Juvenile Polymyositis (JPM) is a rare autoimmune condition that affects children under the age of 18. Breaking down the term in medical language, the word “myo” means muscle, “itis” indicates inflammation, and “poly” means multiple. Therefore, polymyositis is a condition that involves the inflammation of multiple muscles in the body.

Since it is such a rare condition, much aboutthis disorder is not fully understood. It does not have a specific cause or cure, but fortunately, there are various ways we can manage the symptoms associated with this disorder. JPM can significantly impact someone's life, so finding ways to manage the symptoms, as early on as possible, is essential. 

Understanding JPM

To help your loved ones suffering from this disorder, it is essential to fully understand this disorder and its complications. 

JPM rarely affects children but is mostly diagnosed in early adolescence (10-13 years) and it is slightly more prevalent in girls. It is estimated to roughly affect two to four children per million,¹ which is quite a low prevalence. The fatality rate ofJPM has decreased significantly over the years, due to better medication available to manage the symptoms. 

Since it is an autoimmune condition, this means that the body's immune system mistakenly recognises healthy cells and tissue as foreign particlesand attacks them. While the exact cause is not known for sure, it has been hypothesised that there mightbe a genetic component involved. It is possible that this autoimmune reaction which causes JMP only occurs in people who are already genetically susceptible to it and are exposed to certain environmental triggers such as the exposure to tobacco smoke or air pollutants during the prenatal period.² (which is the period during pregnancy, before birth), or exposure to microbes which can trigger an exaggerated immune response. You might have a higher chance of developing JPM if you have a family history of autoimmune diseases. 

In JPM, the muscles are primarily affected and are attacked by the immune system, leading to inflammation. This inflammation gradually leads to muscle weakness, which causes the symptoms of this disease. Severe forms of JPM, or cases left untreated, can eventually start to affect muscles of the digestive system, heart, and lungs which can lead to breathing difficulties. 

Clinical manifestations 

Some of the common symptoms associated with JPM are:

• A gradual weakness involving the shoulders, arms, neck, hips, and thighs. This weakness affects both sides of the body equally and progresses slowly 
• Difficulty with simple everyday movements such as getting out of bed, climbing stairs, getting dressed, etc
• General fatigue and tiredness
• Joint pain/muscle pain
• Fever
• Stiff joints which may cause shortening and permanent bending of joints (contractures)
• Digestive problems such as trouble swallowing, coughing whilst eating, heartburn, pain, gastroparesis, chronic diarrhoea or constipation, or changes inthe voice
• Shortness of breath and difficulty breathing, in severe cases

At times, there are also skin symptoms when the skin is involved in the disorder. Typically, there are no skin symptoms in JPM, hence, when there is an involvement of the skin along with the muscles, it is known as dermatomyositis. Some skin symptoms can be seen as:

• A purple-ish rash around the eyes, known as the heliotrope rash³
• Bumps over the elbows, knees, and knuckles, known as Gottron's sign
• Hard, painful lumps of calcium under the skin

Diagnostic approach

The process of diagnosing any type of myositis, including JPM, can be challenging. This is because these disorders are so rare, they might not be at the top of the differential diagnosis list. In addition, symptoms vary in each patient and often the symptoms can be quite similar to those experienced in autoimmune diseases. There are also many different forms of myositis which can make it more difficult to diagnose and classify. 

