Sensitive technique for detecting subclinical lead neuropathy.

443-449. Subclinical neuropathy was studied in 39 male lead workers. Although 31 had a diagnosis of poisoning, all were without clinical signs of neurological impairment. A standard electromyogram revealed abnormalities (fibrillations and/or diminished number of motor units) in 24 men. The mean maximum conduction velocities (MCV) of the ulnar and median nerve were significantly lower in the group of lead workers as compared with an age-matched control group. Measurement of the conduction velocity of the slower fibres (CVSF) of the ulnar nerve proved to be a very sensitive indicator of lead damage. This measurement was done as a modification of Hopf's technique using a partial antidromic block. A combination of this variable and the distal latency of the median nerve discriminated lead workers from controls better than any other combinations. The findings are consistent with slight neuropathy. They further show that lead also affects certain portions of the fibres in the proximal part of the nerve. The neurophysiological findings of the lead workers were collated to form a neurophysiological score (NF score). This score was used to compare the neurophysiological state with the degree of present lead effect, as judged from a rigid classification based on defined subjective symptoms and results of laboratory tests. There was poor agreement between the severity of lead effect and the NF score. No isolated laboratory test correlated with the neurophysiological findings. From these results it appears that subclinical nerve damage can be detected in lead workers with no clinical neurological symptoms. Measurement of the CVSF is a particularly sensitive method for this purpose. The lack of correlation between the severity of subclinical nerve damage and the intensity of lead effect, as judged by commonly used criteria, suggests that nerve damage is produced independently of other manifestations of poisoning. This observation indicates the need for further studies on the value of present acceptable limits of lead exposure from the point of view of the nervous system.