Osmotic Demyelination Syndrome

Thank you Teja, for presenting a case during our Renal Report today – a middle aged woman with post-operative hyponatremia. We discussed the basics of hyponatremia work-up/management, with an interesting discussion on osmotic demyelination syndrome.


  • Osmotic demyelination syndrome (ODS) is a very rare, but potentially fatal complication of overly rapid correction of hyponatremia.
  • Our brains start to adapt to hypotonicity/hyponatremia almost immediately, and this adaptation is complete in 2 days. Hence, in patients where hyponatremia has been present for > 2 days, slow correction of hyponatremia is critical in reducing the risk of ODS.

Osmotic Demyelination Syndrome

  • Why does it happen?
    • IMPORTANT to note that the brain begins to adapt to hypotonicity almost immediately after a fall in serum sodium, and the adaptation in complete within 2 days. This process is referred to as “cerebral adaptation to hyponatremia,” and includes processes such as loss of solutes from the brain cells, to allow for osmotic movement of water out of the cells. This is the brain’s mechanism to actively reduce cerebral edema that may occur in the setting of hyponatremia.
    • This cerebral adaptation to hyponatremia is what paradoxically leads to osmotic demyelination syndrome when hyponatremia is corrected too quickly. When hyponatremia is corrected (too quickly), the water leaves the brain cells by osmosis. These brain cells (that have already lost many of its solutes as part of their adaptation), cannot replace their osmolytes as quickly in response to the correction of hyponatremia. This leads to a rapid fall in brain volume, which results in demyelination.
    • Exactly how fall in brain volume leads to demyelination is unknown.
  • Risk Factors for Osmotic Demyelination
    • Risk increases with lower Na levels; majority of cases occur when initial Na concentrations are < 105 mEq/L
    • Duration of hyponatremia is important! Hyponatremia must have persisted for more than 1-2 days (enough time for brain to have adapted to hyponatremia).
    • Overly rapid rate of correction. Do not exceed correction rate of 6-8 mEq/L/day.
    • Alcoholism
    • Malnutrition
    • Liver disease
    • Concomitant hypokalemia
  • Clinical Manifestations:
    • Clinical manifestations are typically delayed for 2-6 days after overly rapid elevation of serum Na
    • Symptoms are often irreversible and include dysarthria, dysphagia, paraparesis, quadriparesis, behavioral disturbances, movement disorders, seizures, lethargy, confusion, disorientation, obtundation, and coma
    • When hyponatremia is corrected (too quickly), the brain volume shrinks in response à this rapid fall in brain volume results in demyelination. Exactly how this occurs is not completely understood.



Evernote Link: https://www.evernote.com/shard/s338/sh/ef1c46f6-1ffd-4342-afb6-d0360d3fb651/2e36bca5e46d58e4c2b8c4cf1395b7dd


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