Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathy is a group of rare autoimmune diseases that cause chronic muscle inflammation and weakness, often affecting daily activities like climbing stairs or lifting objects, while also potentially impacting other organs including the skin, lungs, and heart.

Table of contents

• What is Idiopathic Inflammatory Myopathy?
• Types of Idiopathic Inflammatory Myopathy
• Who Gets This Condition?
• What Causes It?
• Symptoms and How It Affects the Body
• How Is It Diagnosed?
• Treatment Options
• Living with Idiopathic Inflammatory Myopathy

inflammatory myopathies, myositis, idiopathic inflammatory myositis

What is Idiopathic Inflammatory Myopathy?

Idiopathic inflammatory myopathy is a group of disorders characterized by inflammation of the muscles used for movement, known as skeletal muscles.^[1] The term “idiopathic” means the specific cause is unknown, “inflammatory” refers to the swelling and irritation in the body, and “myopathy” means disease of the muscle.^[19] When put together, it simply means inflammation of the muscle with an unknown cause.^[19]

These conditions are autoimmune diseases, meaning the body’s immune system mistakenly attacks its own healthy muscle fibers instead of protecting the body from infections.^[7] This attack causes muscle inflammation, which can lead to muscle weakness, fatigue, and difficulty performing everyday activities. The disease is chronic, meaning it lasts for a long time, and can also affect other parts of the body beyond just the muscles.^[3]

Idiopathic inflammatory myopathy is considered a rare disease. The incidence is approximately 2 to 8 cases per million people each year.^[1] The condition can appear at any age, though it usually shows up in adults between ages 40 and 60 or in children between ages 5 and 15.^[1]

Types of Idiopathic Inflammatory Myopathy

There are several different forms of idiopathic inflammatory myopathy, each with unique characteristics and symptoms. The main types include:^[2][5]

• Polymyositis (PM): This type causes muscle weakness, particularly in the muscles closest to the center of the body, such as the hips, thighs, upper arms, and neck. It does not cause skin changes.^[1]
• Dermatomyositis (DM): Similar to polymyositis in terms of muscle weakness, but dermatomyositis is distinguished by a reddish or purplish rash on the eyelids, elbows, knees, or knuckles. Sometimes abnormal calcium deposits can form hard, painful bumps under the skin.^[1] There is also a form called amyopathic dermatomyositis, where patients have the typical rash without muscle weakness.^[3]
• Sporadic Inclusion Body Myositis (sIBM): This form most commonly affects people over age 50 and is the most common type of myopathy in this age group.^[6] The weakness typically affects the wrists, fingers, and front of the thigh. It progresses more slowly than other forms and does not usually respond well to immunosuppressant medications.^[1]
• Antisynthetase Syndrome (ASyS): This type usually presents with a particular combination of symptoms including muscle weakness, arthritis, rough dry skin on the hands called “mechanic’s hands,” lung inflammation known as interstitial lung disease, and color changes in the fingers when exposed to cold called Raynaud’s phenomenon.^[3]
• Immune-Mediated Necrotizing Myopathy (IMNM): Also called necrotizing autoimmune myopathy, this type causes death of muscle cells, leading to muscle weakness that is usually more severe and rapidly progressive than other inflammatory myopathies. It can be associated with the use of cholesterol-lowering medications called statins.^[3][6]
• Overlap Myositis: This occurs when inflammatory myopathy develops in a person who already has another autoimmune connective tissue disease such as lupus, scleroderma, or rheumatoid arthritis.^[3][6]
• Juvenile Myositis: This refers to any type of myositis that occurs in children under age 18. In addition to muscle weakness and skin symptoms, children may have a hoarse voice, stomach aches, and irritability.^[5]

Who Gets This Condition?

