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 according to the Cleveland Clinic include:

• Difficulty with gripping, pinching, and buttoning.
• Weakness of the wrist and finger muscles.
• Atrophy of the muscles of the forearms.
• Weakness and visible wasting of the quadriceps muscles
• Weakness of the lower leg muscles, below the knees.
• Weakness of the esophageal muscles, leading to dysphagia in up to 30 to 40% of patients.
• Weakness of other muscle groups as the disease progresses.

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. Additionally, 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. Almost a decade ago, Researchers concluded a combination of factors related to a person's lifestyle, environment, and the immune system play a role in the condition. Some research suggests that exposure to certain viruses, including HIV, may trigger the immune system to attack normal, healthy muscle tissue. In other studies, certain medications, including Arimoclomol, Bimagrumab, Follistatin, and Rapamycin, often called Sirolimus, were suspected of contributing to a lifetime risk of developing IBM.

While, researchers don't think IBM is an inherited condition, a 2017 medical study suggested a possible "genetic" overlap with IBM and other autoimmune disorders. 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. According to the Myositis Association, children do not get IBM, and the condition is rarely diagnosed in people younger than 50, further reporting the disease is more commonly diagnosed in men, though it also affects women.

IBM diagnosis is found by a physical examination and personal and family medical history review, and by testing the electrical activity in the muscle, and performing a muscle biopsy, reports the Muscular Dystrophy Association, (MDA). 

The MDA also details how creatine kinase (CK) lab tests are also used to diagnosis the condition. 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. John Hopkins Medicine reports 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.