Inclusion Body Myositis

Inclusion body myositis is a slowly progressive muscle disease that most commonly affects people over 45, causing gradual weakness in the limbs and fingers. While there is currently no cure, understanding this condition and staying active can help maintain quality of life.

Table of contents

• What is Inclusion Body Myositis?
• Signs and Symptoms
• Causes and Risk Factors
• Diagnosis
• Treatment and Management
• Living With Inclusion Body Myositis

What is Inclusion Body Myositis?

Inclusion body myositis, often abbreviated as IBM, is a degenerative muscle disease that causes gradual and painless weakening of the muscles^[1]. The term “inclusion body” refers to abnormal clumps of proteins that gather inside muscle cells, contributing to their weakening^[1].

IBM is the most common acquired muscle disease in people over the age of 45^[3]. It is also one of the most prevalent myopathies — diseases that attack and weaken muscle fibers^[1]. Research suggests IBM may affect between 5 and 9 out of every 1 million adults, though the exact number is unknown^[1][2].

The disease is more common in men than in women, occurring nearly twice as frequently in males^[12]. Some sources report the male-to-female ratio as approximately 3:1^[1].

IBM is distinct from other forms of myositis because of the presence of abnormal protein deposits called inclusion bodies, which can be seen during a muscle biopsy^[2]. The disease belongs to a group of conditions called the idiopathic inflammatory myopathies, which involve inflammation of the muscles or associated tissues^[2].

Signs and Symptoms

Symptoms of IBM usually appear after the age of 50, although the disease can occur earlier^[4]. The muscle weakness from IBM develops gradually and usually begins in the limbs^[1]. For many people, it is not uncommon to realize that they had been experiencing symptoms for many years before they were diagnosed^[3].

Unlike other forms of myositis, weakness in IBM typically has an asymmetric distribution, meaning one side of the body may be more affected than the other^[3]. The disease most commonly presents with weakness predominantly affecting the muscles that flex the fingers and the muscles that extend the knees^[12].

Some of the first signs people notice include frequent falls, difficulty getting up from a chair, and weakened grip^[3]. You might start having trouble pinching and grasping objects, or notice that you’ve started tripping and falling a lot^[1]. Some people notice a lack of dexterity when they try to button their shirts or write with pens^[1].

Common symptoms of IBM include^[3][1]:

• Frequent falls
• Difficulty walking or climbing stairs
• Trouble standing from a seated position
• A foot that seems to drop when walking, causing tripping
• Weakened hand grip and difficulty flexing the fingers
• Difficulty writing, manipulating keys, and other activities requiring finger control
• Weakness and noticeable shrinking of the quadriceps (main muscle of the thighs)
• Weakness in the forearm muscles
• Visible muscle atrophy (thinning and wasting of muscles)
• Mild, frequent muscle pain

Many people with IBM notice shrinking in the forearms and thighs as the muscles become weaker^[3]. As symptoms progress, muscle weakness may affect the neck or esophagus, causing difficulties lifting the head or swallowing^[1].

Trouble swallowing, called dysphagia, is also a common problem for those with IBM, and in rare cases may be the first symptom^[3]. Up to half of people with IBM develop swallowing difficulties^[1][4].

Causes and Risk Factors

Inclusion body myositis is idiopathic, which means that it appears to happen spontaneously, and researchers don’t fully understand what causes it^[1]. The cause of IBM is unclear and likely involves multiple factors^[2].

As with other types of myositis, chronic inflammation in the muscles contributes to weakening them. However, researchers don’t know what causes the inflammation^[1]. It might be a type of autoimmune disease, where the body’s immune system turns against its own muscles and damages muscle tissue^[1][8].

Inclusion bodies also play a part in IBM. These are clumps of abnormal proteins within muscle cells that may be byproducts of a viral infection, cellular damage, or genetic mutations^[1]. Inclusion bodies often occur in neurodegenerative diseases and may interfere with how cells function^[1].

There is currently some debate among experts about whether or not IBM is actually an inflammatory disease. Inflammatory cells are present in muscle tissue from those with IBM, especially earlier in the disease process, but their role in causing muscle weakness is unclear^[3]. What sets IBM apart is the presence of abnormal protein accumulations and tiny empty spaces called vacuoles within the muscle fibers, reflecting a degenerative component of muscle damage^[3].

IBM is usually a sporadic disorder, meaning it occurs randomly and is not inherited. However, a few cases of hereditary inclusion body myopathies exist, which should not be mistaken for inclusion body myositis^[3][8].

