Inclusion body myositis (IBM)

Inclusion body myositis (IBM) is a progressive condition which causes muscle inflammation and results in muscle weakness and wasting. It first affects the thigh muscles, which help straighten the knees, and the forearm muscles, which help bend the fingers. Other symptoms may include swallowing difficulties. Symptoms of IBM usually start in people aged over 50. IBM does not affect the skin, heart, eyes, gut, or bladder.

IBM is a type of myositis – a group of conditions that cause muscle inflammation and weakness. These conditions are also known as idiopathic inflammatory myopathies. IBM differs from other types of myositis as it doesn’t respond well to immunosuppressive treatments like steroids.

Muscle weakness

Muscle weakness in IBM typically begins in people over 50 years old and progresses slowly. The most frequently affected muscles are the thigh muscles (quadriceps more than hamstrings) and the forearm muscles. The muscles are often affected in an asymmetrical way, so one side of the body may be weaker than the other.

Weakness in the thigh muscles, which help straighten the knee, can lead to challenges climbing stairs and getting up from a chair. Falls can happen because the weakened quadriceps muscles make it difficult for people to ‘lock’ their knees, which means they can give way unexpectedly. Weakness in the muscles that control the ankle can cause difficulty lifting the foot, a condition called foot drop, which also increases the risk of falling. It can also be hard to get up without help after falling.

Weakness in the forearms can make it difficult to flex the wrists or fingers. This makes it difficult to perform tasks that require fine motor skills, such as gripping objects, turning keys, and buttoning shirts.

Swallowing

The muscles used for swallowing may also be affected, making it hard to swallow food or liquids (dysphagia). This can cause symptoms such as coughing and choking while eating or drinking. It can also cause a feeling that food is stuck in the throat. Speech and the ability to chew are usually not affected. If swallowing problems aren’t managed, they can cause aspiration (food, drink, or saliva going into the lungs, causing inflammation and infection), unplanned weight loss, malnutrition, and dehydration.

Respiratory

People with IBM can have some weakness in muscles used for breathing. This should be monitored but doesn’t usually require medical intervention. People may also have a weak cough and be more likely to get chest infections.

The cause of IBM is unclear. Muscle inflammation happens and is believed to be linked to autoimmunity. Autoimmunity is where the immune system, which normally protects the body, mistakenly attacks healthy muscle tissue. There are also changes not directly caused by inflammation, such as abnormal proteins building up in the muscles and problems with the cells that produce energy (mitochondria). Researchers are still working to understand how these changes happen and how they relate to inflammation.

IBM is not an inherited condition. It is referred to as being ‘sporadic’ rather than ‘hereditary’. There is usually no family history of IBM, and it is unusual for more than one person in a family to have IBM. In rare circumstances, genetic muscle disorders can cause a similar pattern of muscle weakness to IBM. These conditions are sometimes referred to as ‘hereditary IBM’, although they are different in terms of the way they progress over time and the abnormalities seen inside the muscle cells.

Some genes have been found that may increase the risk of developing IBM, but it’s likely that many other genetic and environmental factors need to happen together to result in someone developing the condition. In summary, there is no simple genetic cause of IBM, and it is very unlikely that family members will inherit the condition.

IBM can be diagnosed using a clinical examination and a combination of tests carried out by a specialist. These may include blood tests to check creatine kinase (CK) levels and sometimes a test for a specific antibody called cN1a. Other tests may include an electromyography (EMG), a magnetic resonance imaging (MRI) scan, and a muscle biopsy. Muscle biopsy is an important diagnostic test where a small sample of muscle, usually from the thigh, is taken and examined under a microscope. In IBM, the muscles show signs of inflammation and damage under the microscope. Abnormal proteins and changes of mitochondrial dysfunction can be seen.

Early signs and symptoms of IBM may not be recognised at first, which can delay diagnosis for some people. However, in some cases, the pattern of muscle weakness may be so typical for IBM that further tests may not be needed.

For more information, see our diagnosis page.

A multi-disciplinary approach to managing the condition and symptoms is important to improve wellbeing. Unlike other types of myositis, immune-suppressing medications like steroids are not proven to be effective for IBM because they do not stop long-term muscle weakening and wasting.

Access to a healthcare team

People with IBM should have access to a multi-disciplinary healthcare team. A multi-disciplinary approach involves different healthcare professionals working together. Usually, the lead professional will be a neurologist or rheumatologist. A neurologist is a doctor who specialises in conditions that affect the muscles and nervous system. A rheumatologist is a doctor who specialises in inflammatory conditions that affect the joints and muscles. If you’re not in contact with a specialist doctor, speak to your GP about getting access to one.

Exercise and physiotherapy

People with IBM are encouraged to stay active and do regular gentle exercise. A physiotherapist is a healthcare professional who helps manage symptoms through movement, exercise, and manual therapy. They can assess a person’s needs and put together a suitable exercise plan to help maintain muscle strength and flexibility. All exercise needs to be done safely, as falls can cause injuries that affect mobility. For advice for adults, see exercising with a muscle wasting condition.

Mobility and aids

As IBM progresses, people may need to use walking aids and wheelchairs to maintain mobility. A physiotherapist can provide advice on suitable aids and create a wheelchair-based exercise plan if needed.

Occupational therapy services aim to help people who are having difficulties with everyday tasks. They develop practical solutions and provide aids and equipment to make life at home more manageable. Some minor aids can be provided for free. Information on how to access local occupational therapy services can be found on local council websites or through a GP.

Swallowing and nutrition

Swallowing difficulties (dysphagia) should be assessed by a speech and language therapist. Dysphagia can lead to choking and coughing while eating. A speech and language therapist can provide strategies to avoid complications while eating and drinking and offer swallowing therapy to maintain as much swallowing function as possible.

If swallowing difficulties are severe and cause unplanned weight loss, a dietitian can advise on adapting or supplementing the diet, such as suggesting softer foods or nutritional supplements. They can also explore other options, such as a feeding tube if necessary.