What is the definition of Polymyositis?

Polymyositis is a type of inflammatory myopathy, which refers to a group of muscle diseases characterized by chronic muscle inflammation and weakness. The muscles affected by polymyositis are the skeletal muscles (those involved with making movements) on both sides of the body. Although the disease can affect people of all ages, most cases are seen in adults between the ages of 31 and 60 years. The disease is more common among women and among black individuals. 

The exact cause of polymyositis is unknown. The disease shares many characteristics with autoimmune disorders, which occur when the immune system mistakenly attacks healthy body tissues. In some cases, the disease may be associated with viral infections, connective tissue disorders, or an increased risk for malignancies (cancer). Diagnosis is based on a clinical examination that may include laboratory tests, imaging studies, electromyography, and a muscle biopsy. Although there is no cure for polymyositis, treatment with corticosteroids or immunosuppressants can improve muscle strength and function.

What are the causes for Polymyositis?

The exact cause of polymyositis is unknown. The disease is thought to be related to problems with the immune system, and the disease shares many similarities with autoimmune diseases. An autoimmune disease occurs when the immune system mistakenly attacks healthy body tissues. It appears that the cells of the muscles (muscle fibers) of individuals with polymyositis are not protected from the body’s immune system. Therefore, the immune system can attack the muscle fibers, which causes them to become damaged, inflamed, and weakened. 

For some people, symptoms of polymyositis may be associated with connective tissue disorders, viral infections such as HIV-AIDS, other autoimmune diseases, or diseases that affect the ability to breathe. This means that individuals who have any of these diseases are at a higher risk to develop polymyositis.

What are the symptoms for Polymyositis?

Polymyositis is characterized by chronic muscle inflammation and weakness involving the skeletal muscles (those involved with making movements) on both sides of the body. Weakness generally starts in the proximal muscles (those closest to the chest and abdomen, such as muscles of the upper arm and shoulder and the upper leg and hip). The symptoms of polymyositis may continue to worsen from the time the disease presents over a period of weeks or months. The muscle weakness can cause difficulties climbing stairs, rising from a seated position, lifting objects, or reaching overhead. In some cases, the distal muscles (those further away from the chest and abdomen including the lower arms, hands, lower legs, and feet) may also be affected as the disease progresses.  

Other symptoms of polymyositis include arthritis, shortness of breath, difficulty swallowing and speaking, mild joint or muscle tenderness, fatigue, and heart arrhythmias. People with polymyositis may have an increased risk to develop cancer. 

What are the current treatments for Polymyositis?

The treatment of polymyositis is based on the signs and symptoms present in each person. Although there is currently no cure, symptoms of the disease may be managed with the following:
  • Medications such as corticosteroids, corticosteroid-sparing agents, or immunosuppressive drugs
  • Physical therapy to improve muscle strength and flexibility
  • Speech therapy to address difficulties with swallowing and speech
  • Intravenous immunoglobulin: an infusion of healthy antibodies that are given to block damaging autoantibodies that attack the muscle
Mescape Reference offers more specific information regarding the diagnosis and treatment of polymyositis.

What is the outlook (prognosis) for Polymyositis?

The long-term outlook (prognosis) for people affected by polymyositis varies. Most affected people respond well to treatment and regain muscle strength, although a certain degree of muscle weakness may persist in some cases. In most cases, polymyositis is not life-threatening, and many people recover partially or completely from the disease. People who recover from polymyositis after treatment may be at risk of a recurrence of symptoms.

If the treatment for polymyositis is not effective, affected individuals may develop significant disability. In rare cases, people with severe and progressive muscle weakness may develop respiratory failure or pneumonia. Difficulty swallowing may cause weight loss and malnutrition. Individuals with polymyositis may be more likely to develop other autoimmune diseases, cancer, or osteoporosis.

How is Polymyositis diagnosed?

A diagnosis of polymyositis is often suspected in people with proximal muscle weakness and other signs and symptoms associated with the disease. Additional testing can then be ordered to confirm the diagnosis and rule out other diseases that may cause similar features. The testing may include:
  • Blood tests to measure the levels of certain muscle enzymes, such as creatine kinase and aldolase
  • Blood tests to detect specific autoantibodies that cause the autoimmune response associated with polymyositis
  • Electromyography to check the health of the muscles and the nerves that control them
  • Imaging studies such as MRI scan or muscle ultrasound to detect muscle inflammation
  • A muscle biopsy to diagnose muscle abnormalities such as inflammation, damage, or infection

Is Polymyositis an inherited disorder?

Changes (mutations) in a specific gene are not known to cause polymyositis. In general, autoimmune diseases are thought to be caused by a combination of genetic and environmental factors. In some cases, multiple people in the same family may be affected by an autoimmune disease. Therefore, it is possible for people with polymyositis to have other family members affected by the disease or by other autoimmune diseases. 
  • Condition: Rapidly Progressive Interstitial Lung Disease in Pregnant Patient with Anti-Melanoma Differentiation-Associated Gene 5 Antibody-Positive Dermatomyositis
  • Journal: Frontiers in immunology
  • Treatment Used: Combined Immunosuppressant Regimen
  • Number of Patients: 1
  • Published —
This case report describes a pregnant woman with clinically amyopathic dermatomyositis with positive anti-melanoma differentiation-associated gene 5 antibody treated with combined immunosuppressive therapy.
  • Condition: Juvenile Myositis
  • Journal: Current rheumatology reports
  • Treatment Used: Rescue Therapy with Intravenous I mmunoglobulin (IVIG) or Cyclophosphamide
  • Number of Patients: 0
  • Published —
This study presented evidence for the use of intravenous immunoglobulin (IVIG) and cyclophosphamide for juvenile patients with inflammatory myopathies (muscle weakness and rash).