EMG helps to diagnose or rule out a number of conditions such as muscle disorders, such as muscular dystrophy or polymyositis, diseases affecting the connection between the nerve and the muscle, such as myasthenia gravis, disorders of nerves outside the spinal cord (peripheral nerves), such as carpal tunnel syndrome or peripheral neuropathies, disorders that affect the motor neurons in the brain or spinal cord, such as amyotrophic lateral sclerosis or polio disorders that affect the nerve root, such as a herniated disk in the spine