigh pain and remittent fever and was diagnosed as having juvenile polymyositis.[ncbi.nlm.nih.gov]
  • On approximately day 1,570 post HLA-identical sibling bone marrow transplant, the patient presented with a fever, myalgia and liver dysfunction.[ncbi.nlm.nih.gov]
Raynaud Phenomenon
  • Myositis was associated with Raynaud's phenomenon, mild sclerodactyly, and anti-Ku antibodies leading to the diagnosis of polymyositis/systemic sclerosis overlap myositis. The posture showed modest improvement in response to treatment.[ncbi.nlm.nih.gov]
  • A clinical examination revealed Raynaud phenomenon, arthralgia, distal skin sclerosis, and microbleeds in the nailfold capillaries. An anti-Ku antibody test was positive. A muscle biopsy revealed inflammatory myopathy with rimmed vacuoles (RVs).[ncbi.nlm.nih.gov]
  • Other symptoms of PM may include fever, weight loss, fatigue, joint pain and Raynaud phenomenon which is a sensitivity to the cold that is most often felt in the fingers.[rarediseases.org]
  • You may also have: Fever Weight loss Fatigue Joint pain Raynaud’s phenomenon, a condition in which the fingers or toes become very cold and discolored due to blood -flow problems. Diagnosis There are no simple tests to diagnose polymyositis.[webmd.com]
Difficulty Climbing Stairs
  • Progressive muscle weakness starts in the proximal muscles (muscles closest to the trunk of the body) which eventually leads to difficulties climbing stairs, rising from a seated position, lifting objects, or reaching overhead.[ninds.nih.gov]
  • As the disease progresses and muscle power is lost, patients may experience a range of symptoms, including: Muscle weakness, usually in those that are closest to the body's trunk Loss of strength, difficulty climbing stairs, getting up from a chair, or[tuh.templehealth.org]
  • She states that she now has difficulty climbing stairs and extending her neck. Ultimately, she became more concerned when she began having trouble swallowing and experienced shortness of breath.[step2.medbullets.com]
  • You’ll have difficulty climbing stairs, getting up from a chair, or lifting objects with your arms. Fatigue, on the other hand, is more or less feeling like you simply cannot get out of bed all day. Both of these symptoms can be troublesome.[dmpmandyou.com]
Muscle Weakness
  • Pulmonary involvement in polymyositis includes respiratory muscle weakness, aspiration pneumonia, interstitial lung disease, infection and drug-induced pneumonia.[ncbi.nlm.nih.gov]
  • Polymyositis-like syndrome in hypothyroidism is a rare condition characterised by proximal muscle weakness and elevated muscle enzymes.[ncbi.nlm.nih.gov]
  • Polymyositis is an immune-mediated myopathy with clinical features of proximal muscle weakness. Dysphagia and neck flexor weakness can develop along with respiratory muscle weakness as the disease progresses.[ncbi.nlm.nih.gov]
  • Polymyositis is an idiopathic inflammatory myopathy, characterized by proximal muscle weakness and sometimes extramuscular manifestations.[ncbi.nlm.nih.gov]
  • These treatments finally improved the muscle weakness and activities of daily living, and the two patients were discharged after recovery.[ncbi.nlm.nih.gov]
Myopathy
  • Drug interactions increase the risk of statin-associated toxic myopathy, but no risk factors for statin-associated inflammatory myopathies have been established.[ncbi.nlm.nih.gov]
  • CONCLUSIONS Our case illustrates that severe muscle pain may be the initial feature of Miyoshi myopathy and should be considered in the differential diagnosis of inflammatory myopathies.[ncbi.nlm.nih.gov]
