The specific diagnosis, however, is generally made by examining a small piece of muscle from a muscle biopsy.
Before doing a muscle biopsy, clinicians may also perform other tests. One of these tests may be a blood test, which measures the level of a muscle protein called creatine kinase (or CK). This enzyme is usually found in the muscles, however following muscle damage it can leak into the bloodstream.
Muscle ultrasound may also help to detect abnormalities in the muscle. This technique is very simple, similar to the ultrasound studies carried out in pregnancy, and may provide further evidence of the involvement of the muscle.
Muscle magnetic resonance imaging (MRI), like muscle ultrasound, can assist in demonstrating patterns of muscle involvement, which can be specific to particular muscle conditions.
A muscle biopsy involves removing a small piece of muscle, usually from the thigh. When the muscle is studied under the microscope, it is possible to look for changes that might indicate a muscular dystrophy. These changes could include a variation in muscle fibre size and the replacement of some fibres by fat and fibrous tissue.
Genetic tests looking for mutations in SEPN1, the gene responsible for SEPN1-related myopathy, can provide a definitive diagnosis. These tests are now available in the UK at a specific nationally-designated laboratory. If you would like to have these genetic tests, ask your neurologist for a referral to the nearest designated laboratory to you.
Pre-natal diagnosis may be possible in SEPN1-related myopathy. In families who have a child with SEPN1-related myopathy, in whom the genetic mutations have been identified and who decide to have another baby, it is possible early in the pregnancy to detect whether the baby has the same mutations.