Q: Rapid correction of which electrolyte derangement results in osmotic demyelination syndrome?
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A: Hyponatremia. In context of chronic low plasma sodium, the brain compensates by decreasing the levels of osmolytes (inositol, betaine, glutamine, glucose) so that brain cells can remain relatively isotonic and not absorb too much fluid. With correction of hyponatremia with IV fluids, extracellular tonicity increases, followed by an increase in intracellular tonicity (by cell making more intracellular osmolytes). Sodium should not be corrected more than 0.5 mEq/L/hr. Other rapid shifts of other osmolytes like glucose can also result in osmotic demyelination syndrome as well.
Q: Osmotic demyelination syndrome is characterized by massive axonal demyelination of which brain stem area?
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A: Pons. This is caused by overly rapid intravenous correction of hyponatremia - "from low to high, your pons will die". In context of chronic low plasma sodium, the brain compensates by decreasing the levels of osmolytes (inositol, betaine, glutamine, glucose) so that brain cells can remain relatively isotonic and not absorb too much fluid. With correction of hyponatremia with IV fluids, extracellular tonicity increases, followed by an increase in intracellular tonicity (by cells making more intracellular osmolytes). If correction is too rapid, not enough time is allowed for brain cells to adjust to new tonicity there is not enough time to increase osmolytes. Therefore, the intracellular water will be pulled out to balance the extracellular tonicity. This can lead to cellular dysfunction and central pontine myelinolysis. Myelin sheaths in the pons become damaged.
Q: Osmotic demyelination syndrome classically presents as what syndrome?
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A: "locked-in syndrome". Other symptoms include acute paralysis, dysarthria, dysphagia, diplopia, and loss of consciousness.