Lead is a heavy steel-gray metal. Metallic lead and all its salts are poisonous. It is used in storage batteries, paints, hair dyes, electric cable insulation, ceramics and petrol. The principal salts which produce toxic effects are:
- Lead acetate (sugar of lead)- white crystals, previously used in medicine as an astringent and local sedatives for sprains.
- Lead carbonate (safeda)- a white crystalline powder used for manufacture of paint.
- Lead chromate: a bright yellow powder
- Lead monoxide (litharge)- pale brick red or orange masses
- Lead tetraoxide (red lead, vermilion, sindoor)- scarlet crystalline powder
- Lead sulphide (surma)– least toxic used for collyrium for the eyes.
It combines with sulphydryl groups and interferes with mitochondrial oxidative phosphorylation, ATPases, calcium-dependent messengers and enhances oxidation and cell apoptosis. This causes defective heme synthesis, proximal renal tubular and osteoblast dysfunction. In the CNS, it’s deleterious effects on the nerve cells and myelin sheaths and also causes cerebral edema.
FATAL DOSE: The typical lethal dose is said to be about 20g lead acetate and 40g lead carbonate.
FATAL PERIOD: In severe cases, death may occur within 24 hours. Ordinarily, fatal period may extend to 2–3 days.
The symptoms are: an astringent and metallic taste, dry throat, thirst, burning abdominal pain, nausea, vomiting, sometimes diarrhea, peripheral circulatory collapse, headache, insomnia, depression, coma and death. Cerebellar ataxia is common in children in acute poisoning.
Body appears emaciated, rigor mortis appears early. Stomach wall is swollen; mucosa is congested, grayish in color and softened with eroded patches.
The chronic poisoning due to lead is known as plumbism, saturnism. Lead is basically cumulative poison.
CAUSES OF CHRONIC LEAD POISONING
- It is ingested or inhaled. The most common source is ingestion of lead-containing dust. Inhalation of lead dust and fumes by makers of lead carbonate, paints, plumbers, glass polishers, printers and glass blowers.
- Continuous absorption from drinking water stored in lead cisterns, from tinned food contaminated with lead from solder, use of hair dyes and cosmetics containing lead.
- Per-cutaneous absorption of tetra ethyl lead in persons who handle petrol and gasoline.
- Absorption of vermilion applied to scalp.
SIGN AND SYMPTOMS
Chronic poisoning is insidious with fatigue, sleep disturbance, headache, irritability, slurred speech, stupor, ataxia, convulsions, anemia and renal failure.
Characteristic features are given below:
- Facial pallor: Earliest sign; seen round the mouth. It seems to be due to vasospasm and produced by contraction of the capillaries at the arterial side.
2. Anemia: In early stages, there may be polycythemia with polychromatophilia, but later there is anemia with karyorrhexis and dyserythropoiesis (punctate basophilia, reticulocytosis, poikilocytosis, anisocytosis), nucleated red cells (sideroblasts) and increase in mono nuclear cells. However, poly morphonuclear cells and platelets are decreased. Basophilic stippling may be present showing the presence of many dark blue-colored pinhead-sized spots in the cytoplasm of RBC due to toxic action of lead on porphyrin metabolism.
3. Burton’s/Burtonian (lead) line: A stippled blue line is seen on the gingival surface in 50-70% cases.
• It appears due to sub epithelial deposit of granules at the junction of teeth, especially near dirty or carious teeth of the upper jaw, within a week of exposure.
• It is due to formation of lead sulphide by the hydrogen sulphide formed by decomposed protein in the mouth.
4. Colic: It is usually later symptom, involving both large and small intestines, ureters and blood vessels occur in 85% of cases.
• The colic occurs at night and may be very severe (saturnine colic). During pain, the abdomen is tense.
• Individual attacks last only for few minutes, but may recur for several days or weeks.
5. Constipation: Common feature and usually precedes colic during pain, there is a desire for defecation. Diarrhea and vomiting may occur.
6.Lead palsy (Drops): It is a late and uncommon phenomenon, seen in < 10% of cases.
• It’s common in adults than in children, and mens are particularly affected.
• The paralysis is associated with degeneration of nerves and atrophy of muscles as a result of interference with phosphocreatine metabolism.
• The muscle groups affected are those most prone to fatigue. Sensory nerves are not clinically affected.
