Chronic denervation | Remote axon loss identified by long-duration, high-amplitude motor units firing with a reduced recruitment pattern | Generally denotes a process that started at least several months before the examination |
Active or ongoing denervation | A muscle exhibiting positive sharp waves or fibrillation potentials, reflecting a subacute (or more long-standing but uncompensated) neurogenic or axon-loss process | Does not always imply a truly active process. Fibrillation potentials and positive sharp waves are observed whenever a muscle fiber is awaiting reinnervation. These findings generally appear by about 3 weeks after the onset of injury and resolve within a few months, but may persist for longer in distal muscles and when reinnervation mechanisms are not fully successful or complete |
Intraspinal canal lesion or process | Electrodiagnostic testing characterized by neurogenic or axon-loss changes in muscles of 1 or more specific myotomes (eg, a spinal root or segment derivative) without sensory findings | The lesion is proximal to the dorsal root ganglion. Most of these lesions are compressive radiculopathies; but infrequently; other lesions such as motor neuron disease produce similar findings |
Neurogenic | Electrodiagnostic features resulting from lesions of the anterior horn cell, nerve root, plexus, or nerve | Neurogenic findings are further refined by distribution and the presence or absence of sensory findings |
Myopathic | Electrodiagnostic features of muscle disease, including low amplitude, short duration, and polyphasic motor units | Electrodiagnostic testing may be less sensitive in many myopathies than in neurogenic conditions |
Irritable myopathy | When myopathic features are accompanied by diffuse fibrillation potentials, positive sharp waves, or both | Suggestive of inflammatory or necrotizing etiologies, but not pathognomonic |
Motor unit instability | The same motor unit on needle electrode examination varies in morphology from one firing to the next | Indicates dysfunction at the neuromuscular junction, but it can be seen in neurogenic conditions during early reinnervation, when neuromuscular junctions are immature |
Reduced activation | Suboptimal voluntary activation of a muscle resulting from central nervous system causes | Can result from pain, cognitive dysfunction, poor effort, or upper motor neuron pathology, and indicates that the data may be of lower yield |
Conduction block | Motor response in a nerve conduction study has > 50% reduced response when stimulating at a more proximal location | Indicates focal demyelination When occurring at noncompression sites or in multiple nerves, can suggest acquired demyelinating polyneuropathies |