= CENTRAL PONTINE MYELINOLYSIS= OSMOTIC MYELINOLYSIS

Predisposed: chronic alcoholic with liver failure (60–70%); malnourished patient; chronically debilitated transplant recipient (liver transplantation with cyclosporine use); prolonged use of diuretics; extensive burns

Etiology: unknown; comatose patient receiving rapid correction / overcorrection of severe hyponatremia >12 mmol/L/d (following prolonged IV fluid administration)

Pathophysiology:

rapid correction of sodium → release of myelinotoxic compounds by gray matter components → destruction of myelin sheaths of oligodendrocytes (osmotic myelinolysis with intramyelinitic splitting, vacuolization, rupture of myelin sheath); preservation of neurons + axons

Histo: abundant foamy histiocytes without lymphocytes / neutrophils; luxol fast blue staining demarcates demyelination; neurofilament staining shows preserved neuronal axons

Age: middle age; M >F

• spastic quadriplegia + pseudobulbar palsy (= head and neck weakness, dysphagia, dysarthria)
• encephalopathy with seizures + acute mental status change
• progression to pseudocoma (locked-in syndrome) in 3–5 days
• serial measurements of serum sodium

Location:

1. isolated pons lesion (most commonly)
2. combined type = central pons + extrapontine areas: globus pallidus, putamen, thalamus, cerebellar white matter, lateral geniculate body, caudate nucleus, subcortical cerebral white matter, corona radiata, hippocampi

typically spared: ventrolateral pons; pontine portion of corticospinal tract

CT:

• diminished attenuation in central basilar region of pons without mass effect
• hypoattenuated areas in basal ganglia + thalamus

MR (positive 1–2 weeks post-onset of symptoms):

• single central symmetric midline pons lesion:
  • hyperintense symmetric trident-shaped / round (coronal scan) + bat-wing configuration (sagittal scan) on T2WI + FLAIR
  • hypointense / (less commonly) isointense on T1WI
  • sparing of ventrolateral pons + pontine portions of corticospinal tracts
• bilateral symmetric well-demarcated lesions in basal ganglia ± other extrapontine sites
• ± restricted diffusion (24 hours after onset of symptoms)
• no enhancement of lesions

Prognosis: 5–10% survival rate beyond 6 months; significant neurologic sequelae (in most)

DDx: hypoxia, Leigh disease, Wilson disease