[Symmetry and temporal variability of neurography]

The aims of the present study are to document side-to-side differences and temporal variability, between two trials (T1 and T2 at a time interval of 3 months) of nerve conduction measurements collected from 30 healthy subjects (mean age 22 +/- 2 years).

The protocol at T1 consisted of motor nerve conduction studies of median, ulnar, peroneal and tibial nerves bilaterally, with measurement of (a) motor response size (amplitude and area); (b) terminal latency; (c) minimal, mean and maximal F-wave latency; (d) motor conduction velocity; and (e) F-wave occurrence. T1 also involved sensory nerve conduction studies of median, ulnar, radial, lateral and medial cutaneous, sural and superficial peroneal nerves bilaterally, with measurement of sensory potential size (amplitude and area) and computation of sensory conduction velocity. The protocol at T2 consisted of identical measurements from the dominant side.

There was a negative relationship between the variability of parameters evaluating nervous conduction and the length of the nerve segment under study. Thus, the smallest side-to-side and temporal variabilities are measured for minimal F-wave latencies (on average 2-3%). The limits of symmetry and temporal variability are particularly useful for diagnosis of unilateral peripheral neuropathy or neurophysiological follow-up of patients with neuropathy, when the variability of the parameter under study is weak and when there is a high correlation between values recorded on the left and on the right or at T1 and T2. This was the case for motor response size of tibial and ulnar nerves, sensory potential size of radial nerve and minimal F-wave latencies from each studied motor nerve.