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.
- 1. Lead Poisoning
- a. Central Nervous System Effects
1) Pathogenesis: lead forms covalent bonds with sulfhydryl groups in proteins
and inactivates proteins; lead may affect neurotransmission; lead inhibits
aerobic energy metabolism in young animals
2) Age dependence: children are more likely to show CNS effects of lead
poisoning
3) Locations: cerebral and cerebellar cortex
4) Pathological changes: edema, white matter necrosis, vascular proliferation,
glial proliferation, neuronal damage
5) Clinical signs:
(a) acute cases: signs of increased intracranial pressure, seizures, ataxia,
may progress to coma
(b)chronic cases: seizures, attention deficits, loss of motor
skills, mental deficits, weakness, anemia.
- b. Peripheral Nervous System Effects
- 1) Location: specifically affects motor nerves
2) Pathological changes: segmental demyelination early; degeneration of
axons and myelin later
3) Clinical signs: weakness in the distribution of affected nerves; usually
distal, e.g. wrist-drop; slowed nerve conduction
- 2. Other Heavy Metals
- a. Chronic arsenic poisoning causes primarily sensory neuropathy.
- b. Mercury has a variety of effects, including extra-pyramidal and
cerebellar signs, mental fatigue, polyneuropathy