Diagnosis of Myopathies

Although the diagnostic work-up for myopathies can be difficult, it should be carried out for medical and financial reasons if the suspicion is supported by evidence. The diagnosis is based on the history, neurological investigation, blood chemical investigations at rest and under stress, electromyography, muscle MRI, biopsy, the in-vitro coffeine-halothan contracture test, and molecular genetic studies. There is some role for muscle enzyme determinations in the diagnostic work-up, although these values are frequently multifactorial. However, if muscle enzymes are repeatedly increased without explanation but in the presence of muscular symptoms, the diagnostic work-up should be initiated. Stress tests can be of some additional help. Needle electromyography may be normal, myogenic, neurogenic or non-specifically abnormal. Muscle MRI may show trophic disturbances, and may guide one to the muscle most adequate for biopsy. A muscle biopsy may be taken for a number of further investigations and may lead to the correct diagnosis. Only if there is a profound suspicion for a certain genetic defect, molecular genetic investigations should be initiated. In the case that a pathogenic mutation is found, genetic counselling, and assessment of the prognosis, and therapy can be initiated. For diagnostic, therapeutic and prognostic implications, diagnostic work-up should be carried out as soon as possible if myopathy is suspected.