Diagnosis

Diagnosing IBM can be challenging because its symptoms may resemble many other related conditions, including polymyositis and myasthenia gravis^[1]. There is not a single test that identifies IBM; the diagnosis is based on a combination of information and tests^[7].

To diagnose IBM, a healthcare provider will begin by reviewing your symptoms and examining your muscles^[1]. Your doctor will ask for a complete medical history and will perform a thorough physical examination^[7]. The provider will look for distinguishing features, such as which muscles are affected, whether one side is more affected than the other, whether you have visible muscle wasting, and your age when symptoms began^[1].

Several tests may be performed to help with diagnosis^[1][7]:

• Creatine kinase (CK) test: A blood test that measures levels of a certain enzyme. Elevated levels can indicate muscle damage.
• Blood tests to screen for viruses and various autoimmune markers
• Nerve conduction studies and electromyography (EMG): Tests that evaluate the electrical activity of muscles and nerves
• Muscle MRI studies to visualize muscle damage
• Muscle biopsy: The most specific test for the diagnosis of IBM. A small piece of muscle is removed, usually from a thigh muscle or the biceps muscle, and examined under a microscope. A muscle biopsy remains a critical diagnostic test to determine whether you have inclusion body myositis^[7].

Diagnostic criteria for IBM include mandatory features such as age of onset later than 45 years, duration of symptoms more than 12 months, and serum creatine kinase level not more than 15 times the upper limit of normal^[8]. Clinical features that support diagnosis include weakness of the quadriceps more than hip flexors and weakness of finger flexors more than shoulder muscles^[8].

Treatment and Management

There is currently no cure for inclusion body myositis^[4][11]. No definitive treatment has been proven effective for IBM, and the disease is generally unresponsive to most therapies^[4][13].

Unfortunately, many patients with IBM do not respond to medications that suppress the immune system^[7]. Early studies of various immunosuppressive or immunomodulatory therapies, including steroids, methotrexate, azathioprine, cyclophosphamide, and intravenous immunoglobulin, have been largely disappointing^[13]. Immunosuppressive steroid therapy, which is used to treat most idiopathic inflammatory myopathies, is typically ineffective in people with sporadic IBM and is not recommended in most cases^[11].

Various clinical trials targeting inflammatory and some of the noninflammatory pathways have failed^[12]. Some medications that have been studied or are currently being studied include arimoclomol, bimagrumab, rapamycin, and ulviprubart, though none have yet been proven definitively effective^[10].

Disease management is focused on optimizing muscle strength and function using strategies such as exercise, physical therapy, occupational therapy, and speech therapy^[11]. The mainstay of therapy is physical and occupational therapy, and in individuals with swallowing difficulties, speech and language therapy^[7].

People with IBM who are experiencing difficulty swallowing should be evaluated by a speech therapist, who can help with techniques to minimize the risk of aspiration (blocking of the airway by food or fluid)^[11]. Close monitoring of swallowing and respiratory function is important^[12].

Physical therapy may be helpful in maintaining mobility^[4]. Treatment plans are typically individualized to meet the needs of the affected person, and ongoing monitoring is required to optimize the treatment protocol^[11].

Living With Inclusion Body Myositis

IBM progresses over several years. It isn’t life-threatening, but it can become disabling over time^[1]. The disease progresses at different rates and with different symptoms in each person, but does not typically affect life expectancy^[2]. However, IBM is associated with increased morbidity and mortality^[12].

People with IBM may experience persistent symptoms that require constant management over the course of a lifetime^[2]. While there aren’t many medications available for patients with IBM, the best way to improve mobility and maintain muscle longevity is to exercise and stay active^[15].

Practical tips for living with IBM include^[14]:

1. Continue your normal routine as best you can, doing the things you love or need to do as long as possible
2. Exercise regularly without compromising safety — work out with light weights, ride a stationary bike, take a daily walk, or swim
3. Keep your brain engaged by reading, staying involved in work or business, or taking classes
4. Stay involved socially with family, friends, neighbors, clubs, or volunteer activities
5. Focus on the positive aspects of life
6. Keep a journal to document your daily condition, attitude, and mental and emotional status
7. Help family and closest friends understand how the disease affects you so they better understand your needs
8. When the risk outweighs the benefits, it’s time to rethink your approach and consider mobility aids or other assistive devices

Adapting an exercise routine and addressing mobility issues are important parts of management^[12]. Exercise has been shown to help preserve muscle strength in people with IBM^[11]. However, it’s important to balance activity with rest and to use appropriate safety measures to prevent falls and injuries^[14].