MYELINOLYSIS – CPM AND EPM  CPM Stands for Central Pontine myelinolysis. EPM stands for ExtraPontine Myelinolysis.


Rapid correction of hyponatraemia, which developed slowly over weeks to months Can result in myelinolysis. This because brain cells adopt to slowly developing hypo osmolality by reducing intracellular osmolality to maintain normal volume. If under these conditions, rapid correction of hyponatraemia causes increase in extracellular osmolality can lead to the rapid shift of water out of neurons, this results in the sudden reduction of their volume and cause neurons to detach from their myelin sheaths. This is called as MYELINOLYSIS.

Mostly occurs in the pons. Hence known as Central pontine myelinolysis. If occurs outside pons known as Extrapontine myelinolysis.

Mechanism is same for both CPM and EPM. But clinical picture differs.

Clinical Picture: Usually patient present with Seizures or encephalopathy symptoms due to Hyponatraemia. Intially patient is normal on Correction of hyponatraemia. But after several days presents with any of the following complaints.


  1. Dysarthria and Dysphagia due to cortico bulbar tract involvement.
  2. Quadriparesis: initially flaccid paralysis (due to corticospinal tract involvement) then later Spastic paralysis (due to central pons involvement)
  3. Eye involvement present if tegmentum of pons involved.

EPM: Clinical picture depends on areas of involvement. But most commonly patient present with movement disorders.


Rate of Correction of Hyponatraemia in chronic and asymptomatic patients should not exceed 10mmol/L/day or even slower is Safer.        


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