  • However, muscle weakness and the disability progressed due to steroid myopathy, and subsequent oral intake became impossible because of swallowing disturbance in these two patients.[ncbi.nlm.nih.gov]
  • We herein attempted to determine the features and etiologies of these myopathies.[ncbi.nlm.nih.gov]
  • Only five cases of camptocormia secondary to idiopathic inflammatory myopathies have been described in the literature.[ncbi.nlm.nih.gov]
Proximal Muscle Weakness
  • Polymyositis-like syndrome in hypothyroidism is a rare condition characterised by proximal muscle weakness and elevated muscle enzymes.[ncbi.nlm.nih.gov]
  • Polymyositis is an immune-mediated myopathy with clinical features of proximal muscle weakness. Dysphagia and neck flexor weakness can develop along with respiratory muscle weakness as the disease progresses.[ncbi.nlm.nih.gov]
  • Polymyositis is an idiopathic inflammatory myopathy, characterized by proximal muscle weakness and sometimes extramuscular manifestations.[ncbi.nlm.nih.gov]
  • Polymyositis is an idiopathic inflammatory myopathy of unknown aetiology that affect skeletal muscles causing symmetrical, proximal muscle weakness, and also other internal organs.[ncbi.nlm.nih.gov]
  • Herein, we report the first case of PM with elevated serum IgG4 levels and IgG4 plasma cells in the muscles, mimicking IgG4-RD.A 73-year-old woman visited our hospital because of proximal muscle weakness of both thighs.[ncbi.nlm.nih.gov]
Myalgia
  • The evolution was slowly favorable for the respiratory impairment, but the patient developed exacerbated myalgia, muscle weakness, reaching even the impossibility of maintaining orthostatism, and also joint pain.[ncbi.nlm.nih.gov]
  • This report highlights the case of a 30-year-old male who had severe myalgia and proximal muscle weakness. In addition to raised creatinine phosphokinase (CPK) levels, his biochemical profile showed hypothyroidism.[ncbi.nlm.nih.gov]
  • On approximately day 1,570 post HLA-identical sibling bone marrow transplant, the patient presented with a fever, myalgia and liver dysfunction.[ncbi.nlm.nih.gov]
  • The patient developed fever and generalized myalgia 22 days after a single dose of DLI. Laboratory testing showed elevated muscle enzymes and myopathic abnormalities on electromyographic examination.[ncbi.nlm.nih.gov]
  • Myalgia means muscle pain or aching. An example of a myalgia would be the ailment fibromyalgia .[belmarrahealth.com]
Muscle Tenderness
  • The result of this attack on the muscles is inflammation, with muscle tenderness as an occasional complaint. The onset of symptoms may be acute, but the condition usually progresses slowly.[bcm.edu]
  • People with polymyositis often complain of joint and muscle tenderness. There is no cure for polymyositis. Corticosteroids are used to suppress the immune system as well as other drugs classified as immunosuppressants.[livestrong.com]
  • Mild joint or muscle tenderness. Fatigue. Causes - Polymyositis Polymyositis belongs to a group of conditions called inflammatory myopathies. Myopathies are diseases or abnormal conditions of the muscles.[checkorphan.org]
Limb Weakness
  • Examination revealed multiple telangiactasia over face and nail beds and bilateral proximal lower limb weakness of power 4/5.[ncbi.nlm.nih.gov]
  • In her history, she had upper and lower limbs weakness accompanied by dysphagia which was further complicated by right bronchial aspiration 9 months ago.[ncbi.nlm.nih.gov]

