Lead poisoning

Lead poisoning or plumbism refers to the multi-organ toxicity exerted by exposure to lead. Manifestations differ based on a myriad of features including chronicity, exposure intensity, and age. Neurologic toxicity and haematologic toxicity are common features. Clinical manifestations vary, ranging from mild (or asymptomatic) cases to a severe life-threatening encephalopathy ⁶.

Epidemiology

Common sources of exposure to this ubiquitous metal may be broadly classified as occupational (or recreational), environmental, or perinatal (primarily trans-placental). Environmental sources may include ⁶:

• lead-based paint

  • structural renovation (e.g. sanding) or senescence (e.g. flaking) results in incorporation in soil and/or dust contamination

  • most common source of paediatric exposure

• contamination of food or water

  • degradation of lead-containing pipes and solder in plumbing

  • cans may contain lead solder

  • contamination of illegally distilled alcohol ("moonshine"), cooking spices, traditional remedies

Sources of occupational and recreational exposures include:

• lead smelting, metal work (e.g. welding)

• automobile work (especially related to radiators)

• firearm ranges

• construction workers, painters

Clinical presentation

Presenting features vary as a function of factors such as age (paediatric predisposition to more severe neurologic toxicity), ingested dose, and chronicity of exposure.

• neurologic

  • milder paediatric cases may manifest with disturbances in behaviour, growth, hearing and cognition

  • severe paediatric cases may progress to encephalopathy with seizures, coma, ataxia, cerebral oedema

  • adults may similarly demonstrate mild (tired, irritable) symptoms or a severe encephalopathy

    • peripheral motor neuropathy may also develop

• gastrointestinal

  • abdominal pain

  • vomiting

  • constipation

• haematologic

  • anaemia

    • haemolysis may also be observed

    • elevations (chronic) in zinc and erythrocyte protoporphyrin

• reproductive

  • miscarriages

  • infertility

    • may impair spermatic function and spermatogenesis

• renal

• cardiovascular

  • hypertension

• musculoskeletal

  • gout

Pathology

• bones

  • bone remodelling and growth may be affected in paediatric cases, with proposed mechanisms including ¹⁰

    • alterations in circulating endocrine factors such as parathyroid hormone and activated vitamin D

    • derangement in paracrine signalling factors such as osteocalcin

    • direct cellular toxicity, particularly affecting osteoclasts

  • growth trajectory and height may be affected

  • pathologically increased deposition of calcium in the zones of provisional calcification responsible for the dense metaphyseal bands on radiographs referred to as "lead lines"

• anaemia is multifactorial

  • ​multi-step inhibition in haem synthesis

    • including aminolevulinic acid dehydratase and ferrochelatase ⁹

  • may impair production of erythropoeitin ⁶

  • erythrocyte functional and structural derangements

    • inhibition of erythrocyte sodium-potassium pump ⁸

      • predisposing to breakdown of the cell membrane and haemolysis

    • inhibition of pyrimidine 5' nucleotidase

      • residual nucleotide clumps in cytosol appear as basophilic stippling

Radiographic features

Plain radiograph

• may show bands of increased density at the metaphyses

• can affect any metaphysis, but the involvement of the proximal fibula and distal ulnar metaphyses is highly suggestive

• may show bone-in-bone appearance

• abdominal radiographs utile for identification of exposure source and anatomic location if an ingestion is suspected ⁷

  • intra-luminal radio-opaque foreign body (or multiple punctate densities)

  • serial radiographs may be used to monitor effectiveness of bowel decontamination

Treatment and prognosis

• identification of source crucial to prevent ongoing toxicity ⁶

• meticulous supportive care

• decontamination of ongoing sources of enteral absorption (paint chips, foreign bodies)

  • endoscopic retrieval

  • whole bowel irrigation

• some patients may require chelating agents to enhance elimination

  • dimercaprol

    • also known as "British anti-Lewisite" or BAL

  • dimercaptosuccinic acid (DMSA)

    • also known as succimer, the favoured available oral chelating agent over d-penicillamine

  • edetate calcium disodium (CaNa2EDTA)

History and etymology

Lead has been used extensively since ~7000 BCE ⁵. Its chemical symbol Pb, is short for plumbum, the Latin word for lead. This is the origin of the word plumber and plumbing as lead has been widely used for water pipes in the home since Roman times, and also 'plumbism', a synonym for lead poisoning ⁵. 

Differential diagnosis

• healed rickets

• physiological appearances in <3 years' age group

See also

• differential for dense metaphyseal bands

• heavy metals