Metals and Poisons

Question 1

Discuss the two ways in which patients can present with arsenic poisoning.

Answer 1

Acute: >1 mg/kg potentially lethal. Chronic: long-term contaminated artesian water (>10 years)

Question 2

What is the toxic mechanism of arsenic?

Answer 2

Arsenic binds to cellular enzymes interfering with cellular respiration, inhibiting DNA replication/repair. Binds to the sulfhydryl group and substitutes for phosphate in ATP + it produces reactive oxygen intermediates.

Question 3

Describe the clinical features of acute arsenic toxicity.

Answer 3

After a large ingestion: rapid onset watery diarrhoea (rice water diarrhoea), vomiting, abdo pain. GI bleeding. Hypersalivation, garlic odour are characteristic. Encephalopathy, seizures and CV collapse occur within hours. ARDS/AKI/ALF and bone marrow depression. Alopecia and peripheral neuropathy develop in survivors.

Question 4

What does subacute toxicity secondary to arsenic present with?

Answer 4

GI symptoms, leukopenia, derranged LFTs and haematuria with peripheral neuropathy.

Question 5

What does chronic arsenic toxicity present with?

Answer 5

Multisystem disorder: cutaneous lesions, nail changes (Mee’s lines), painful peripheral neuropathy (glove/stocking), skin/bladder malignancies, constitutional symptomats, hyperpigmentation

Question 6

What is the immediate threat to life after acute arsenic poisoning?

Answer 6

Hypovolaemic shock secondary to profound GI losses

Question 7

What decontamination is recommended in arsenic poisoning?

Answer 7

Activated charcoal does not bind arsenic. Instead patients who have had an AXR confirming arsenic trioxide should have whole bowel irrigation with PEG.

Question 8

When is chelation indicated in arsenic toxicity?

Answer 8

Succimer, dimercaprol or 2,3-dimercaptopropane (DMPS) are indicated orally/IV when there are objective clinical features of acute arsenic toxicity or raised urinary arsenic concentration