Idiopathic inflammatory myopathy can affect people of all ages and races, but certain groups are at higher risk.^[7] Adults are typically diagnosed between ages 40 and 50, while children are usually diagnosed between ages 5 and 10.^[7]

The disease affects women about twice as often as men when it comes to polymyositis and dermatomyositis. However, sporadic inclusion body myositis is more common in men, affecting them about one-and-a-half to two times more than women.^[1][12]

People of predominantly Sub-Saharan African descent are three times more likely to develop myositis compared to people with little or no such ancestry.^[12] It is estimated that approximately 7,000 people are diagnosed with myositis every year in the United States, with upwards of 50,000 people living with the disease.^[12]

What Causes It?

The exact cause of idiopathic inflammatory myopathy is not fully understood. Researchers believe it arises from a combination of genetic and environmental factors.^[1] The term “idiopathic” itself indicates that the specific cause is unknown.

Specific genetic variations may increase a person’s risk of developing the condition. The most commonly associated genes belong to a family called the human leukocyte antigen (HLA) complex. These genes help the immune system distinguish the body’s own proteins from proteins made by foreign invaders such as viruses and bacteria.^[1] Certain variations of HLA genes seem to affect the risk of developing idiopathic inflammatory myopathy.

It is likely that genetic variations increase a person’s susceptibility, and then exposure to certain environmental triggers actually sets off the disorder. Possible environmental triggers that have been identified include infection, exposure to certain medications such as statins or some immunotherapies, and exposure to ultraviolet light such as sunlight.^[1][6] However, most risk factors for this condition remain unknown.

Most cases of idiopathic inflammatory myopathy are sporadic, meaning they occur in people with no family history of the disorder.^[1] However, several people with this condition have had close relatives with other autoimmune disorders, where the immune system malfunctions and attacks the body’s own tissues and organs.^[1]

Symptoms and How It Affects the Body

The primary symptom of idiopathic inflammatory myopathy is muscle weakness, which typically develops gradually over a period of weeks to months or even years.^[1] The weakness often develops slowly and can be subtle at first, affecting a person’s ability to do certain activities.^[12]

Muscle weakness typically affects the muscles closest to the center of the body, such as the muscles of the hips and thighs, upper arms, shoulders, and neck.^[1] People with these forms may find it difficult to climb stairs, get up from a seated position, lift items above their head, or brush their hair.^[1][7] Some patients may trip frequently and be unable to catch themselves or unable to get up from the floor after falling.^[12]

In some cases, muscle weakness may make swallowing or breathing difficult. Sometimes, in the most severe cases, the muscles of the throat or diaphragm can weaken, leading to trouble swallowing or shortness of breath.^[1][12]

Other common symptoms include:

• Joint pain^[1]
• General tiredness or fatigue^[1]
• Unusual rashes, particularly in dermatomyositis^[7]
• Breathing problems^[7]
• Difficulty swallowing^[7]
• Extreme fatigue^[7]
• Muscle pain and tenderness, though this is less common^[7]

The condition can affect the whole body, not just the muscles. Some patients can have arthritis in the hands similar to rheumatoid arthritis, lung inflammation that causes coughing or shortness of breath, and skin inflammation or rashes.^[12] Each patient’s disease experience and mix of symptoms is unique, with some cases being very mild and others severe.^[12]

In dermatomyositis specifically, patients typically have a reddish or purplish rash that affects the back of the hands, chest, back, face, scalp, and sometimes the elbows and sides of the legs. Patients may also notice changes in their cuticles, which can become sore and ragged.^[3]

How Is It Diagnosed?

Diagnosing idiopathic inflammatory myopathy requires a thorough evaluation by a healthcare professional. The diagnosis involves taking a complete medical, family, and lifestyle history, along with performing a comprehensive physical examination to assess muscle strength and look for obvious signs of inflammation.^[6]

Several tests may be ordered to confirm or rule out the diagnosis:

• Blood tests: These detect elevated levels of muscle enzymes such as creatine kinase that may indicate muscle damage and inflammation. Blood tests can also detect specific antibodies called myositis-specific autoantibodies that help identify the type of myositis.^[3][6]
• Muscle biopsy: A small piece of muscle tissue is examined under a microscope to look for characteristic changes that indicate inflammation and damage. This is often considered essential for accurate diagnosis.^[7]
• Electromyography (EMG): This test measures the electrical activity in muscles to help identify muscle disease.^[7]
• Magnetic resonance imaging (MRI): MRI scans can look for muscle inflammation and damage without requiring an invasive procedure.^[7][6]

