Peering behind the Curtain of Electrodiagnostic Testing

Electrodiagnostic studies can be used to assess disorders of the peripheral nervous system by measuring nerve function directly and objectively. An understanding of how electrodiagnosis produces relevant information can help surgeons make effective referrals and apply the results to guide patient care. An electrodiagnostic consultation is tailored to the clinical impression and adjusted dynamically to evaluate specific impairments and distinguish among differential diagnoses. The electrodiagnostic study comprises nerve conduction studies and electromyography. With nerve conduction studies, sensory and motor nerve fascicles are assessed for focal or generalized slowing of action potential conduction (which can suggest demyelination), conduction block, and amplitude loss (which can suggest axonal loss). The motor components are most useful when planning nerve reconstruction, as the recorded amplitudes can be used to evaluate for the presence of conduction block and estimate extent of axonal loss in the innervation of key muscles. The electromyography component is qualitative, assessing an array of muscles using a needle electrode that detects small amounts of recent or active axonal loss (ie, presence of fibrillations) and gauges the degree and extent of reinnervation. Electrodiagnosis can provide information on lesion localization, underlying pathophysiology, extent of nerve injury, time course, and reinnervation status. Where clinical recovery is questionable, including before or after nerve reconstruction, electrodiagnostic studies can be used to evaluate for early reinnervation and inform prognosis for recovery.