CHRONIC NEUROLOGICAL DISEASE AS A POSSIBLE FORM OF LEAD POISONING

It has long been known that the clinical manifestations of lesions in the nervous system produced by lead are diverse and may simulate the symptoms of various chronic neurological diseases. This suggested to early workers that lead might be an aetiological agent in such diseases. Later, the failure to demonstrate the presence of other features of classical lead poisoning such as colic, anaemia, and basophilic stippling of the red cells in these conditions, and any correlation with exposure to an occupational hazard, demanded the modification of the original theory, and there remained the possibility that lead ingested in sub-toxic amounts may eventually produce these chronic, atypical forms of poisoning. Disseminated sclerosis is a particular example. The old theory championed by Oppenheim that lead is the causative factor was revived in a modified form by Cone, Russel, and Harwood (1934), who suggested that the demyelination is produced by lead which is mobilized from skeletal deposits before relapse. They put forward analytical results in support of this view. Lead was detected in the cerebrospinal fluid of six out of eight patients with this disease, and was-estimated in the faeces and urine and also in the spinal cord of another patient. Their results for cerebrospinal fluid are not in agreement with those of Rabinowitch, Dingwall, and Mackay (1933) and Boshes (1935). However, with the advent of more accurate and sensitive analytical methods it was realized that the findings of Cone and others were of no aetiological significance since similar amounts of lead may occur in most normal human fluids and tissue " as an inevitable consequence of life on a lead-bearing planet" (Kehoe, Thamann, and Cholak, 1933). A new light was thrown on human demyelinating diseases by the discovery that swayback, a similar disease of lambs, was associated either with a dietary deficiency of copper or with a defect in its utilization by the nervous system, and could be prevented by the administration of copper to the pregnant ewe. Since the incidence of the disease tended to follow the geological occurrence of lead in Derbyshire and the sheep were found to have absorbed abnormal amounts of this metal from their diet, it was suggested that lead might be reported that teeth from patients with disseminated sclerosis contained on the average a significantly higher concentration of lead than was present in the teeth of normal healthy people. They discovered a high incidence of this …