Also, patients should not be pressed to undergo this examination if they are fatigued. Test results are also dependent on the limb temperature, so be certain that the ambient temperature is controlled to maintain a limb temperature of 72 F. Electrodiagnosis can determine the difference between axonal and demyelinating disorders, but cannot distinguish between toxic and nontoxic etiologies. Axonal degeneration usually shows a reduction in amplitude of evoked conduction action potentials with relative preservation of nerve conduction velocities. Demyelination shows a slowing of the nerve conduction velocity, dispersion of evoked compound action potentials, conduction block, and marked prolongation of distal latencies. Nerve conduction tests usually show decreased motor and sensory nerve conduction velocities.
Nerve biopsies are useful for hexacarbon neuropathies since the results are distinctive.
Results show axonal swellings with secondary retracted myelin sheaths filled with massive neurofilament accumulations that are tightly pressed together. Some unmyelinated axons have glycogen granule accumulations in the axonal lumen. The sural nerve at the ankle is the preferred site. As mentioned previously, 2,5-HD, the proximate neurotoxin, is excreted in the urine and can be measured by a specialty laboratory. The best time for obtaining a urine sample would be at the end of the shift at the end of the workweek.