Extra pontine osmotic demyelination syndrome

Extra-pontine Myelinolysis After Rapid Correction of Hyponatremia Responding to Levodopa

Osmotic demyelinating disease of the central nervous system has two variants: central pontine myelinolysis and extra-pontine myelinolysis (EPM). Up to 10% of cases of osmotic demyelination syndrome are associated with EPM, which mostly affects the thalamus and basal ganglia. It is commonly associated with the rapid correction of hyponatremia. An elderly woman in her 60s presented with complaints of acute gastroenteritis and giddiness and visited the emergency ward. On examination, she was conscious and oriented to time but disoriented to place and person and had slurring of speech with signs of dehydration. Her serum sodium levels were 100 meq/L, and her brain MRI was normal. After shifting her to the intensive care unit, she was treated with 200 ml of 3% NaCl bolus to correct her hyponatremia. On day three, she began developing rigidity in both lower limbs, which progressed to the upper limbs with hyperreflexia and mutism. A brain MRI was done, which showed subtle hyperintensities in the caudate lobe with no other new findings. Her serum aldosterone and cortisol were on the lower side of the normal range. Treatment of tablet levodopa-carbidopa (100/25) combination thrice a day (TDS) led to an improvement in her health condition.

Osmotic Demyelination Syndrome - Evolution of Extrapontine Before Pontine Myelinolysis on Magnetic Resonance Imaging

Osmotic demyelination syndrome is a rare entity characterized by noninflammatory demyelination afflicting the central pons, basal ganglia, thalami, peripheral cortex, and hippocampi. Histopathologically, there is a destruction of myelin sheaths sparing the underlying neuronal axons due to the susceptibility of oligodendrocytes to rapid osmotic shifts often encountered in chronically debilitated patients. We present the temporal progression of signal abnormalities on sequential magnetic resonance imaging (MRI) scans in a middle-aged male initially presenting with altered mental status due to severe hyponatremia and subsequently developing rigidity, diagnosed as osmotic demyelination syndrome based on typical imaging findings and supportive laboratory parameters. This case demonstrates the importance of diffusion signal abnormalities as the first indicator of osmotic demyelination, evolution of extrapontine before pontine signal changes and the relative lack of correlation between patient's clinical profile and the extent of MRI signal abnormalities.