Neurology for MRCP Part 2

A 63-year-old man is admitted with confusion and a sodium of 106 mmol/L, thought to be due to thiazide use and poor intake. Over the first 24 hours his sodium is corrected to 128 mmol/L. He initially improves, but four days later develops progressive dysarthria, dysphagia and a spastic quadriparesis with preserved consciousness. What is the most likely diagnosis?

1. Basilar artery thrombosis A genuine differential for a locked-in presentation, but it is sudden rather than progressive over days and would not follow this exact correction history.
2. Wernicke encephalopathy Wrong. The triad is confusion, ophthalmoplegia and ataxia, and consciousness is typically clouded. It does not produce a spastic quadriparesis with preserved awareness.
3. Cerebral oedema from under-correction Wrong direction. Cerebral oedema complicates hyponatraemia itself or over-rapid water administration, presents acutely rather than after a four-day lucid interval, and would not produce this brainstem syndrome.
4. Osmotic demyelination syndrome correct Correct. A rise of 22 mmol/L in 24 hours is far beyond the safe limit. The characteristic course is initial improvement followed by a delayed, biphasic deterioration two to seven days later with pontine signs and, in severe cases, a locked-in picture.
5. Non-convulsive status epilepticus Wrong. It causes fluctuating consciousness and automatisms rather than a fixed progressive spastic quadriparesis with intact awareness.

The point: Correct chronic hyponatraemia by no more than 8 to 10 mmol/L in 24 hours, and slower still in high-risk patients: alcohol dependence, malnutrition, hypokalaemia, liver disease. If you overshoot, relowering with dextrose and desmopressin is an established rescue. Symptomatic severe hyponatraemia still gets hypertonic saline. The limit is on the 24-hour total, not on the initial emergency correction.

Source: European clinical practice guideline on diagnosis and treatment of hyponatraemia ERA (European Renal Association) · tier 2, specialty society or college