Because certain subtypes of idiopathic inflammatory myopathy are associated with cancer occurrence, especially during the three years before and after diagnosis, tests to rule out cancer may be needed.^[7][9]

A rheumatologist, a doctor who specializes in diseases of the joints and muscles, typically manages the diagnosis and treatment of idiopathic inflammatory myopathy.^[7]

Treatment Options

While there is no cure for idiopathic inflammatory myopathy, there are various treatments available to manage symptoms, prevent disease progression, and improve quality of life. The cornerstone of therapy for most types (except inclusion body myositis) is treatment with medications that suppress the immune system.^[8]

The first treatment for inflammatory myopathies is usually an oral corticosteroid, such as prednisone, at a high dose. Muscle enzymes typically return to normal within 4 to 6 weeks, and strength returns in 2 to 3 months.^[7] However, long-term use of corticosteroids can cause significant side effects.

To allow for lower doses of corticosteroids and achieve better long-term disease control, doctors may add other drugs to the treatment plan, including:^[7]

• Methotrexate
• Azathioprine
• Mycophenolate mofetil (CellCept)
• Cyclosporine (Neoral, Sandimmune)
• Tacrolimus (Prograf)

Some patients with severe disease may need intravenous immunoglobulin (IVIG), which is an effective treatment that can be considered in patients with difficult-to-treat disease.^[7][9] Another medication called rituximab (Rituxan) may also be used in some cases.^[7]

Unfortunately, no effective medical treatment for sporadic inclusion body myositis is currently available.^[9] For this type, treatment focuses on managing symptoms and maintaining function through physical therapy and exercise.

Physical therapy and exercise are important parts of standard myositis treatment plans for all types. Physical exercise has been shown to reduce inflammation and fatigue and increase aerobic capacity, stamina, and muscle strength, even in people with myositis.^[18] Regular physical activity can improve quality of life and reduce the risk of serious chronic diseases such as type 2 diabetes, osteoporosis, high blood pressure, and cardiovascular disease.^[18]

Specialist multidisciplinary team involvement is essential for optimal patient outcomes, as the disease can affect multiple organ systems.^[9]

Living with Idiopathic Inflammatory Myopathy

Living with idiopathic inflammatory myopathy can significantly impact quality of life, but there are many ways to manage the condition and maintain the best possible health.

Good health habits are important for long-term management. These include eating a healthy, well-balanced diet, getting regular exercise, and staying at a healthy weight.^[7] It is advisable to avoid becoming overweight, not smoke, and avoid alcohol, as alcohol is a muscle toxin.^[17]

People with dermatomyositis should use sun protection to prevent rashes from worsening. This means limiting time outdoors and using sunscreen when going outside.^[7]

If trouble swallowing occurs, it helps to eat soft foods or puree solid foods in a blender. To prevent choking, sitting up in bed to eat is important.^[7]

Once past the most acute and critical phase of the disease, physiotherapy is recommended for all patients.^[17] It is advisable to perform aerobic exercise without becoming overexerted and, if possible, to do this in a swimming pool to avoid injury.^[17] Exercise is currently the only treatment recommendation for those with inclusion body myositis.^[18]

Treatment with bisphosphonates, calcium, and vitamin D is highly recommended for all patients, particularly post-menopausal women, because of the high risk of bone fractures related to both the disease and corticosteroid treatment.^[17]

Some patients require psychological support to help them accept the illness and adapt to daily life with a chronic condition.^[17] People with myopathy may look healthy and normal on the outside, so it is important for employers, teachers, and family members to understand the limitations that muscle weakness causes.^[7]

When traveling for any length of time, it is important to carry an updated medical report showing the diagnosis and progression of the illness, have all medications on hand, and know the location of a reference hospital in case assistance is needed.^[17]