Muscle wasting begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy(DCM) is common, but the development of congestive heart failure or arrhythmias (irregular heartbeats) is only occasional.
* A positive Gowers' sign reflects the more severe impairment of the lower extremities muscles. The child helps himself to get up with upper extremities: first by rising to stand on his arms and knees, and then "walking" his hands up his legs to stand upright.
* Affected children usually tire more easily and have less overall strength than their peers.
* Creatine kinase (CPK-MM) levels in the bloodstream are extremely high.
* An electromyography (EMG) shows that weakness is caused by destruction of muscle tissue rather than by damage to nerves.
* Genetic testing can reveal genetic errors in the Xp21 gene.
* A muscle biopsy (immunohistochemistry or immunoblotting) or genetic test (blood test) confirms the absence of dystrophin, although improvements in genetic testing often make this unnecessary.