Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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February 17, 2022
Lead Encephalopathy
- Background:
- Lead poisoning is caused by increased levels of the heavy metal lead in the body.
- Blood lead levels should be less than 5 μg/dL in children and 20 μg/dL in adults. Lead encephalopathy may occur with lead levels over 70 μg/dL.
- Lead toxicity can affect multiple organ systems, such as the nervous system, the hematologic system, the skeletal system, the gastrointestinal system, the urinary system, the cardiovascular system, and gums.
- Lead acts as a cellular toxin by inhibiting mitochondrial respiration. The effects of lead on cellular aerobic energy metabolism could cause hemorrhage, edema, neuronal necrosis, and perivascular proteinaceous exudate in the brain.
- Lead encephalopathy is rare in adults because of the capacity of the mature brain to sequester lead away from the neurons.
- Reversible posterior white matter encephalopathy is rare in lead encephalopathy.
- Clinical Presentation:
- Encephalopathy: seizures, fatigue, headache, insomnia, and developmental and behavioral disorders, such as decreased cognitive function, memory loss, learning disorders, depression, or irritability
- Other symptoms include peripheral neuropathy (the nervous system); basophilic stippling of erythrocytes and anemia (the hematologic system); lead bands at the epiphyses of the long bones (the skeletal system); chronic or recurrent abdominal pain, constipation, loss of appetite (the gastrointestinal system); chronic tubulointerstitial renal disease (the urinary system); hypertension (the cardiovascular system); and lead lines (a line of hyperpigmentation) on gums.
- Key Diagnostic Features:
- A history of lead occupational exposure or traditional herbal medicine usage
- Red blood cells with basophilic stippling, lead lines on gums, and elevated blood/urine lead level are the hallmarks of diagnosis.
- The reported neuroimaging findings in lead encephalopathy include: 1) extensive intracranial calcifications in the cerebral cortex, the subcortical area, basal ganglia, and cerebellum on CT; and 2) hyperintensity in the periventricular white matter, basal ganglia, insula, and pons on T2WI.
- Typical evolution of neuroimaging: Progressive atrophy, specifically in the frontal gray matter and the anterior cingulate cortex on MRI, has been reported in patients with chronic lead poisoning, while hyperintensity in the white matter and basal ganglia may diminish after chelation therapy in patients with acute lead poisoning.
- Differential Diagnoses:
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Porphyria: MRI shows bilateral contrastâenhancing lesions in the posterior cortex and subcortical white matter, central pontine and extrapontine myelinolysis, and cortical laminar necrosis (if infarction). MRI of the interictal period may report multiple white matter hyperintensities on T2WI. Heme precursors such as delta-ALA and porphobilinogen in urine are raised.
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Posterior reversible encephalopathy syndrome (PRES): MRI shows reversible bilateral symmetric hyperintensities in posterior white matter. Lesions may also be located in other areas such as the anterior white matter, cerebellum, brainstem, basal ganglia, or the spinal cord. PRES is frequently observed in patients with hypertension, (pre)eclampsia, nephropathy, or during treatment with immunosuppressive agents.
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Superior sagittal sinus thrombosis: MRI reveals cerebral edema, venous infarction, hematoma, or subarachnoid hemorrhage. The triangle sign, empty delta sign, and loss of flow void in the superior sagittal sinus on MRI are frequently present.
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Progressive multifocal leukoencephalopathy (PML): PML is caused by the human polyomavirus JC. MRI shows asymmetric areas of hyperintensity in the subcortical white matter, the cerebellar peduncles, and basal ganglia without enhancement in classic PML cases.
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Hypoglycemia: MRI reveals reversible bilateral diffusion-restrictive lesions in the posterior limb of the internal capsule, frontoparietal cerebral cortex, corona radiata, centrum semiovale, hippocampus, and basal ganglia. Serum glucose level is less than 50 mg/dL.
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Osmotic demyelination syndrome (ODS): ODS usually occurs with rapid corrections in serum sodium. MRI shows lesions in central pontine and/or extrapontine areas including basal ganglia, thalami, hippocampi, and the periventricular white matter. Restricted diffusion may be present within 24 hours and contrast enhancement may appear in the subacute phase.
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Treatment:
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Chelation therapy could minimize mortality and morbidity of lead encephalopathy. Although patients will generally experience improvement in symptoms after chelation therapy, there is still a 25%–50% incidence of severe permanent sequelae after encephalopathy develops. Repeated chelation therapy may be necessary until blood lead levels return to a safe margin (≤20 µg/dL). The pace of improvement depends on the magnitude of intoxication and may range from weeks to a year.
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