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.