Distribution of nerve conduction velocities in acute thallium poisoning

To assess the effects of thallium on the conduction velocities of faster and slower nerve fibers, the distribution of conduction velocities in sensory fibers of the median nerve was examined in a patient with acute thallium poisoning 2 and 11 months after the onset of symptoms. In the first examination, the patient showed evidence of a distal sensorimotor neuropathy and had an elevated urinary thallium concentration (3.5 mg/L); the conduction velocities of faster fibers were below the normal lower limit, whereas those of slower fibers were within normal limits. At the second examination, the conduction velocities of all faster and slower fibers increased and were within normal limits; clinical signs and symptoms of neuropathy almost disappeared. It is concluded that the conduction velocities of faster fibers significantly decrease in an early stage of acute thallium poisoning and recover following recuperation from the poisoning; those of slower fibers are minimally affected and then improve.