An Overview of Inclusion Body Myositis

Inclusion Body Myositis (IBM) is an acquired progressive muscular disorder and one of several types of inflammatory myopathies. It causes inflammation that damages muscles, especially in the limbs. IBM develops over time and is most commonly diagnosed in men over the age of 50.

In patients with IBM, inflammatory cells infiltrate the muscles of the body, especially in the hands, arms, legs, and feet. Once they accumulate, protein "bodies" discarded by the cells build up and cause the muscle to degrade, leading to progressive symptoms of weakness and wasting (atrophy). The presence of these damaging "inclusion bodies" in the muscles gives the condition its name.

Symptoms

The symptoms of IBM usually take time to develop, rather than coming on suddenly. It may be that patients who later find out they have IBM look back at the preceding months, or even years, and realize that some symptoms they had been experiencing were related to the condition.

Initially, people with IBM may notice they are having trouble gripping or holding objects. If the muscles of the legs are affected, patients may stumble, trip, or even fall. Sometimes people with IBM only experience symptoms related to weakness on one side of the body. In about half of patients, the muscles of the esophagus are involved, which can make it difficult to swallow (dysphagia).

Other common symptoms of IBM include:

• Trouble walking
• Difficulty climbing stairs
• Difficulty getting up from a chair
• Weakness in the fingers, hands, arms, legs, and feet
• Weakness in the muscles of the face, particularly the eyelids
• Difficulty with tasks like fastening a button or gripping objects
• Some patients experience pain as muscle damage increases
• "Foot drop" sensation which can lead to stumbles, trips, and falls
• Changes to handwriting or having a hard time using a pen or pencil
• A change in the appearance of the quadricep muscles of the thigh (wasting)

While the muscles of the heart and the lungs are affected in other types of myopathy, they are not affected in patients with IBM.

The symptoms of IBM develop slowly—usually over the course of several months or even years. It is believed that the older a patient is when they begin experiencing symptoms, the more aggressively the condition will progress.

Many people who have IBM will eventually need some help with day-to-day living, most often within 15 years of receiving a diagnosis. This could include mobility aids such as canes, walkers, or wheelchairs.

While IBM can lead to disability, it does not appear to shorten a person's lifespan.

Causes

The cause of IBM is not known. Researchers believe that, as with many conditions, a combination of factors related to a person's lifestyle, environment, and immune system play a role. Some research has suggested that exposure to certain viruses may trigger the immune system to begin attacking normal, healthy, muscle tissue. In other studies, taking certain medications have been thought to contribute to a person's lifetime risk of developing IBM.

Researchers don't think IBM is an inherited condition, but genetics are likely involved together with other factors. Some people may have genes that, while they don't cause IBM, could make them more likely to develop the condition in their lifetime (genetic predisposition).

Diagnosis

IBM is considered a disease of adult onset. Children do not get IBM and the condition is rarely diagnosed in people younger than 50. The disease is more commonly diagnosed in men, though it also affects women.

A doctor will make a diagnosis of IBM after a thorough physical examination and careful consideration of a patient's symptoms and medical history. Sometimes they will order tests that assess how well the nerves of the muscles are functioning (electromyography or nerve conduction study). They may also take samples of the muscle tissue for examination under a microscope (biopsy).

A lab test that measures the levels of creatine kinase (CK) in the blood may also be used. CK is an enzyme released from muscles that have been damaged. While CK levels can be elevated in patients with myopathies, patients with IBM often have only mildly elevated or even normal levels of CK.

Since IBM is a condition where the body attacks its own tissues, a doctor may also order tests to look for antibodies commonly found in patients with autoimmune disease. Though because treatments typically used for autoimmune conditions don't consistently work for all patients with IBM, researchers are still not sure if IBM is truly an inflammatory disease.

Treatment

There is currently no cure for inclusion body myositis. Even with treatment, the disease will get worse over time—though the progression is usually slow. People who have been diagnosed with IBM often benefit from working with physical or occupational therapists to help strengthen their muscles. Developing strategies to avoid falls, including the use of mobility aids, is also important to help patients stay safe.

A Word From Verywell

Inclusion body myositis is a progressive muscular disorder and one of several types of inflammatory myopathies. It is generally diagnosed in men over the age of 50, but women can also be affected. It causes damage to the muscles that leads to weakness which develops slowly, usually over the course of months to years. Researchers aren't sure what causes IBM, but it's believed that environment and genetics likely play a role. While there's currently no cure for IBM and it can lead to disability, the condition is not life-threatening and doesn't appear to shorten a person's lifespan.