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 100 mcg/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. One study showed altered hippocampal volume and brain metabolites in workers occupationally exposed to lead.¹ Another showed a significant increase in the frequency of chromosomal aberrations in workers exposed to lead compared to the controls.²

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.³

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
• Deliberate ingestion (pica) is occasionally seen in adults as part of a psychiatric condition⁴
• Use of various imported tonics, alternative medication⁵ 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 remedies⁶
• Age - compared to an adult, a child can absorb twice as much lead from the GI tract
• One study reports the emergence of lead poisoning in a pregnant woman years after exposure - presumably due to increased reabsorption of lead from the skeletal system⁷

Symptoms

• Mild poisoning - lethargy with occasional abdominal discomfort¹⁰
• 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
  • Autonomic dysfunction¹¹

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.¹⁰

Other 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
  • <100 mcg/L - normal
  • >100 mcg/L - may cause impaired cognitive development in children
  • >450 mcg/L - GI symptoms in adults and children
  • >700 mcg/L - high risk of acute CNS symptoms
  • >1000 mcg/L - may be life threatening
• One study suggests that levels less than 100 mcg/L can affect physical and mental development in children¹²
• Full blood count - basophilic stippling of erythrocytes may be seen

Radio-imaging⁸

• 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.^13,14
• CT or MRI scan of the brain may be contributory in patients with symptoms suggestive of encephalopathy.

• For mild lead poisoning (<450 mcg/L) it may be sufficient to detect the source of the exposure, remove the patient from it and monitor the clinical status.¹⁵
• 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 450-600 mcg/L.
• D-Penicillamine is a commonly used but unlicensed medication. Lower dose ranges (15 mg/kg/day) are to be preferred due to the adverse effects (mainly white cell and platelet count suppression).¹⁶
• Dimercaptosuccinic Acid (DMSA, Succimer) is an alternative oral agent. There is some evidence that it can affect growth rate in children.¹⁷
• Severe lead poisoning (levels > 600 mcg/L) 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-Lewisite, 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.¹⁸ It may be used IM or intravenously (IV). There is a growing trend to administer it by slow IV 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.⁸

• 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.⁹

• 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 100 mcg/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.¹⁹
• Global reduction in the use of lead-containing petrol has resulted in a significant reduction in exposure. However, new sources continue to emerge, including improper disposal of electronics and children's toys contaminated with lead.²⁰
• Educating patients to be cautious in the use of folk remedies is however still an issue.⁶
• Further work needs to be done to reduce occupational exposure, particularly in the demolition and tank cleaning industries.²¹
• In Uruguay, a wide range of measures have been instigated including reduction of industrial and non-industrial exposure (e.g. metallurgical industries, lead-acid battery processing, lead wire and pipe factories, metal foundries, metal recyclers, leaded gasoline,lead water pipes in old houses, and scrap and smelter solid wastes).²²