Osmotic demyelination syndrome (ODS), also called central pontine and extrapontine myelinolysis, is a condition caused by destruction of the myelin sheath surrounding nerves in the central nervous system. The damage is thought to be caused by rapid osmolar shifts in the central nervous system, leading to entry of water into brain cells and brain swelling, followed by volume loss from brain cells and cell death. It most commonly results from rapid correction of hyponatremia but can also be seen in patients with other electrolyte disturbances, malnutrition, severe burns, alcohol use disorder, renal failure, or liver disease. The pons is the part of the brain most commonly affected; however, other brain regions can also be involved.

Symptoms depend on the brain regions that are damaged but may include seizures, quadriparesis, hyperreflexia, pseudobulbar palsy, gaze paralysis, diplopia, dysphagia, dysarthria, tremor, ataxia, and altered mental status. There may be a bimodal presentation, with acute symptoms followed by several days of improvement and then subacute deterioration. Prognosis is variable and there is a risk of death or chronic disability.