Dermatomyositis and polymyositis present with these common features:

• Symmetric weakness of proximal large muscles over weeks or months. 
• As disease progresses, distal weakness can occur, resulting in dysphagia, dysphonia, head drop, and dyspnea. 
• There may be fever, arthralgia, myalgia, Raynaud’s phenomenon. 
• There may be signs and symptoms suggestive of other autoimmune diseases. 
• On clinical examination, fixed weakness is found in muscles of shoulders, arms, hips and thighs. 

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]. 

• Severe Pain

  He subsequently attended ED the following day in severe pain and bilateral sciatic symptoms, but denied symptoms of neurogenic bowel/bladder disturbance. [ncbi.nlm.nih.gov]

  The disease causes severe pain, weakness, difficulty moving and standing, chronic disability, debilitating skin rashes and other symptoms. [healio.com]

  Four months after chemotherapy, the patient complained of severe pain in her left buttock. [oadoi.org]

• Raynaud Syndrome

  Antisynthetase syndrome features include fever, nonerosive arthritis, interstitial lung disease, hyperkeratosis of the radial aspect of the digits (mechanic's hands), and Raynaud syndrome. The rash of dermatomyositis may or may not be present. [merckmanuals.com]

  Other symptoms can include shortness of breath from lung inflammation, joint pain, Raynaud’s syndrome (finger color changes and numbness in cold weather), and trouble swallowing. [arapc.com]

• Malaise

  Abrupt onset of reluctance to walk with severe lower leg pain occurs at a median of 3 days as the initial viral illness resolves.5,7,9 Common prodromal symptoms of these viral illnesses include rhinorrhea, low-grade fever, sore throat, cough, and malaise [cfp.ca]

  There is systemic upset with fever, arthralgia, malaise and weight loss. It can resemble scleroderma with Raynaud's phenomenon and dysphagia. [patient.info]

  Juvenile dermatomyositis may differ from the adult disease in the following ways: 1) The clinical presentation in children is more frequently insidious and may be dominated by constitutional symptoms of fatigue, malaise, fever, anorexia, and weight loss [annals.org]

• Aspiration

  Serial thoracic radiographs now revealed aspiration pneumonia and megaesophagus. [ncbi.nlm.nih.gov]

  Aspiration pneumonia. Difficulty swallowing may also cause you to breathe food or liquids, including saliva, into your lungs (aspiration), which can lead to pneumonia. Breathing problems. [mayoclinic.org]

  Thick white fluid was aspirated and no organisms were seen on Gram stain. The patient then reported a white discharge from his medial left knee. [ard.bmj.com]

  Patients who develop impaired swallowing, for example, are at greater risk for aspiration (inhaling food and fluids into the lungs), which causes pneumonia and may lead to death. [myositis.org]

  The highest-ranked feature of sIBM considered to contribute to death was oropharyngeal muscle dysfunction, which can lead to dysphagia and subsequently aspiration and pneumonia [ 19, 20, 22 ]. [content.iospress.com]

• Dysphagia

  BACKGROUND: Dysphagia is common in inflammatory myopathies and usually responds to corticosteroids. Severe dysphagia requiring feeding by percutaneous endoscopic gastrostomy is associated with significant morbidity and high mortality. [ncbi.nlm.nih.gov]

  You may develop dysphagia, weak wrists or fingers, and atrophy of the forearms and/or thigh muscles. Unlike other forms of myositis, inclusion-body myositis occurs more often in men than in women. [orthoinfo.aaos.org]

  These are some of the complications that may occur together with or because of myositis: Antisynthetase syndrome Calcinosis Cancer-associated myositis Cardiovascular disease Dysphagia Infection Interstitial Lung Disease Overlapping autoimmune diseases [myositis.org]

• Eruptions

  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 [symptoma.com]

  Histopathologic features seen with radiation recall or enhancement eruptions. J Cutan Med Surg 2002;6:535-40. 21. Hattangadi J, Esty B, Winey B, Duigenan S, Huang M, Yock T. Radiation recall myositis in pediatric Ewing sarcoma. [oadoi.org]

  Gottron sign A symmetrical, occasionally scaly, erythematous eruption over the extensor surfaces of the metacarpophalangeal and interphalangeal joints of the fingers, knees and elbows. [nature.com]

