Blood testing may be used to measure serum creatine kinase, which ranges from normal to slightly elevated in those with BD. Skeletal muscle biopsies are used to examine muscle fibers. Biopsies in individuals with BD often show variation in muscle fiber size, atrophied fast-twitch muscle fibers, and increased nuclei number. Electromyography (EMG) can be used in diagnosis to rule out myotonia, or muscle stiffness that is detected by EMG. Individuals with BD have stiff muscles but normal EMG results (pseudo-myotonia), where no myotonic discharges are detected. Genetic testing may also be used in the diagnosis of BD to look for mutations in ATP2A1. Since only some forms of the disease are associated with ATP2A1, results of genetic testing do not always confirm a diagnosis of BD, but are useful to rule out other similar disorders.
