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Inclusion body myositis (IBM)

Inclusion Body Myositis

Our condition-specific alert cards provide crucial information for emergency healthcare professionals treating patients with muscle wasting conditions.


Inclusion body myositis (IBM) is a muscle wasting condition, which causes muscles to become thin and weak. It was recognised as a condition in its own right in the 1960s. It usually occurs in mid to later life and is more common in men than women.

For muscle specialists, it is the most common muscle wasting condition diagnosed in those who are over the age of 50 but it is sufficiently rare that most general practitioners (GPs) will not have looked after patients with IBM before, and many hospital doctors will not have heard of the condition.

Life-expectancy is not reduced in those with IBM, and the condition usually progresses slowly, over many years. People with IBM experience varying degrees of disability as the condition progresses, and usually require adaptations to the home or work environment, as well as the use of mobility aids.


IBM is a slowly progressing condition causing a gradual deterioration in muscle strength over years.

The muscles are often affected in an asymmetrical way with the muscles on one side of the body being weaker than those on the other side. The pattern of weakness in IBM is characteristic. The most frequently affected muscles are the quadriceps (the thigh muscles, which straighten the knee joint) and forearm muscles (that flex the wrists and fingers). Accordingly, people affected by IBM may fall and can have difficulty climbing stairs, getting out of a chair and poor hand-grip. Although many people with IBM do present with this characteristic pattern of weakness, it is not evident in everyone, particularly early in the condition. In most people the quadriceps muscles are affected first but in others the forearm or other muscles are affected first.

Swallowing muscles are affected in some people, but this is a rarely a significant problem early on and most do not encounter severe swallowing problems. The condition does not affect the heart, eyes, gut or bladder. It does not affect the function of the brain or sensation, and speech is rarely affected.

The condition itself does not cause pain. However, weakened muscles can predispose to problems such as falls resulting in injuries affecting bones, joints and soft tissues.


The short answer is that no-one knows. The presence of inflammatory cells in some muscle samples has led to the hypothesis that muscle is damaged by inflammation, caused by a virus or a misdirected immune system.

It has also been suggested that IBM is primarily a degenerative muscle condition with the deposition of abnormal proteins in the muscle that may trigger an inflammation of the muscles as a secondary part of the condition’s progression. Researchers from around the world continue to investigate the cause of IBM.

Although there are examples of two close relatives getting IBM, e.g., siblings or parent-offspring, this is extremely rare. Generally, IBM is considered an acquired rather than a genetic condition so it is very unlikely that more than one person in a family will have IBM.


A number of tests can be carried out together to make the diagnosis of IBM.

Blood test: when muscles are damaged, they release a protein into the bloodstream, called creatine kinase (CK). This can be detected in a routine blood test and may help indicate that there is a muscle condition, but not which one. In most, but not all, people with IBM, the level of this protein in the blood is raised. The raised level of CK may not be high enough to immediately suggest a muscle condition. This means that the CK level cannot be used to make a specific diagnosis of IBM. Nor can a normal CK level be used to rule out a diagnosis of IBM. Researchers have detected certain antibodies in the blood of those with IBM. Further research is needed to know whether these antibodies are detected in all cases of IBM especially in the early stages of the condition. We also need to know how specific these antibodies are for IBM. If they are not specific for IBM, these will lead to false positive results. Until we know this information, these antibody tests are not yet suitable for routine diagnosis of IBM.

Electromyography (EMG): when healthy muscles contract, they fire off a co-ordinated pattern of electrical impulses that can be detected by a tiny needle positioned in the muscle. When muscles that are not healthy contract, abnormal electrical impulses can be detected. However, although EMG may be helpful in highlighting the presence of a muscle condition, it cannot diagnose the specific condition.

Muscle imaging: imaging muscle, for example by MRI (magnetic resonance imagery), may be helpful in suggesting a possible diagnosis of IBM. However, this cannot be used to make a definitive diagnosis.

Muscle biopsy: this is a definitive test for IBM. It involves taking a small sample of muscle under local anaesthetic, for analysis in a laboratory. This process involves the use of a series of dyes and reactions, which will highlight different aspects of muscle structure and function. In IBM, muscle cells appear damaged and there is evidence of inflammation. In addition, the hallmark of IBM is the inclusion body, which is an abnormal clump of proteins, which can be seen in damaged cells with the use of specific dyes. This appearance will allow the pathologist and clinician to confirm the diagnosis of IBM. In some people, an initial biopsy may not be sufficient to make the diagnosis, and a second biopsy may be necessary. Despite all these tests, early signs and symptoms of IBM may not be recognised readily, which can delay the diagnosis for some people. Equally, in some cases, the pattern of muscle weakness may be so typical for IBM that further tests or biopsies may not be essential.


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