If JDM is suspected, blood tests are the first step to confirm that there is a problem. Taking blood tests over time helps us to work out how active or quiet your child’s illness is. Blood tests are also used to monitor medicines. Muscle enzymes are measured, including CK (creatine kinase) and LDH (lactate dehydrogenase), which are enzymes that leak from inflamed or damaged muscles into the bloodstream. Liver enzymes are measured, including AST and ALT, as these can be high due to muscle inflammation. Blood tests also show if the child’s body is producing antibodies (like Antinuclear Antibodies, or ANA) against its own cells.
The next step is generally an MRI (Magnetic Resonance Imaging), which can detect muscle inflammation. Sometimes X-rays of the chest or joints may be taken to rule out their eventual involvement or to look for calcinosis in the arms or legs. A muscle biopsy may be performed (usually under general anaesthesia) to confirm the diagnosis, this means that a small amount of muscle (usually from the thigh) may be removed for examination to determine if and how much the muscles and blood vessels have been affected by the disease. If required, a skin biopsy can be done at the same time as well to examine the disease in the skin. Other tests and procedures that may be carried out include: lung function tests, ECG (heart function), abdominal ultrasound, CT scan and EMG (muscle test)