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Inflammatory Myopathy

Myositis is a term used to describe inflammation of the muscles. These conditions represent the largest group of acquired and potentially treatable causes of skeletal muscle weakness.


Dermatomyositis and polymyositis present with these common features:

Dermatomyositis has the additional cutaneous manifestations:

  • Gottron's sign (a symmetric, erythematous, scaly eruption over the metacarpophalangeal and interphalangeal joints)
  • Heliotrope eruption (periorbital erythema and edema), and 
  • Gottron’s sign (macular erythema on the elbows, knees and lateral malleoli).
  • Abdominal pain, melena or hematemesis may also be present in juvenile dermatomyositis. Malignancy is associated with 15% cases of dermatomyositis. Inclusion body myositis presents with symmetrical proximal muscle weakness in some case, and with asymmetric or distal distribution in some other. The weakness develops slowly over months to years and gradually leads to atrophy [7]. 
Buttock Pain
  • 10-CM : 729.1 converts approximately to: 2015/16 ICD-10-CM M60.9 Myositis, unspecified Or: 2015/16 ICD-10-CM M79.1 Myalgia Or: 2015/16 ICD-10-CM M79.7 Fibromyalgia Approximate Synonyms Abdominal muscle pain Benign acute myositis Buttock muscular pain Buttock[icd9data.com]
  • However, a biopsy was not possible because the patient complained of severe buttock pain, and we treated her symptoms promptly and successfully.[dx.doi.org]
Unstable Gait
  • Abstract We discuss a case of a 47-year-old man who presented with progressive proximal muscle weakness of the upper and lower extremities and unstable gait.[ncbi.nlm.nih.gov]


Needle electromyography (EMG) of muscles shows myopathic changes.
Serum levels of muscle enzymes are elevated. The most sensitive enzyme is creatine kinase (CK).
Muscle tissue biopsy shows inflammatory changes in muscle tissue. This is the definitive test for establishing the diagnosis of myositis and for excluding other neuromuscular diseases [8].
Magnetic resonance imaging is not routinely used for the diagnosis of myositis, but it may guide the location of the muscle biopsy in certain clinical settings.

Blood tests for Myositis-specific autoantibodies (MSAs) and myositis associated autoantibodies (MAAs) can be used to predict the clinical pattern and prognosis of disease.
Cancer screening: In a patient of dermatomyositis screening for malignancy should be done at initial diagnostic evaluation and yearly thereafter.

Third Degree Atrioventricular Block
  • After a second infusion with nivolumab, our patient developed a troponin I-positive and autoantibody-positive myositis and a few days later a new-onset third-degree atrioventricular block.[ncbi.nlm.nih.gov]


The goal of the treatment in myositis is to improve muscle strength and the function in activities of daily living, and ameliorate the extramuscular manifestations like rash, dysphagia, dyspnea and fever.
Drugs used in the treatment of dermatomyositis and polymyositis include:

1. Glucocorticoids. The initial treatment of choice is oral prednisone1 mg/kg per day for 3- 4 weeks, followed by tapering over a period of 10 weeks to 1 mg/kg every other day. If treatment is effective, an objective increase in muscle strength is observed within 3 months. Steroid myopathy increasing the muscle weakness even further is a possible adverse effect.

2. Immunosuppressive therapy. Lack of response to prednisone or severe side-effects are indication. The drugs used are azathioprine, methotrexate, cyclophosphamide, chlorambucil and recently, mycophenolate mofetil.

3. Immunomodulation. Intravenous immunoglobulin (IVIg) has shown good results in a controlled trial of patients with refractory dermatomyositis.
Inclusion body myositis is difficult to treat, and is generally resistant to immunosuppressive therapies. Prednisone together with azathioprine or methotrexate is often tried in newly diagnosed patients [9].


  • Polymyositis and Dermatomyositis: About 40% patients recover completely. A remitting and relapsing course is seen in 20% of patients, and the remaining have a chronic progressive disease. The skin rash of dermatomyositis sometimes does not respond to treatment as well as the myositis component. The overall five-year survival rate is 95 percent. Older age of onset, delay in start of treatment, presence of malignancy, lung and heart complications lead to poor survival [4]. 
  • Juvenile Dermatomyositis: There is a 1-2% mortality rate with 40% children having a remitting or progressive course. Around 65 - 80% children have a good functional outcome with 5% becoming wheelchair bound [5]. 
  • Inclusion Body Myositis: Survival rates are high, but functional outcome is poor, with muscle strength progressively leading to complete wheelchair dependence within 5-10 years of onset [6].


