Features:
(1) history of hyponatremia, often with rapid sodium replacement
(2) clinical findings compatible with the site of involvement
(3) onset several days after correction of the hyponatremia
(4) MRI shows an increased signal in the area of involvement, usually symmetrical (CT scans are often negative)
Sites of involvement:
(1) pons: central pontine myelinolysis
(2) medulla oblongata, midbrain, pontine tegmentum: extrapontine myelinolysis
Symptoms with pontine involvement:
(1) mutism and dysarthria
(2) lethargy and affective change
(3) spastic quadriparesis
(4) pseudobulbar palsy
Symptoms in extrapontine myelinolysis:
(1) pupillary and oculomotor abnormalities (midbrain)
(2) depressed level of consciousness and cranial nerve signs (pontine tegmentum)
(3) ataxia
(4) movement disorders (parkisonian, dystonia, other)
Affected patients may die, suffer late sequelae, or make a complete recovery.
Differential diagnosis:
(1) psychiatric illness
(2) encephalitis associated with hyponatremia
(3) alcoholic withdrawal
