Electrodiagnostic evaluation of motor neuron disorders

Amyotrophic lateral sclerosis (ALS) is the most common adult motor neuron disorder and leads usually to death within two to five years after diagnosis. Clinically, ALS presents with fasciculations, progressive weakness, muscle atrophy, and spasticity. It is a clinical diagnosis, supported by electrodiagnostic and laboratory tests. Nerve conduction studies (NCS) and needle electromyography (EMG) are essential in the evaluation of suspected ALS. NCS are primarily used to exclude any potentially treatable motor neuropathy that may mimic ALS. Standard nerve conduction studies should include at least four sensory and four motor nerves in an arm and leg. At least three sites in three different nerves should be stimulated when searching for conduction blocks, which may distinguish motor neuropathy from ALS. Needle EMG is very valuable as it can demonstrate widespread involvement of muscles that are not clinically weak. Characteristic findings include widespread non-myotomal denervation (both acute and chronic), with fibrillations and fasciculations. Extensive needle examination should include at least two limbs (arm and leg; at least five muscles each), thoracic paraspinal and bulbar muscles.