What Is Myositis?

Overview

Throughout this article, we will explore Myositis to help provide you with a clear understanding of this group of inflammatory muscle diseases. We will explore myositis, any underlying causes, symptoms, and available treatment options to ensure that you are well-informed on myositis and gain valuable insight to aid you in making informed decisions about your muscle health. 

Myositis refers to a group of inflammatory muscle diseases which can be identified by inflammation and weakening of the skeletal muscles.¹ There are several different types of myositis, including inclusion body myositis, polymyositis, dermatomyositis and juvenile myositis, each with its distinct features and symptoms. The most common symptoms of myositis include fatigue, weakness, difficulties performing everyday tasks and muscle pain. Timely diagnosis and effective treatment methods are essential in improving the quality of life of those individuals affected by this disease and aid in preventing further complications. 

If you’re interested in learning more about myositis, there is much more to explore throughout this article, from different subtypes and their characteristics to the potential causes and available treatment methods. Throughout this article, we aim to provide further insights to enhance your understanding of myositis so you can make an informed decision regarding the management and treatment of this disease. 

Outline 

Introduction

1.  Definition of myositis

Myositis is a group of rare inflammatory muscle diseases which can be characterised as weakening and inflammation of the skeletal muscles. There are several different types of this condition, each with its own distinct clinical and pathological symptoms; these types include inclusion body myositis, polymyositis and dermatomyositis.¹ As mentioned before, early diagnosis and treatment are key in managing this condition and preventing further complications.

2.  Prevalence and affected populations

The prevalence of myositis is relatively low, affecting approximately 5-10 individuals per 100,000 population.² While this condition can affect individuals of any age, it most commonly affects adults between 30 and 60 years old, with slightly higher incidences recorded in females.³ Specific types of myositis, for example, dermatomyositis, are more prevalent in older adults and children. Myositis can affect individuals from all ethnic backgrounds; however, higher incidences have been recorded in individuals from certain Hispanic and black ethnic groups.⁴  

Types of myositis

1.  Polymyositis

Polymyositis is one of the most common types of myositis, which can be identified by chronic weakness and inflammation in different skeletal muscles. This autoimmune disease (when your body's immune system can’t tell the difference between your cells and foreign cells, causing your body to attack your cells) commonly affects the proximal muscles - muscles which are located closer to the core of the body. This can lead to difficulties in mobility as well as making it harder to complete everyday activities. To diagnose polymyositis, a clinical evaluation will be performed, including blood tests and muscle biopsies. Early treatment using immunosuppressive medication helps to manage symptoms and greatly improves the quality of life for individuals with polymyositis.⁵

2.  Dermatomyositis

Another type of myositis is dermatomyositis; as it can be understood from the name, it is identified by muscle inflammation alongside a skin rash. This autoimmune condition affects not only the muscles but also the skin, leading to changes in the skin, such as a purple or reddish rash which can be seen on the knuckles, chest and face. Similarly to polymyositis, this condition affects the muscles close to the core of the body. To diagnose dermatomyositis, a clinical evaluation will be performed, including blood tests and muscle and skin biopsies. Patients affected by this condition are given immunosuppressive medication (such as methotrexate and azathioprine) to help manage symptoms and prevent further complications.⁶

3.  Inclusion body myositis

Inclusion body myositis (IBM) is distinct from other forms; it affects older individuals (over 40) and progresses slowly over time. IBM can be identified by muscle weakness and atrophy that slowly progresses over time. “Inclusion body” refers to a particular characteristic of this disease where abnormal protein deposits are found within the muscle cells. In terms of treatment, IBM is very challenging to treat, unlike other types of myositis, as it displays resistance to immunosuppressive medication; as a result, current treatment focuses on relieving symptoms and maintaining independence for those affected.⁷  

4.  Juvenile myositis

The rarest form of myositis is known as juvenile myositis, which specifically only affects adolescents and children. There are two types of juvenile myositis known as juvenile polymyositis (JPM) and juvenile dermatomyositis (JDM). JPM causes muscle weakness, whereas JDM causes muscle inflammation along with skin rashes. Current treatment for this condition mainly involves immunosuppressive medication, as well as physical therapy, to prevent further complications and improve long-term outcomes for young patients.⁸

Causes and risk factors

1.  Autoimmune factors

A key cause in developing myositis is autoimmune factors this is where the immune system mistakenly attacks the muscles within the body, causing damage and inflammation. Whilst the exact causes of this autoimmune response are not known, it has been suggested that environmental factors and genetic predisposition may contribute. It has also been suggested that other autoimmune diseases, such as rheumatoid arthritis and lupus, may increase the risk of developing myositis.⁹

2. Genetic predisposition

An additional cause of developing myositis is genetic predisposition. Whilst the exact genes that increase an individual’s chance of developing myositis are not known, studies suggest that a family history of myositis can increase the risk of developing this disease.⁹ Understanding how genetic predisposition can impact the development of myositis can help detect the disease early, allowing for effective treatment outcomes in those at higher risk. 

