Wernicke Encephalopathy Masked by Prior Dextrose Administration
A 58-year-old man with a 30-year history of heavy alcohol use is brought in by his sister because of 3 weeks of confusion and unsteady gait. He denies drinking for 10 days but has had poor oral intake. On exam: alert but disoriented to date, horizontal nystagmus on lateral gaze, ataxia, and confabulation when asked about recent events. He has bilateral lower-extremity weakness and decreased vibratory sensation. MRI shows symmetric T2 hyperintensity in the mammillary bodies and medial thalami, with mammillary body atrophy. Labs: sodium 128 mmol/L, glucose 86 mg/dL, ammonia 42 µmol/L, INR 1.2, albumin 3.4, thiamine not yet drawn. He was given 1 L of 5% dextrose in water at a previous urgent care visit for 'dehydration' 5 days ago.
1. What is the most likely neurologic diagnosis, and what is the immediate treatment priority?
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The triad of encephalopathy, oculomotor dysfunction, and ataxia strongly suggests Wernicke encephalopathy, and the MRI findings in the mammillary bodies and medial thalami support it. The prior dextrose administration is a classic precipitant because glucose metabolism consumes thiamine. Do not wait for a thiamine level to treat.
Give parenteral thiamine immediately, before any further glucose-containing fluids. A common regimen is 500 mg IV three times daily for 2–3 days, followed by 250 mg daily, with dosing adjusted to local protocols. Also replace magnesium, because magnesium is required for thiamine-dependent enzymes. Monitor for improvement in eye movements and ataxia; mental status may lag.
2. How do you differentiate this from hepatic encephalopathy and osmotic demyelination syndrome?
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Hepatic encephalopathy usually produces asterixis, altered sleep-wake pattern, and elevated ammonia, often with a precipitant such as infection or bleeding. This patient has a normal ammonia and no asterixis, and his nystagmus and ataxia are not typical of hepatic encephalopathy. Osmotic demyelination syndrome follows rapid correction of hyponatremia and can cause pontine or extrapontine signal changes, but his sodium is 128 mmol/L and there is no evidence of a rapid rise; the mammillary body involvement is more characteristic of Wernicke disease.
Other considerations include alcohol-related cerebellar degeneration, subdural hematoma, stroke, and peripheral neuropathy. The combination of acute confusion, nystagmus, ataxia, and mammillary body changes makes Wernicke the leading diagnosis, with Korsakoff syndrome as the chronic cognitive consequence.
3. What long-term cognitive and functional prognosis should be discussed, and what prevents recurrence?
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Some patients recover fully with prompt thiamine, but a substantial minority develop persistent Korsakoff syndrome with anterograde amnesia and confabulation. The ataxia and eye findings may improve before memory does. Explain that abstinence from alcohol and continued thiamine supplementation are the most important steps to prevent recurrence and further injury.
Arrange cognitive rehabilitation, nutritional support, and treatment for alcohol use disorder. Family members should understand that confabulation is not deliberate lying. There is no proven drug that reverses established Korsakoff syndrome; medications such as donepezil have been studied without consistent benefit. Follow-up should include neurologic and addiction care.