Workup

There is no single test that can prove diagnosis of polymyositis. Polymyositis is regarded as a diagnosis of exclusion because it affects several organ systems and has different symptoms. A person with polymyositis may also have other myopathy and connective tissue disorders.

Diagnosis of polymyositis is further complicated because its symptoms tend to resemble other myopathies or conditions such as lupus, Cushing syndrome or multiple sclerosis, causing it to become frequently misdiagnosed.

Different and several laboratory tests are used to determine if the patient has polymyositis. Complete blood counts can reveal leukocytosis or thrombocytosis. 50% of polymyositis patients have leukocytosis, positive Rh factor and elevated erythrocyte sedimentation rate (ESR). Myoglobinuria is often present.

Electromyography findings are often used as one of the confirmatory tests for polymyositis. It is used to determine extent of muscle damage in patients with polymyositis. Findings are almost always abnormal, with evidence of membrane irritability, fibrillation potentials, myopathic changes of motor unit action potential, increased polyphasic potentials and bizarre high-frequency repetitive discharges, and evidence of denervation-reinnervation.

Muscle biopsy findings often supports diagnosis of polymyositis, and it helps determine it from other muscle diseases. Electromyography is often first used to determine best sites for muscle biopsies for diagnosis because polymyositis tends to involve patches of muscles. Muscle biopsy findings consistent with polymyositis include presence of inflammation, necrosis and regeneration of muscle fibers, plus focal endomysial infiltration by mononuclear cells; CD8 T lymphocytes and macrophages. Capillary obliteration, endothelial cell damage and increased presence of connective tissue may also be present. In late stage polymyositis, muscle biopsy findings consist of degeneration of muscle cells, fibrosis and presence of regeneration. These findings, along with elevated creatine kinase, confirm the diagnosis of polymyositis.

Patients with polymyositis tend to have elevated serum creatine kinase (CK), usually 5-50 times the reference range. CSK levels greater than 100 times the normal levels are indicative of other conditions. Polymyositis patients may also have elevated lactic dehydrogenase, aspartate aminotransferase and alanine aminotransferase.

Polymyositis patients may exhibit specific antibody findings. Myositis-specific antibodies are often present in patients with polymyositis. Antinuclear antibody assay is also present in one-third of polymyositis cases. Other antibodies that may be present in polymyositis patients include antisynthetase antibodies such as anti-Jo-1 antibodies and Signal-recognition particle (SRP) antibodies.

Imaging studies like magnetic resonance imaging (MRI), chest radiography and high-resolution computerized tomography (CT) is used to determine extent of muscle involvement in patients with polymyositis. MRI is especially useful in scanning muscle inflammation, edema and scarring, and is also used to guide muscle biopsy procedures and monitor disease progression. Chest x-rays and CT scans are used to assess presence of lung disease and possible malignancies.

Patients with diagnosed or suspected polymyositis must be assessed for malignancy. Mammography, pelvic ultrasonography and upper- and lower-endoscopy procedures are used to screen for any associated malignancies.

Mediastinal Mass
  • Chest CT scan showed a mediastinal mass suggestive of thymoma. Muscle biopsy revealed giant cell polymyositis.[ncbi.nlm.nih.gov]
Elevated Sedimentation Rate
  • sedimentation rate (ESR) of 50 - 100 in 40% and an ESR above 100 in 10% ( Ann Rheum Dis 1993;52:857 ) Radiology description MRI T2 may show edema, which is useful in muscle biopsies Prognostic factors Response to therapy is variable - older patients[pathologyoutlines.com]
Muscle Biopsy Abnormal
  • A diagnosis of classic or definite polymyositis or dermatomyositis (Critieria A and B plus at least one of the three other criteria): Symmetrical proximal muscle weakness; Muscle biopsy abnormalities at some time during their disease: i. degeneration[clinicaltrials.gov]

Treatment

There is no exact cure for polymyositis. Cases of polymyositis tend to have different presentations, so the mainstay of treatment is to address the symptoms.

Another reason why treatment is empirical is because only few randomized clinical trials have been conducted to determine best treatment courses for polymyositis.

Since polymyositis is caused by a faulty immune system, drugs that can suppress the activity of the immune system are used for treatment. Corticosteroids like prednisone are used to suppress inflammation to help damaged muscle cells recuperate. High dose is usually maintained for 4 to 8 weeks until creatinine kinase levels go down. Then the dose of prednisone is tapered gradually to minimum therapeutic levels. If effective, the patient may need to take corticosteroids for years. Corticosteroids may not work for everyone, and may cause undesirable adverse effects like changes in personality, swellings of the extremities, acne, cataracts, osteoporosis, diabetes and hypertension.

Immunosuppressants are used to reduce the activity of the nervous system, and they are indicated for cases of polymyositis unresponsive to corticosteroids and for late-stage cases with difficulty in swallowing or speaking. Some examples of immunosuppressants used for polymyositis include azathioprine, cyclophosphamide, methotrexate, chlorambucil, and cyclosporine. Because immunosuppressants can lower down the ability of the immune system to respond against disease-causing pathogens, the patient needs to be protected against infection. Many immunosuppressive drugs also have strong side effects.
Intravenous immunoglobulin and tumor necrosis factor (TNF) has demonstrated efficacy in treatment of refractory cases of polymyositis. Agents like rituximab (anti-CD20 monoclonal antibody) and interferon Alfa-2A are also considered for management of treatment-resistant polymyositis.

