Toxicology · Short notes

Heavy Metal Poisoning: Short Notes & Cheat Sheet

Lead, mercury, arsenic, iron and other metal poisonings: sources, features, the stages of iron poisoning, and choosing a chelator.

Short notes

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The apparent recovery in stage 2 is dangerous: patients deteriorate later if untreated.

Sources include old paint, batteries, contaminated traditional remedies and some traditional eye cosmetics (surma/kohl).
Lead inhibits δ-ALA dehydratase and ferrochelatase, causing microcytic anaemia with basophilic stippling and raised zinc protoporphyrin.
Features: abdominal colic, a blue gum line, lead lines at the growing ends of bones, wrist or foot drop, kidney damage, and encephalopathy in children.
Treatment: remove the source; oral succimer (DMSA) for moderate poisoning; dimercaprol first and then calcium disodium EDTA for encephalopathy.

Elemental mercury vapour affects lungs and brain (tremor, irritability). Inorganic mercury salts are corrosive and damage the kidneys. Organic methylmercury (from fish) is neurotoxic and teratogenic (Minamata disease).
Dimercaprol is used for inorganic mercury but avoided in methylmercury poisoning, where it can raise brain levels. Succimer or DMPS are alternatives.
Arsenic contaminates groundwater in parts of Punjab and Sindh. Acute poisoning causes a garlic odour, rice-water diarrhoea and QT prolongation.
Chronic arsenic causes thickened skin on palms and soles, 'raindrop' pigmentation, white lines on nails (Mees' lines), neuropathy and cancers. Treat with dimercaprol, succimer or DMPS.

Iron poisoning is a leading cause of fatal poisoning in young children. Doses over about 60 mg/kg of elemental iron are serious.
Stages: GI symptoms (0–6 h), an apparent recovery (6–24 h), shock and metabolic acidosis, liver failure (2–3 days), and later gastric scarring (2–6 weeks).
Activated charcoal does not bind iron. Use whole-bowel irrigation and IV desferrioxamine, which can turn urine reddish ('vin rosé').
Chronic iron overload (e.g. transfused thalassaemia, common in Pakistan) is treated with oral deferasirox or deferiprone, or desferrioxamine.
Copper builds up in Wilson's disease (penicillamine, trientine). Thallium causes hair loss (Prussian blue). Cadmium damages kidneys and bones (itai-itai disease).

High-yield facts in one place. Cover the right-hand column and test yourself.

Metal	Sign
Lead	Basophilic stippling, gum line, wrist drop
Arsenic	Mees' lines, hyperkeratosis, garlic odour
Mercury	Tremor, erethism, kidney damage
Thallium	Alopecia
Cadmium	Itai-itai (bone pain, renal)
Iron	Vomiting, then latent phase, then shock

BAL before EDTA in lead encephalopathy: Give dimercaprol first so that EDTA does not shift lead into the brain.

Use calcium disodium EDTA, never disodium EDTA, which can cause fatal hypocalcaemia.
Activated charcoal does not adsorb iron or lithium.
Dimercaprol is avoided in iron, cadmium and methylmercury poisoning.
The latent phase of iron poisoning is a false recovery; the patient still needs treatment.

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