• There could be tremors, numbness, hyper aesthesia and cramps before the particular muscle weakness.
• Later, the extensor muscles of wrist (wrist drop) are affected, but the deltoid, biceps, anterior tibial (foot drop) and infrequently muscles of eye or intrinsic muscles of hand and foot are also affected.
7. Encephalopathy: Minor degree of involvement of brain function, commonly in children is present in almost every case.
• Symptoms include changes in personality, restlessness, hyperkinetic and aggressive behavior disorders, fatigability, mental dullness, learning disorders, refusal to play, headache, insomnia, vomiting, raised intracranial pressure, papilledema, visual disturbances and irritability.
There may be acute conditions, like convulsions, hallucinations, delirium, coma and death.
8. Effects on reproductive system: Lead may cause sterility in both male and female patients. In males, there may be loss of libido. In females, there could be infertility, menstrual irregularities like amenorrhea, dysmenorrhea and menorrhagia. Abortion occurs in pregnant females due to chronic atrophy or spasmodic contraction of uterus.
9. Optic atrophy: Few patients may develop blindness because of optic atrophy.
10. Retinal stippling noticed by ophthalmoscope with presence of grayish glistening lead particles within the early phase of chronic plumbism.
11. Lead osteopathy: In children and young adults, lead is deposited beyond the epiphysis of growing long bones. The deposition is promoted by calcium and vitamin D and is detectable by radiological examination. Deposition of lead at the growing ends may lead to the abnormal development.
12. Effects on circulatory system: it causes vascular constriction leading to hypertension and arteriolar degeneration.
13. Effect on kidneys: Atherosclerotic nephritis and interstitial nephritis may occur.
14. Effect on peripheral nerves: additionally to meningoencephalitis, it may cause degeneration of anterior horn cells and demyelination resulting in peripheral neuritis.
15. Hair: There may be alopecia.
- A blue line may be seen on the gums, but it is not a constant feature.
- Paralyzed muscles show fatty degeneration.
- Heart: It may be hypertrophied and there may be atherosclerosis of aorta.
- Stomach and intestines: It’s going to ulcerative or hemorrhagic changes with contraction and thickening.
- Liver and kidneys: Contracted and hard.
- Brain: Pale and swollen.
- On histology, bone marrow shows hyperplasia of leucoblasts and erythroblasts (‘immature’ white and red blood cells).
- Clinical features
- X-ray evidence of increased radio-opaque bonds or lines at the metaphyses of long bones and along margins of iliac-crest is seen in children.
- Basophilic stippling
- X- ray may show radio-opaque material in the G.I tract, if lead is ingested during preceding 36-48 hours.
ii. Potassium or sodium iodide 1-2 g TDS orally.
iii. Sodium bicarbonate 20-30 g in four or five divided doses orally.
iv. MgSO4 or sodium sulphate 8-12 g orally.
v. CaNa2EDTA in usual doses.
vi. BAL: Chelator of choice in case of renal impairment. Succimer (DMSA) is given in mild to moderate toxicity during a dose of 10 mg/kg orally every 8 h for 5 days, followed by the same dose every 12 h for 2 weeks.
vii. Correction of dietary deficiencies in iron, calcium, magnesium and zinc lowers lead absorption.
Vitamin C may be added (natural chelating agent).
viii. A diet poor in calcium, and Ammonium chloride 1 g, 3-4 times given daily. By this, lead deposited within the bones is mobilized into the blood and excreted.
ix. Symptomatic treatment.
TEST: Hydrochloric acid produces a whit precipitate, soluble in boiling water, and crystallizing on cooling.
MEDICO-LEGAL ASPECTS OF LEAD POISONING
• Acute and homicidal poisoning is rare.
• Chronic poisoning is common. There is a risk of failure to acknowledge the possibility of lead poisoning because the symptoms and signs are subtle and easily overlooked.
• Accidental chronic poisoning occurs in workers with lead.
• Lead oleate or lead tetra oxide is used as a local application for abortion. It is also used alone or used with arsenic as cattle poison.
• An individual can develop lead poisoning (plumbism) from retained lead bullets or projectiles.
• Lumbar puncture performed on the patients with lead encephalopathy and increased intracranial pressure can precipitate cerebral herniation and death.
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