Both corticosteroids and immunosuppressants can exert undesirable adverse effects and complications. Therefore, doctors additionally recommend supplementary vitamins and minerals and order frequent lab tests to assess for problems caused by medications.

Plasmapheresis may be used in polymyositis to remove inflammation-causing antibodies in the blood.

Aside from medicines, physical therapy is used for treatment of polymyositis to counter muscle weakness. The goals of physical therapy are to gradually strengthen the muscles and prevent disability. A supervised exercise program may be instituted to improve muscle strength and improve range of motion.

Development of contractures due to muscle weakness may be countered with application of splints. There is a clear need to rehabilitate atrophied muscles after flares ended. Active range-of-motion exercises and isometric contractions can help bring back control on atrophied muscles, and when enough strength has returned, light resistance exercises are then instituted for continued improvement.

Prognosis

Polymyositis can have different prognosis on patients [8]. Some patients only experience brief episodes of muscle weakness followed by a remission that may not require further treatment. Others experience repeated alternating episodes of flares and remissions. But most patients with polymyositis respond to therapy.

Some patients with poor prognosis experience progressive muscle weakness, especially in crucial areas like the heart, chest and throat, causing heart failure, respiratory ammonia, or malnutrition and cachexia.

Etiology

Polymyositis is caused by an abnormal immune system. In polymyositis, a type of white blood cell called cytotoxic T-cells attack skeletal muscles to cause symptoms. Experts are still unsure how and why T-cells turn and attack healthy and indigenous skeletal muscle cells. According to available evidence, this adverse immune response may be caused by or is associated with viral infections, possible malignancies, autoimmune or connective tissue disorders [4].

Some studies suggests that polymyositis occurs when the T-cells induce a cytotoxic response to some unidentified antigens found in muscle cells. There is also an evidence of autoimmune response to these antigens in muscle cells. It is postulated that these antigens may be a result of an unknown viral infection to the muscle cells, provoking the immune system to attack it. The presence of antibodies specific to these unknown antigens has also been found in some patients. There may be also a genetic link that makes some people predisposed to polymyositis.

Some medical conditions, such as hepatitis B, Coxsackievirus B1, influenza and adenovirus, may increase risk of having polymyositis. Drugs such as hydroxychloroquine and colchicine may also increase risk of metabolic myopathy, though they rarely induce immune-mediated myopathy [5].

Epidemiology

Polymyositis is an incredibly rare medical condition. There are only few studies that examined the prevalence of polymyositis. Estimates show that there are only 50 cases of polymyositis for every million people in the United States [2]. In a Quebec-based study, hospital and billing records show that there are only estimated 21.5 polymyositis cases for every 100,000 people [3].
Both polymyositis and dermatomyositis are more commonly seen in females and in adults. Cases of polymyositis are very rare in patients below 18 years of age.

Sex distribution
Age distribution

Pathophysiology

Polymyositis happens when the white blood cells invokes an abnormal immune response that targets skeletal muscle cells, causing progressive inflammation that causes to cellular damage. Normally, white blood cells attack foreign and disease-causing pathogens to protect us from disease. Due to some unknown reason, white blood cells attack the healthy skeletal muscle cells [6].

The resulting damage causes inflammation in the muscle cells that results to atrophy and loss of ability to contract. The patient then experiences symptoms of profound muscle weakness once enough numbers of muscle cells have been affected. Leucocytes affects more and more healthy muscle cells, so more muscle groups becomes weak over time.

Polymyositis always affects the muscles nearest to the trunk first, and then gradually progresses outward until remission occurs.

Prevention

There are no guidelines for prevention of polymyositis.

Summary

Polymyositis is a medical condition wherein the skeletal muscles experiences persistent inflammation that leads to muscular weakness. Polymyositis is somewhat similar to a condition called dermatomyositis, which affects both the skin and muscles. Both conditions are termed as idiopathic inflammatory myopathies [1].
In polymyositis, the leucocytes attacks skeletal muscle cells in the same way it attacks foreign pathogens, causing inflammation that causes the affected muscles to lose muscle tone and thus unable to contract.