However, there are some general steps for diagnosis that your doctor will follow: 

• There will be an initial physical exam to check for muscle weakness and/or skin rashes on the body. Your doctor will also take a detailed medical history of your symptoms as well as a detailed family history
• There will be blood tests to check the levels of muscle enzymes in the blood. These include creatine kinase (CK), aldolase, aspartate aminotransferase (AST), alanine aminotransferase (ALT), aldolase, and lactate dehydrogenase (LDH). IN JPM, the muscles are damaged, which causes leakage of muscle enzymes into the blood and elevation of muscle enzymes⁴
• Since it is an autoimmune disease, the body attacks healthy tissue and produces antibodies against them. These antibodies are called Antinuclear antibodies (ANA) and their levels can be analysed in a simple blood test
• Magnetic Resonance Imaging (MRI) is done to see the extent of the muscle inflammation and damage
• Electromyography (EMG) is performed during which the muscles undergo nerve stimulation, and the electrical activity or muscle response is measured and recorded
• To finalise the diagnosis, a muscle biopsy is performed. In this procedure, a small sample of muscle tissue is obtained and examined under a microscope

Treatment strategies 

Unfortunately, there is no known cure to JPM but there are several strategies available to manage and contain this disorder. Treatment strategies aim to put the disorder into remission, treat any complications, and relieve the symptoms. One or more drugs may be required to reach remission, and the medications are continued for a while to maintain remission. At times, the medications can be slowly tapered off whilst maintaining the remission. 

Some standard treatments might be as follows:

• Initially, corticosteroids are given to repress the immune system, as it is attacking the healthy muscle cells. After the immune system has been adequately repressed, corticosteroids can be tapered off and methotrexate can be given as a long-term maintenance medication
• At times, corticosteroids might not be able to suppress the immune system or maintain remission, so additional medication might be considered. One of these medications is an intravenous immunoglobulin (IVIg). These are antibodies that are collected from the blood of a healthy donor and then given to the recipient via a needle, directly into a vein. These healthy antibodies can bind to and help remove the antibodies in the recipient's blood that are attacking healthy muscle tissue
• Similarly, there is a man-made antibody, known as Rituxan, that can help in JPM by temporarily stopping the production of the antibodies that are destroying healthy muscle cells⁵
• Another medication that is used in JPM to suppress the immune system is cyclophosphamide. It is also used as a chemotherapeutic agent to treat various cancers. It is usually only given for severe cases of JPM or cases unresponsive to the above medications
• Physical therapy is also an important part of managing JPM. It can help to improve muscle strength and motility and even help in reducing muscle inflammation. It can also enable the patient to perform various everyday tasks by themselves, as they slowly recover from their muscle weakness⁶

Prognosis and complications

Various long-term complications could develop as a result of JPM. If the muscles of the heart or lungs become involved, it could lead to breathing difficulties or various heart diseases. If the muscles of the gastrointestinal system become involved, it could lead to swallowing difficulties and malabsorption which can further cause weight loss and malnutrition. 

Furthermore, contractures (muscle tightening) could form in the muscles or tendons. These produce a tightening that can lead to loss of normal movement and motility, especially if a contracture develops in the legs. 

However, the long-term prognosis of JMP is not dire and most patients have a favourable outcome.⁷ Mild disability is common but extreme disability in children with JPM is rare. Early diagnosis and treatment to stop the disease progression is integral in limiting disability and other complications. 

Summary

JPM is an autoimmune disease and it is very rarely seen. It is a childhood disorder, as indicated by the name. The exact cause is unknown but there is some evidence to suggest that there might be a genetic factor as well as a prenatal environmental trigger such as tobacco smoke. 

In JPM the antibodies mistakenly attack healthy muscle cells which leads to inflammation in the muscles. Eventually, the damage results in muscle weakness and pain which can manifest as difficulty in carrying out normal daily activities and pain in the muscles. If the skin is also involved, the condition is known as dermatomyositis. Severe forms of JPM or untreated JPM can lead to serious complications of the heart, lung, or gastrointestinal muscles. 

There is so far no known cure for JPM, but management aims to obtain remission and prevent complications. This is done with the help of various medications which can help to suppress the immune system but it is also important to have regular physical therapy. Physical therapy can improve muscle weakness and motility. 

JPM does not have a poor prognosis and even though it is scary to be diagnosed or have a loved one diagnosed with a long-term health condition, there is a lot of help and support available, as well as various ways to manage it.