An electromyography, a nerve conduction velocities (NCV) test, or a muscle or nerve biopsy are primarily used if molecular genetic testing of SMN1 does not identify mutations.
An electromyography (EMG) is a test used to assess the health of muscles and the nerve cells that control them – the motor neurons. An electrical recording of muscle activity is made to help diagnose a neuromuscular disease, such as SMA.
The stimulation of the motor neurons produce electrical activity in the muscle, which in turn contract. The EMG machine registers this electrical activity through a needle electrode that is inserted into the muscle and connected to a recording device. The EMG can determine whether the muscles are responding to stimulation or not.
Most of the time, an EMG is performed to help diagnose diseases that cause muscle weakness. Other symptoms for which EMG may be useful include numbness, atrophy, stiffness, fasciculation, cramps, deformity and spasticity. EMG results can help determine whether symptoms are due to a muscle disease or a neurological disorder, and when combined with clinical findings, usually allow a confident diagnosis.
The needle electrodes used in an electromyography can cause some discomfort or pain to the patient. Insertion of the needles can cause similar pain to receiving an injection, while the electrical current that is sent through the needle can also cause discomfort. Patients or parents of patients can ask technicians to take a short break in order to mitigate any pain or discomfort during the procedure.
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