Childhood lead poisoning: a re-evaluation.

Long recognized as an environmental toxin of fearsome lethality, lead effects are commonly described as extremely serious, particularly as regards the central nervous system. It is postulated here that this represents only part of the pathologic spectrum. Ohter lead-related conditions, as yet unrecognized, may include a wide range of central nervous system dysfunctions that although severe, are not so acutely dramatic or widely destructive as the classic encephalopathic or preencephalopathic states. These conditions remain etiologically unrecognized primarily because of (1) the variable nature of onset, (2) the variable nature of the manifestations, (3) the relative subtlety of the dysfunctions, and most importantly, (4) the absence of consistant, unequivocal evidence demonstrating the relationship of lower blood lead levels with pathologic effects. This last is seen as pivotal, and an extensive examination of the reasons for its absence is presented. It is postulated that biological variability, a concept widely used in medicine but rarely invoked in the researching of lead toxicity, is a crucial ingredient in lead research. It is further asserted that the grevious lack of etiologic recognition will continue until that factor is incorporated into research designs.