Clinical meaning
Central pontine myelinolysis (CPM), now more accurately termed osmotic demyelination syndrome (ODS), results from overly rapid correction of chronic hyponatremia. In chronic hyponatremia (> 48 hours), brain cells adapt by extruding organic osmolytes (glutamate, taurine, myo-inositol, glycerophosphocholine) to prevent cerebral edema. When serum sodium is corrected too rapidly, the extracellular osmolality rises faster than brain cells can re-accumulate osmolytes, creating an osmotic gradient that draws water out of brain cells. Oligodendrocytes are particularly vulnerable to this osmotic stress, causing apoptosis and demyelination. The pons is most commonly affected (dense fiber tracts, watershed vascular zone), but extrapontine sites (basal ganglia, thalamus, cerebral white matter) occur in up to 50% of cases — hence the term ODS. Symptoms typically appear 2-6 days after sodium correction: initial improvement from hyponatremia correction is followed by new neurological deterioration (biphasic clinical course).
Diagnosis & workup
Diagnostics & workup: - MRI brain (GOLD STANDARD): T2/FLAIR hyperintensity in central pons ('trident' or 'piglet face' pattern sparing the periphery and ventrolateral pons); DWI positive early; extrapontine lesions in basal ganglia, thalami - MRI timing critical: may be NORMAL in first 2-4 days of symptoms; repeat MRI at 10-14 days if clinical suspicion remains high despite initial negative scan - Serial sodium monitoring: document rate of correction — Na+ rise should be < 8 mEq/L/24h (some guidelines say < 10; stricter limit < 6 in high-risk patients) - Clinical presentation: biphasic course — initial improvement from hyponatremia treatment, then new symptoms 2-6 days later: dysarthria, dysphagia, spastic quadriparesis, pseudobulbar palsy, 'locked-in syndrome' in severe cases - CT head: usually normal or may show subtle pontine hypodensity (much less sensitive than MRI) - EEG: may show encephalopathic pattern but non-specific - CSF: typically normal or mildly elevated protein; helps exclude infectious or inflammatory etiologies - Serum osmolality trending: confirms osmolarity changes that preceded symptoms