Polymyositis is an inflammatory disease of muscles, causing weakness in the muscles closest to the torso — usually the shoulder and hip muscles. It is an autoimmune disorder, meaning that a person’s white blood cells begin attacking muscles for an unknown reason. The disease is chronic, but the symptoms may come and go. Anyone can get polymyositis, but it is slightly more common in females, and people in middle childhood and their 20s. It is sometimes connected with cancer, scleroderma, and rheumatoid arthritis

Polymyositis Symptoms

Polymyositis is an inflammatory disease of muscles, which causes muscle weakness. This weakness usually develops slowly over weeks to months although rare cases can begin over days. This weakness most commonly affects the muscles of the arms and legs. Patients often notice trouble getting out of chairs or climbing stairs. It does not typically involve the muscles of the eyes, heart, or breathing muscles. However the muscles involved in swallowing can become weak as well. Muscle pain may also be a prominent symptom since polymyositis is associated with inflammation in the muscles.

The diagnosis of polymyositis begins with a neurologist taking the patient’s history. A physician who suspects a diagnosis of polymyositis may perform blood tests, an EMG, or a magnetic resonance imaging scan (MRI). The blood tests reveal elevated levels of enzymes which are found in muscle. Doctors may check a creatine phoshpokinase (CPK) or an aldolase. Without elevated levels of one of these enzymes it is very unlikey to have a diagnosis of polymyositis. The EMG test looks at the function of a patient’s muscles and will reveal evidence for muscle inflammation and muscle damage. An MRI looks for visual evidence for inflammation in a group of muscles. It can also be used to choose which muscle to biopsy.

If these three non-invasive tests suggest a diagnosis of polymyositis then patients should have a muscle biopsy before beginning therapy. This is important because many disease can look like polymyositis but in fact may represent forms of muscular dystrophy or another related disease called Inclusion Body Myositis. This distinction is important because polymyositis is treatable but muscular dystrophy and inclusion body myositis are not treatable. Therefore, a muscle biopsy is needed in all patients for a definitive diagnosis. Finally there are a very specific set of blood tests called Myositis Specific Autoantibodies. These antibodies are found in 20-30% of patients with polymyositis but are important because they can predict the presence of other associated conditions.

Polymyositis Cause

Polymyositis is an autoimmune disorder, meaning that a person’s white blood cells which are supposed to fight off bacteria and viruses begin attacking their own muscles. While we do not know what triggers a person’s immune system to behave in this way ,there are many theories that suggest the cause of Polymyositis is a combination of one’s genetic predisposition and environmental exposures. People of either sex or any age can get polymyositis, but it is slightly more common in females, and people in middle childhood and their 20s. It is sometimes associated with other autoimmune diseases such as sometimes connected with lupus, scleroderma, and rheumatoid arthritis. In rare cases it can be associated with certain types of cancers.

Syndrome Distinctive features
Idiopathic Proximal weakness; High CK; Inflammatory myopathy
Collagen vascular disease Myalgias; Younger onset Scleroderma & Mixed connective tissue disease
Anti-t-rna synthetase antibodies Jo-1 antibodies Interstitial pneumonitis; Raynauds; Arthritis Perimysial pathology
Signal recognition particle antibody Acute onset; Severe weakness Capillary pathology; Fibrosis
MAS antibody Acute onset; Rhabdomyolysis
Drug-induced D-penicillamine
Familial Homozygosity at HLA-DQA1 locus
Graft-vs-host disease 7 to 24 months post BMT
Granulomatous Sarcoid; Immune; Infections
Sarcoidosis Myopathy; Neuropathy; Lung disease
Malignancy (Necrotic) Rapid onset; Older patients; Necrotic myopathy
Mitochondrial (P-COX) Quadriceps weakness; Older onset age; Steroid resistant
Other systemic disorders HIV; Fasciitis

Polymyositis Treatment

Polymyositis is an autoimmune disease and therefore therapy is directed at altering a patient’s immune system. All of these therapies therefore have some significant risk of side effects and Polymyositis treatment needs to be undertaken only with physicians accustomed to using these medications and to monitoring their side effects. Corticosteroids are often used as a first line therapy to treat polymyositis because they decrease the muscle inflammation. These can be effective in a matter of weeks. If corticosteroids are ineffective, other immunosuppressive medications may be given such as azathioprine, mycophenylate mofetil, cyclosporine, or methotrexate. Intravenous immunoglobulin has also been shown to be effective in very refractory cases.

Polymyositis Cure

In most people once this disease begins there is no clear way to cure Polymyositis. There are however several effective treatments which exist that can improve a person’s muscle strength. In most cases people can resume their usual level of function. Further research is being done and it is hopeful that within years a cure for polymyositis will be found.

Polymyositis Research

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