3.  Environmental triggers

It has been suggested that environmental triggers play a key role in developing myositis. These triggers can vary greatly and include exposure to specific medications, infections or additional external factors. Infections could potentially activate the immune system,, resulting in an autoimmune response that targets the muscles in certain individuals.¹ In addition, specific drugs have been identified with myositis as being a potential side effect.¹

Symptoms

1. Muscle weakness and fatigue

The main symptom of myositis is muscle weakness and fatigue. Individuals affected by myositis may experience sudden or gradual weakening of the muscles that are close to the core of the body (such as the shoulders, hips and thighs)². Affected individuals with myositis find that activities which require physical effort, such as lifting objects or even climbing stairs, become particularly challenging as the disease actively affects the muscles used in these situations. In severe cases, individuals may experience exhaustion even after minimal physical effort.

2. Muscle pain and tenderness

A common symptom associated with myositis is muscle pain and tenderness. Individuals affected by this disease experience discomfort and pain in affected muscles, which can potentially worsen with physical activity or movement. Additionally, affected individuals may experience tenderness in the muscles, which can make them sensitive to touch.² This pain and tenderness experienced can vary in distribution and intensity. 

3. Skin rashes (in dermatomyositis)

Dermatomyositis is a type of myositis where, alongside muscle inflammation, affected individuals also experience skin rashes. These skin rashes can appear in different forms across the body, such as purple or reddish rashes on the knuckles, back, neck, face, and chest. These rashes may be extremely itchy and can also be sensitive to sunlight.⁶

4.  Difficulty swallowing (in inclusion-body myositis)

A main symptom that indicates inclusion body myositis is difficulty swallowing, otherwise known as dysphagia. In this type of myositis, the muscles that are responsible for swallowing (the oesophagal and pharyngeal muscles) are affected. This creates challenges in moving liquid and food from the mouth and stomach. As a result, there is an increased risk of malnutrition and choking. Treatment methods to help maintain proper hydration and nutrition for individuals with IBM involve speech therapy, swallowing exercises, and changes in diet.¹⁰

If you are experiencing any of these symptoms, you should consult your GP to help alleviate any discomfort. 

Treatment

1. Medications (corticosteroids, immunosuppressants)

One of the main treatment options for myositis involves medications such as immunosuppressants and corticosteroids. Corticosteroids are prescribed to help alleviate symptoms and reduce muscle inflammation, whereas immunosuppressants are prescribed to suppress the immune system and control the autoimmune response that is responsible for myositis.¹¹ These medications help to manage this disease as well as improve muscle strength; however, due to potential side effects, close monitoring by healthcare professionals is required to minimise any potential risks.  

2. Physical therapy

Alongside medication, physical therapy is the main treatment option for patients with myositis. A physical therapist will work with an individual on therapeutic techniques and structured exercises to aim at improving muscle flexibility, strength, and function. Physical therapy is often a tailored programme taking into account the individual's specific abilities and needs, whether that be reducing muscle pain, regaining or maintaining mobility or improving their overall quality of life.11 Regular and long-term physical therapy sessions are vital in the management and overall well-being of individuals with myositis, and they can even prevent complications related to muscle weakness.

3. Occupational therapy

Occupational therapy focuses on helping individuals with myositis cope and adapt to the challenges associated with muscle weakness and additional symptoms that may impact their daily routines. The occupational therapist will work together with patients to create personalised strategies that can range from encouraging independence to assisting with everyday activities such as cooking, cleaning, dressing and improving mobility.¹² Implementing strategies to help with the practical aspects of daily living can greatly enhance the overall quality of life for individuals with myositis. 

Summary

Myositis is a group of diseases that can be identified by muscle weakness and inflammation. There are various types of myositis, including dermatomyositis, polymyositis, inclusion body myositis and juvenile myositis. The key causes associated with myositis are genetic predisposition and autoimmune factors; there is also overwhelming evidence that environmental triggers may be associated with developing myositis. Timely diagnosis and effective treatment methods, such as physical therapy, medication, and supportive care, are vital in not only managing symptoms but also improving the overall well-being of individuals affected by this condition.