• Muscle Weakness

  Although his muscle weakness and CK level improved, AFL with 1:1 conduction reappeared. Therefore, radiofrequency catheter ablation (RFCA) was needed to treat the AFL, resulting in maintenance of sinus rhythm. [ncbi.nlm.nih.gov]

  Polymyositis causes muscle weakness, usually in the muscles closest to the trunk of your body. Dermatomyositis causes muscle weakness, plus a skin rash. [nlm.nih.gov]

  […] climbing stairs or rising from seated position Muscle pain and soreness Pain or weakness in joints A patchy skin rash that accompanies muscle weakness is a symptom of dermatomyositis. [barrowneuro.org]

  The combination of muscle weakness and difficulty moving can increase your risk of falling. [umiamihealth.org]

• Myalgia

  Lingual myositis Lumbar myofascial pain syndrome Maxillary myositis Muscle pain Muscle pain, abdominal Muscle tension pain Musculoskeletal pain Myalgia Myalgia (muscle pain) Myalgia/myositis - multiple Myalgia/myositis - shoulder Myofacial pain syndrome [icd9data.com]

  Muscle-strength tests revealed bilateral trivial gastrocnemius weakness with myalgia. [ncbi.nlm.nih.gov]

  See also[edit] myopathy (muscle disease) myalgia (muscle pain) Masticatory muscle myositis (a disease in dogs) perimyositis References[edit] ^ MedlinePlus Encyclopedia Myositis External links[edit] Classification D ICD-10: M60 ICD-9-CM: 729.1 OMIM: 160750 [en.wikipedia.org]

• Osteoporosis

  Common long-term effects of treatment and the chronic disease are osteoporosis, high blood pressure, diabetes, and cardiovascular disease. Therefor there is a high unmet need for new therapies. [cmm.ki.se]

  […] rheumatoid arthritis • Selected topics in systemic lupus erythematosus • Antiphospholipid antibody syndrome • IgG4-related disease • Myopathies • Selected topics in pediatric rheumatology • HIV and rheumatic diseases • Miscellaneous arthropathies • Osteoporosis [books.google.com]

  These precautions include: ● Osteoporosis prevention – A calcium supplement with vitamin D and a prescription medication to prevent osteoporosis, such as one of the bisphosphonates, are often recommended in patients treated with prednisone. [uptodate.com]

  In that case, regular check of these is required More on lungs in rheumatic diseases here If swallowing problems are present, one should eat slowly and swallow in small portions More on diet here Osteoporosis (osteoporosis) is prevented, eventually treated [bindevevssykdommer.no]

  They also noted that steroid-related adverse events were fairly common, with 12% of patients having developed diabetes and 8% having osteoporosis or hypertension. [medpagetoday.com]

• Irritability

  Myositis (my-uh-SY-tis) is inflammation of the muscles that can be caused by many conditions and diseases that make muscles weak, swollen, and irritated. [kidshealth.org]

  Chronic nerve irritation caused by compression of a nerve is another suspected cause of muscle fiber hypertrophy that consequently leads to focal myositis. [orpha.net]

  Fatigue, irritability and complaints of stomach aches often accompany muscle weakness of the proximal muscles and legs. A hoarse sounding voice or swallowing difficulties may be present. Juvenile Polymyositis (JPM) will not have a rash present. [portmelbournephysio.com.au]

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.

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:

• Inflammation:    a) Dermatomyositis, adult and juvenile and b )Polymyositis 

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 

• Infection: the most common infectious causes are of viral origin, leading to direct muscle injury or release of myotoxins. Examples of viruses that cause myopathy are common cold, influenza viruses and HIV. Other infectious causes can be bacteria, fungi or other parasites (protozoa, cestodes, nematodes). 
• Drugs: Myositis can occur as the adverse effect of certain drugs like statins, D-penicillamine, statins, zidovudine (AZT), hydroxychloroquine, hydroxyurea, interferons, L-tryptophan, colchicine, growth hormone, cocaine and alcohol. 
• Injury: Sometimes muscle damage can arise from vigorous exercise. In case of rhabdomyolysis, muscle fibers break down rapidly with release of the breakdown products into the blood which can lead to renal failure. 

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].

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].

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.

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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.