Polymyositis tends to produce symmetrical weakness on muscles proximal to the trunk. People with polymyositis experience progressive muscle weakness (or flares), and only few cases experience periods of minimal symptoms (or remission).

Aside from the skeletal muscles, a person with polymyositis may experience other symptoms and have problems to other organs as well. In addition, polymyositis is linked to certain cancers in the ovaries, lung, pancreas, stomach and colon and lymph nodes.
Polymyositis exclusively affects adults, and has a tendency for females rather than males. Polymyositis is a chronic illness, and the bouts of severe muscle weakness can be debilitating at times.

Patient Information

Polymyositis is a medical condition wherein, for unknown reasons, the white blood cells that are supposed to defend the body from disease-causing pathogens attacks normal and healthy muscle cells in the body. Aside from muscle involvement, patients with polymyositis may have other problems in the organs.

Polymyositis belongs to a class of medical conditions called myopathies, and it shares many symptoms with other conditions such as dermatomyositis. And like most myopathies, polymyositis can last for a long period of time. Polymyositis is very rare, and tends to be confined to adults and more common in females.
The exact mechanism on how white blood cells attach normal muscle cells and cause polymyositis is not well understood.

Unknown viral infections, undetected malignancies, disorders in the immune system or connective tissues may make white blood cells turn against muscle cells that cause polymyositis. Regardless of the cause, the white blood cells attack the muscle cells and cause inflammation that results to muscle wasting

A lot of patients with polymyositis also have other conditions including lupus, multiple sclerosis, Cushing syndrome and chronic viral infections like hepatitis B. Polymyositis is also linked to cancers in the ovaries, lungs, colon and lymph nodes and other organs. Therefore, if you have polymyositis you must be regularly screened for presence of cancer.

The main symptom of polymyositis is progressive muscle weakness that spreads outward from the trunk, on both sides of the body. The patient may also experience other symptoms like muscle and joint pains, and kidney problems. The resulting muscle weakness may also make you unable to swallow, speak, move your head or even speak.

Because the symptoms of polymyositis are somewhat same with other conditions, and because it concurrently occurs with other medical conditions, diagnosing is somewhat a challenge. Several different lab tests and imaging studies are required in diagnosis of polymyositis.

The prognosis of polymyositis can vary among patients. Some may only experience brief muscle weakness followed by recovery with no need for more treatment, while others may experience prolonged and progressive muscle weakness plus complications.

References

Article

  1. Choy EHS, Isenberg DA. Treatment of dermatomyositis and polymyositis, Rheumatology. 2002· 41 (1): 7-13.
  2. Hill CL, Zhang Y, Sigurgeirsson B, Pukkala E, Mellemkjaer L, Airio A, Evans SR, Felson DT. Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study, Lancet. 2001; Jan 13;357(9250):96-100.
  3. Bernatsky S, Joseph L, Pineau CA, Bélisle P, Boivin JF, Banerjee D, Clarke AE. Estimating the prevalence of polymyositis and dermatomyositis from administrative data: age, sex and regional differences, Ann Rheum Dis; 2009 Jul;68(7):1192-6.
  4. Hunter K, Lyon MG. Evaluation and management of polymyositis. Indian J Dermatol. 2012 Sep;57(5):371-4.
  5. Aisa Y. et al. Polymyositis, pulmonary fibrosis and malignant lymphoma associated with hepatitis C virus infection. Intern Med. 2001 Nov;40(11):1109-12.
  6. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis, Lancet 2003; 362: 971-82.
  7. Dorph C, Englund P, Nennesmo I, Lundberg IE. Signs of inflammation in both symptomatic and asymptomatic muscles from patients with polymyositis and dermatomyositis. Ann Rheum Dis. 2006 December; 65(12): 1565–1571.
  8. Airio A, Kautiainen H, Hakala M. Prognosis and mortality of polymyositis and dermatomyositis patients. Clin Rheumatol. 2006 Mar;25(2):234-9

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Last updated: 2017-08-09 17:31