Lead Poisoning

Lead accumulates slowly in the body and even low doses can eventually lead to poisoning. Serum level of lead at which treatment is indicated in young children is 100mcg/l. 95% of lead in body is deposited in the bones and teeth while 99% of lead in blood is associated with erythrocytes. Lead poisoning can cause nervous system toxicity and renal tubular dysfunction leading to irreversible interstitial nephrosis with progressive renal impairment and hypertension. Lead also depresses haem synthesis and shortens the life span of erythrocytes causing a hypochromic microcytic anaemia.

Incidence

Lead poisoning is a lot less common than it used to be with less use in petrol, paints or cosmetics and generally improved housing. One English review which looked at hospital admissions over 15 years, 3 years' worth of mortality statistics and reports to the Health and Safety Executive found one death and 83 hospital admissions. The authors concluded that lead poisoning was rare, but when it did occur, it was associated with considerable morbidity.¹

Risk Factors

• Reclamation of lead from scrap metal, battery manufacture and other industries where lead is involved
• Children chewing lead painted items or ingesting fishing weights, bullets or contaminated soil
• Use of various imported tonics and cosmetics containing lead
• Associated iron deficiency - increases lead absorption from gastro-intestinal (GI) tract
• Poor/old housing (lead paint or pipes)
• Use of lead-containing folk remedies
• Age - compared to an adult, a child can absorb twice as much lead from the GI tract

Symptoms

• Mild poisoning - lethargy with occasional abdominal discomfort³
• Severe poisoning
  • Abdominal pain - usually diffuse abdominal pain but may be colicky
  • Vomiting
  • Constipation
  • Headaches
  • Hearing loss
  • Sub-fertility
  • Encephalopathy - commoner in children, characterised by seizures, mania, delirium and coma
  • Foot drop - due to motor peripheral neuropathy
  • Wrist drop - this is a late sign
  • Carpal tunnel syndrome

Signs

There are no pathognomonic signs, but the following may be seen:

• A blue discoloration of gum margins
• Mild anaemia
• Behavioural abnormalities (more marked in children) - irritability, restlessness, sleeplessness
• Cognitive dysfunction
• Impaired fine-motor coordination or subtle visual-spatial impairment
• Chronic distal motor neuropathy with decreased reflexes and weakness of extensor muscles in adults

This depends on the presentation. Diagnosis may be difficult in the UK where lead poisoning is a relative rarity, but the condition should be on the list in patients presenting with diffuse abdominal pain.³Other conditions which may need to be considered include:

• Acute confusional states
• Acute memory loss
• Epilepsy
• Encephalopathies
• Frontal lobe syndromes
• Depression
• Attention deficit hyperactivity disorder
• Learning disorder
• Developmental delay
• Language disorder
• Autism or pervasive developmental disorder
• Organic solvent poisoning
• Other heavy-metal poisoning
• Radial mononeuropathy and other peripheral neuropathies
• Diabetic neuropathy
• Anaemias, acute and chronic
• Constipation
• Guillain-Barré syndrome

Laboratory Tests

• Serum lead levels
  • <100mcg/l - normal.
  • >100mcg/l - may cause impaired cognitive development in children
  • >450mcg/l - GI symptoms in adults and children
  • >700mcg/l - high risk of acute CNS symptoms
  • >1000mcg/l - may be life threatening
• Full blood count - basophilic stippling of erythrocytes may be seen

Radio-imaging²

• Plain X-ray may show transverse lines in tubular bones. These are actually areas of arrested bone growth and may persists a long time after exposure ends. They are not seen in the early phase of exposure.
• Plain abdominal X-rays may show radio-opaque flecks in cases of suspected lead foreign body ingestion (e.g. pica in children).
• X-ray fluorescence works by detecting specific emissions from tissues when bombarded with X-rays. It is a sensitive method of detecting low levels of lead in the body.^4,5
• CT or MRI scan of the brain may be contributory in patients with symptoms suggestive of encephalopathy.

• For mild lead poisoning (<45mcg/dL) it may be sufficient to detect the source of the exposure, remove the patient from it, and monitor the clinical status.^6,7
• Oral chelation therapy is an option sometimes used for mild to moderate poisoning. The word chelator is derived from the Greek for claw, and chelators work by forming a tight chemical bond with heavy metals, enabling them to be excreted. Opinions vary as to when chelation therapy should be used, but it is often employed at levels of 45-60mcg/dL.
• D-Penicillamine is a commonly used but unlicensed medication. Lower dose ranges (15mg/kg/day) are to be preferred due to the adverse effects (mainly white cell and platelet count suppression).⁸
• Dimercaptosuccinic Acid (DMSA, Succimer) is an alternative oral agent. There is some evidence that it can affect growth rate in children.⁹
• Severe lead poisoning (levels > 60mcg/dL) due to acute ingestion may require:
  • Airway maintenance
  • Management of coma and seizures
  • Intravenous drip of normal saline
  • Orogastric or nasogastric catheter and irrigation with polyethylene glycol
• Parenteral chelators should be given.
• Dimercaprol (British Anti-Lewesite, BAL) - this is given intramuscularly (IM) but often results in a bad taste which patients find hard to tolerate.
• Calcium disodium edetate is another option, which is sometimes given as an adjunct in cases of encephalopathy.¹⁰ It may be used IM or intravenously (IV). There is a growing trend to administer it by slow intravenous drip.
• Chelation therapy should be withdrawn gradually to avoid the metal leaking out of the bones and causing a rebound rise in blood levels.

• Lead poisoning, with or without encephalopathy, can affect all the systems of the body.
• Hepatic, renal and neurological damage can occur.
• Chelation itself can cause problems, and treated patients can develop hypertension, raised intracranial pressure, and renal failure from the chelated lead compound.²

• The prognosis has improved considerably with aggressive treatment and there have been no reported deaths in children from lead encephalopathy in recent years.
• Cases of acute lead encephalopathy in children still occur and can result in severe neurological damage, seizure disorders, depressed school function, and learning disabilities.
• Adults tend to fare better, but long term effects can include distal motor neuropathies, depressive disorders, aggressive behaviour, defects in sexual performance and fertility problems.⁷

• The removal of paint from lead and the replacement of old lead pipes has done much to reduce the burden of lead poisoning, particularly on children. The aim has been to reduce lead levels in children to less than 100mcg/L. However, ongoing research suggests that neurotoxicity can develop at levels below this figure, and the effect of chronic low-dose exposure (e.g. due to flakes of old paint) is currently being investigated.¹¹
• Educating patients to be cautious in the use of folk remedies is however still an issue.¹²
• Further work needs to be done to reduce occupational exposure, particularly in the demolition and tank cleaning industries.¹³