Polymyositis is a rare inflammatory disease that involves muscle inflammation and weakness. It tends to affect muscles close to the trunk of the body and affects then eventually other muscles. It can make many basic movements difficult, and generally presents itself in adulthood; between the ages of 30 and 60. It is part of a group of diseases called myopathies, which directly affect the muscles.

It is thought to be caused by an autoimmune reaction; where the immune system begins to attack the body mistakenly, with some level of genetic factor being thought to contribute. Although there is no known exact cause of Polymyositis.

With no known cause, it is important to know the symptoms that may arise with polymyositis; as this can signal the need for treatment, these symptoms may include muscle weakness and pain, joint stiffness and pain with many other potential symptoms. Treatment can help ease symptoms; as there is no cure left; untreated polymyositis can lead to issues with breathing and swallowing and seriously affect quality of life.

Causes of polymyositis

Autoimmune factors

Being an autoimmune disorder, this occurs when the immune system begins to attack muscle cells in the body, but it is unclear what exactly may trigger the initial autoimmune response.

Although not known to be a direct cause it is thought that a person can have a genetic predisposition to developing Polymyositis, as genetics can alter the effectiveness of the immune system.¹ 

Environmental triggers

Environmental triggers are external factors that can cause an autoimmune response leading to the immune dysfunction that attacks muscle cells.

Viruses are environmental triggers that can cause Polymyositis, the common viruses that can cause this response are:

• Human immunodeficiency virus (HIV)
• HTLV1
• Hepatitis C

The presence of these viruses in the body can cause the immune system to fail, attack the muscle cells mistakenly, and lead to the symptoms of Polymyositis.

Medication and other drugs can cause the autoimmune response that causes the further development of Polymyositis and the symptoms. Some of these drugs are as follows:

• Interferon-Alpha (treats cancer and hepatitis)
• Carbimazole (treats thyroid disease)
• Phenytoin (treats seizures)
• Angiotensin-converting enzyme (ACE) inhibitors (treat high blood pressure)

All these have been found as causes of the autoimmune response that is associated with Polymyositis.^1,.²

Symptoms of polymyositis

• Muscle weakness- particularly the muscles closest to the trunk.
• Muscle pain and stiffness
• Joint pain and stiffness
• Trouble breathing
• Issues swallowing

These symptoms; particularly muscle weakness, can lead to issues while performing everyday actions. Those suffering with Polymyositis often have trouble standing from a seated position, climbing stairs and lifting objects.³ 

Related conditions

Raynaud's Phenomenon- A person's extremities will turn pale when initially exposed to colder temperatures.

Connective Tissue disorders- Polymyositis affects connective tissue and can occur in tandem with other diseases that affect other connective tissue such as: Rheumatoid Arthritis and Lupus.

Cardiovascular Disease- Inflammation of the heart muscles can cause other complications in polymyositis patients, like cardiac arrhythmias or congestive heart failure.

Lung DIsease- Interstitial lung disease can develop in conjunction with Polymyositis, which causes scarring of the lungs and reduces their ability to move and inflate whilst breathing.

Cancer- There is an elevated risk of cancer for those who suffer from Polymyositis.

These conditions are not direct complications of Polymyositis; but are diseases often associated with it, and may cause further issues as the disease progresses.⁴

Diagnosing polymyositis

To diagnose Polymyositis a doctor considers an individual's medical history; as well as family history, and a physical examination. This can then be confirmed with a battery of tests.

The physical examination helps the doctor determine if the person is suffering from muscle weakness that is characteristic of Polymyositis.

Blood tests

Blood tests are performed to assess the level of creatine kinase (CK) in the blood, as it rises in polymyositis patients. (CK is an enzyme that is released from damaged muscle fibres, so is at higher levels in those with polymyositis as muscle inflammation and damage are also increased). Other blood tests can look for specific antibodies and inflammatory mediators; these are important in the immune process but are overly active in autoimmune conditions, it is reported that there is a significant increase in certain proinflammatory proteins in the blood.²

Electrical tests

Electromyography (EMG) tests the electrical activity of a muscle at rest and when contracted, nerve conduction tests are similar and test the speed of nerve conduction and the strength of a nerve impulse. These tests can be used in a diagnosis as in those with Polymyositis results would be abnormal.

These tests can also help rule out other disorders that have similar symptoms to Polymyositis.¹

Muscle biopsy

A small amount of muscle tissue is removed surgically, this can then be inspected to confirm the presence of inflammation that is characteristic of Polymyositis.⁵

Imaging

Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) can be used by doctors to find the exact area of muscle that has been damaged by Polymyositis.² 

Treatment

Corticosteroids- Corticosteroids, such as prednisone, are medications that are anti-inflammatory, to reduce the symptoms, these may be needed long-term to manage the disease.

Immunosuppressive Drugs- These drugs reduce the function of the immune system, this is required to suppress the immune system's attack on the muscle, as it is a malfunction of the immune system.

Intravenous Immunoglobulin (IVIg)- IVIg contains healthy antibodies that block the body's dysfunctional antibodies from attacking the muscle fibres. This is infused into the blood in the hope of reducing inflammation, this may need to be repeated for continued benefits.⁶

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Physical Therapy- Stretching and exercising can strengthen and maintain muscles to counter the damage and weakness that occur as part of Polymyositis.

Prognosis

Being incurable, Polymyositis continues to progress for the patient’s entire life. This can lead to complications as the muscles gradually become weaker and weaker; as muscles in the digestive tract and chest are affected breathing and the ability to swallow. This can result in malnutrition; due to an inability to eat, and respiratory failure attributed to lessened ability to breathe. Severe Polymyositis can lead to disability, and require intervention in eating and breathing.

As Polymyositis can affect any muscle tissue there is potential for involvement of the heart muscle, inflammation here can cause further cardiac issues, and myocarditis (inflammation of the heart) can then lead to more serious heart issues such as arrhythmias or congestive heart failure.

Summary

Polymyositis is an autoimmune disease that is characterised by muscle weakness and inflammation. The body's own immune system begins to attack the muscle fibres, causing a person suffering from Polymyositis to have difficulty with even basic tasks such as lifting objects, climbing stairs and standing up from a seated position.

There is no known specific cause, but it is thought that it can be triggered by a virus that sets in motion an aggressive immune response, or certain medications. There are thought to be some genetic factors that determine whether someone is at a greater risk of having the autoimmune response triggered.

Diagnosis requires a doctor to conduct physical tests to look for the characteristic muscle weakness. The diagnosis can then be confirmed with blood tests, electrical muscle and nerve tests and muscle biopsy.

Polymyositis is incurable, treatment involves managing the symptoms, this involves the use of anti-inflammatory drugs, immunosuppressive drugs, IVIg and physical therapy.