Inclusion body myositis (IBM) is a degenerative and inflammatory muscle disease (myopathy) where the muscles or surrounding tissues become inflamed. The disease also causes painless weakening of the muscles. IBM gets worse over time and is sometimes misdiagnosed as treatment-resistant polymyositis. This condition is another inflammatory muscle disease that causes the same symptoms (muscle weakness). Symptoms of the disease usually begin after age 50, however, the disease has occurred earlier in some cases. IBM is more prevalent in men than women and is the most common disease in people of this age group. It accounts for 16–28 percent of inflammatory myopathies in North America.
The causes of inclusion body myositis are unknown. However, since inflammation is the signature symptom, some doctors think the disease is a type of autoimmune disorder. In cases of autoimmune disorders, the body’s immune system attacks itself. Some experts have linked IBM to infections by an unidentified virus. Other researchers think the main issue with IBM is an age-related inability of muscles to deal with destructive chemicals.
The condition usually begins with slow, progressive weakness in the muscles in the wrists, fingers, and quadriceps. The muscles in the neck and the ones that lift the front of the foot are affected in some cases as well. IBM may present itself as trouble with gripping, turning a key, buttoning a shirt, writing with a pen or pencil, and frequent stumbles.
A third of patients with IBM have weakness of the swallowing muscles. Muscle weaknesses in the neck can cause the head to drop. As the disease progresses slowly, most people remain able to walk, but may need a cane or wheelchair to travel long distances. Other patients are more profoundly affected and will need a wheelchair permanently within 10 or 15 years of the first symptoms.
Pain such as muscle cramping is not common with IBM, but can cause significant disability as it progresses.
Muscle diseases are typically diagnosed by considering the patient’s personal history, family medical history, and studying the results of a physical examination. After these examinations and investigations have been conducted, doctors may then follow up with lab tests to examine the activity within the muscles.
Usually, a muscle biopsy is ordered. If a doctor suspects the patient has inclusion body myositis, they will likely conduct a blood test to check the level of creatine kinase (CK), which is an enzyme that seeps out of muscle fibers when they are damaged. Although these levels are very high in other inflammatory myopathies, they are only mildly elevated or normal for those with IBM. A blood test may also be ordered to test for specific antibodies that may be specific to autoimmune muscle disease.
Next, an electromyogram is conducted to test the electrical activity of the muscles. This test is helpful to differentiate the diagnosis from other muscle diseases. Sometimes these tests are used to rule out any disorders that mimic the symptoms of IBM. As for the muscle biopsy, a local anesthetic will be applied and a small piece of muscle is removed to test whether the patient is suffering from IBM.
Inclusion body myositis has been treated with drugs to suppress the immune system, but has generally been ineffective. Some doctors may try medications like corticosteroids that alter the immune response, but many patients complain that the side effects outweigh any minor benefits and relief. Because of this, there is currently no effective course of treatment. Physical therapy and specific exercise regiments may help maintain mobility and keep joints active. The main treatment for people with IBM includes routine follow-up visits to the physician to assess the progression of the disease, and deal with the compromises in activity of daily living as they occur.
The life-expectancy of inclusion body myositis is not reduced, and since the disease progresses slowly, patients may experience varying degrees of disability. The changes in their bodies will eventually require adaptations to the home or work environment, and the use of mobility aids.
Researchers are continuing to gain an understanding of IBM. Scientists are observing and studying factors that may trigger the disease, such as viruses, medications and drugs, or vaccines. The goal is that one-day inflammatory myopathies like IBM can be better understood, treated, and hopefully prevented entirely.