The following are the causes of myositis:

Both of the above conditions are thought to arise from autoimmunity to environmental factors, possibly triggered by viral infections or certain drugs. 

     c) Inclusion body myositis - muscle fiber degeneration arising from unknown causes.
     d )Other systemic autoimmune diseases like systemic lupus erythematosus, scleroderma and rheumatoid arthritis 


The prevalence of the myositis is estimated at 1 in 100,000. Polymyositis affects adults, peaking between 50 and 60 years, with females affected twice as much as males. Dermatomyositis affects both children and adults, with the female to male ratio being 2:1. Inclusion body myositis affects person above 50 years of age and the male to female ratio is 3:1. The mean age of onset in juvenile dermatomyositis is 7 years and the overall female to male ratio is 1.7 to 1 [2].

Sex distribution
Age distribution


In up to 20% of patients with myositis, autoantibodies against nuclear antigens (antinuclear antibodies) and cytoplasmic antigens are found. In dermatomyositis, humoral immune mechanisms are implicated in causing microangiopathy and muscle ischemia. In polymyositis and inclusion body myositis, T cell–mediated cytotoxicity is the likely mechanism. The role of a degenerative process in inclusion body myositis is demonstrated by the presence of vacuoles in unaffected fibers together with β-amyloid deposits within the vacuolated muscle fibers and abnormal mitochondria with cytochrome oxidase-negative fibers [3].


A specific method for prevention of myositis does not yet exist; therefore the focus must lie on early diagnosis and proper treatment. Any signs of muscle weakness in patients who have risk factors like ongoing treatment with statins are important to assess for early detection [10].


While there are many causes and types of myositis, the most common underlying pathophysiology is autoimmune-mediated. Other causes include injury, infection and adverse effects of drugs. The condition presents with pain, swelling and weakness of the skeletal muscles. There are different kinds of inflammatory myopathies and the treatment and prognosis depend on the cause and type [1].

Patient Information

Definition: Myositis is a chronic inflammation of muscles leading to swelling and loss of muscles, and includes diseases like polymyositis, dermatomyositis, inclusion-body myositis, and juvenile forms of myositis.
Cause: Myositis is caused by autoimmune mechanism, which means that the body’s immune system attacks the body’s own normal and healthy tissue.
Symptoms: Muscles on both sides of your body are affected leading to progressive weakness, manifesting as difficulties in rising from a chair and climbing stairs. Other symptoms may include skin rash, difficulty in swallowing, speaking or breathing, fatigue and thickening and redness of the skin on the hands.
Diagnosis: After physically examining you, the doctor will order blood tests to assess muscle enzyme levels and autoantibodies. A needle electromyography will be done to assess the nature and severity of muscle damage. A muscle biopsy will be required which involves the examination of a piece of muscle removed through a nick in the skin. Sometimes, a magnetic resonance imaging scan may be required.
Treatment and follow -up: Treatment of myositis involves suppressing the autoimmune mechanism and the resulting damage to the muscle through corticosteroid drugs like prednisone and immunosuppressive therapy. Complete and early treatment of relapses is important to limit disability and avoid serious complications related to eating and breathing.



  1. Plotz PH, Dalakas M, Leff RL, et al. Current concepts in the idiopathic inflammatory myopathies: polymyositis, dermatomyositis, and related disorders. Ann Intern Med 1989; 111:143.
  2. Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis. Lancet 2003; 362:971.
  3. jacobson DL, Gange SJ, Rose NR, Graham NM. Epidemiology and estimated population burden of selected autoimmune diseases in the United States. Clin Immunol Immunopathol 1997; 84:223.
  4. Dimachkie MM, Barohn RJ, Amato AA. Idiopathic inflammatory myopathies. Neurol Clin 2014;32(3):595-628, vii.
  5. Sultan SM, lannou V, Moss K, Isenberg DA. Outcome in patients with idiopathic inflammatory myositis: morbidity and mortality. Rheumatol 2002;41:22-26
  6. Ramanan AV, Feldman BM. Clinical features and outcomes of juvenile dermatomyositis and other childhood onset myositis syndromes. Rheum Dis Clin North Am 2002; 28:833.
  7. Cox FM, Titulaer MJ, Soni JK, et al. A 12-year follow-up in sporadic inclusion body myositis: and end stage with major disabilities. Brain 2011;134:3167-3175.
  8. Mammen AL. Dermatomyositis and polymyositis: Clinical presentation, autoantibodies, and pathogenesis. Ann N Y Acad Sci 2010; 1184:134.
  9. Smith BW, Mccarthy JC, Dawley CA. Suspect myopathy? Take this approach to the work-up. J Fam Pract 2014;63(11):631-8.
  10. Dalakas MC. Inflammatory disorders of muscle: progress in polymyositis, dermatomyositis and inclusion body myositis. Curr Opin Neurol 2004; 17:561.

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Last updated: 2019-07-11 22:44