Comparison of motor conduction abnormalities in lumbosacral radiculopathy and axonal polyneuropathy

We compared the frequencies and types of motor conduction abnormalities found in peroneal and tibial nerves of patients with either L5/S1 radiculopathies (n = 47) or axonal polyneuropathies (n = 49). In axonal neuropathies, compound muscle action potentials (CMAPs) were more likely to be either unobtainable or, if present, of low amplitude, prolonged in distal latency or both. F responses were more often absent, impersistent, or prolonged in minimal latency. In contrast, CMAPs in lumbosacral radiculopathies were more likely to be normal in both amplitude and distal latency. The most frequent F-response abnormality in radiculopathies was a prolonged maximum-minimum latency range rather than abnormalities of minimal latency or persistence. Logistic regression analysis demonstrated that different patterns of motor conduction abnormalities result from lumbosacral radiculopathy and distal axonopathies. The model was able to correctly classify disease state in 76% of subjects with a sensitivity of 74% and specificity of 80%.