I. Toxic Disorders
A. General Concepts
Toxins include: heavy metals, certain poisons, organic compounds, drugs (of addiction and/or therapy) and anesthetics. Occasionally, the mechanism of action is clear, as in the anoxic poisons, carbon monoxide and cyanide. More often the relationship of biochemical and morphological lesions is obscure. Alcohol, for example, is a depressant drug which may cause nervous system and muscle pathology directly or through metabolites or through association with nutritional deficits.
B. Heavy Metals
Heavy metals such as lead and mercury cause damage to the nervous system which is differently manifested in children and adults. Other toxins, both endogenous and exogenous, usually affect the nervous system with no age dependence. An important source of exposure to heavy metals is through occupational or environmental exposure.
1. Lead Toxicity
Infants and children are especially vulnerable to lead toxicity. Lead exposure begins in utero because lead readily crosses the placental barrier. The developing nervous system is extremely susceptible to lead toxicity. It is estimated that over 10% of preschool children have lead levels high enough to cause intellectual impairment, behavioral abnormalities, and learning deficits. A major source of lead for children is paint chips or paint dust in homes.