AIPPG 2003 Dental MCQ Answer 02

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Lead is a naturally occurring heavy metal. Due to its extensive use in many areas of industry and its prolonged half-life, its presence in the environment is now ubiquitous. It has many health consequences to pediatric patients.

Key Pharmacokinetics Points

When lead is first absorbed it enters the bloodstream where 99% is bound to red blood cells. From here it is redistributed to other areas of the body. In adults 95% of lead is stored in bone as compared to 70% in children. For children the remainder is distributed to many other areas of the body including the liver, kidneys, and brain. Lead's half life in these tissue compartments is prolonged.

Pathophysiology

The effects of lead are widespread. Much of lead's toxicity is in its inherent affinity for the biologically active sulfhydryl groups possessed by vital proteins in the body (receptors, enzymes, etc.). Inhibition or interference with these proteins then leads to clinical symptoms. One example is the inhibition of enzymes involved in heme synthesis. This subsequently leads to anemia. Similar disarray can occur in multiple organ systems with lead toxicity. In developing children, these effects are magnified in a neurologic system that is extensively growing and changing.

Clinical Symptoms

Symptoms are dependent on the degree of exposure - which can correlate with blood lead levels -especially if time has passed for blood lead to equilibrate with the other organ compartments. Below are some general examples of clinical symptoms that one may expect at a given blood lead level. These are generalizations and may not apply in every case.

10 mcg/dL - may appear asymptomatic, but child may have subtle cognitive deficits including: impaired cognition, behavior disorders, impaired fine-motor coordination, poor growth, and hearing deficits.

50-70 mcg/dL - neurologic exam may reveal an irritable or lethargic child. Anemia may be present. Gastrointestinal findings include: intermittent vomiting, abdominal pain ("lead colic"), and anorexia.

70-100 mcg/dL - encephalopathy (coma, seizures, ataxia, signs of rising intracranial pressure, loss of developmental skills)

Treatment

Removal from the exposure is the first step. This may require the involvement of medical social work and initial inpatient treatment/evaluation.

For lead level above 45, the CDC recommends chelation therapy. Oral chelation therapy with succimer is the preferred choice for children who are not manifesting signs or symptoms of CNS toxicity and whose levels are less than 70. For children who are manifesting CNS signs or symptoms suggestive of encephalopathy, BAL (British anti-lewsite) should be administered first by intramuscular (IM) injection (mixed with Procaine) and then followed 4 hours later by EDTA (edetate calcium disodium). BAL is IM only, is suspended in peanut oil, is eliminated by both renal and biliary excretion, and fully crosses the blood brain barrier (it is the only parenteral chelator that crosses the blood brain barrier).