Central pontine myelinosis

From Wikipedia, the free encyclopedia

Central pontine myelinolysis is a demyelinating lesion in the pons (part of the brain). Symptoms include dysphagia (difficulty swallowing) and dysarthria (diffuculty speaking).

Central pontine myelinolysis is a complication of treatment of patients with profound, life-threatening hyponatraemia (low sodium). It occurs as a consequence of a rapid rise in serum tonicity following treatment in individuals with chronic, severe hyponatraemia who have made intracellular adaptations to the prevailing hypotonicity. Individuals with hyponatremia should receive no more than 8-10mmol of sodium per day to prevent central pontine myelinosis.

In the context of chronic low plasma sodium, the brain's cells (neurons and glia) adapt by taking in a small amount of water; the net effect is to move water out of the interstium and equilibrate (or nearly so) the intracellular and extracellular tonicities. The chronic hyponatremia is thusly compensated.

With correction of the hyponatremia with intravenous fluids, the intra- and extra-cellular tonicities are again changed, this time in the opposite direction. With the use of intravenous hypertonic saline, the correction can be too quick, not allowing enough time for the brain's cells to adjust to the new tonicity. With a rise in extracellular tonicity, the cells compensate by lossing a small amount of water. This loss will continue until the intra- and extra-cellular tonicities are equal. If hypertonic therapy continues or is too rapid, the extracellular tonicity will continue to drive water out of the brain's cells, leading to cellular dysfunction and the condition of central pontine myelinolysis.