Objective: To describe a case of levodopa responsive tremor due to osmotic demyelination as a result of severe hypernatremia

Background: Osmotic demyelination is a known complication of rapid correction of hyponatremia, but has also been reported with severe hypernatremia.  Rapid osmotic shifts can result in injury to astrocytes and oligodendroglia leading to a demyelination syndrome.  The most common location for osmotic demyelination to occur is the central pons (central pontine myelinolysis, CPM) but other brain regions (extrapontine myelinolysis, EPM) such as cerebellum, external capsule, striatum, thalamus, or hippocampus may also be involved [1].  Extrapyramidal movement disorders have been reported with EPM involving the striatum including levodopa responsive parkinsonism in an adult with EPM [2].  However, EPM is a rare phenomenon in children and to our knowledge this is the first report of levodopa responsive symptoms in a child with an osmotic demyelination syndrome.

Method: Case report

Results: The subject presented at the age of 16 months with encephalopathy and dehydration in the setting of an acute viral illness compounded with chronic malnutrition.  Labs on admission were notable for sodium of 198, potassium 2.5, chloride 153, osmolality 415.  MRI showed T2 hyperintensity of the central pons, thalami, cerebellar peduncles, external capsule, and corpus callosum.  Encephalopathy improved, electrolytes were slowly corrected, and the patient was discharged after 19 days.  Exam at that time was notable for axial hypotonia with mildly brisk reflexes in the lower extremities.  She was subsequently lost to follow up for a period of time, but was readmitted for malnutrition at the age of 29 months.  Action tremor was noted with reaching for objects and was exacerbated when upset.  Levodopa treatment was initiated at 5 mg/kg/day with subsequent improvement in the tremulous movements.  At follow up 3 months later, no rigidity, bradykinesia, or tremors were present on exam but remains non-ambulatory with two-hand support required for standing.

Conclusion: Extrapontine myelinolysis is a rare complication of osmotic shifts.  Extrapyramidal symptoms have been reported with extrapontine myelinolysis.  This is the first case of a levodopa responsive tremor in a child with extrapontine myelinolysis from severe hypernatremia.

References: [1] Martin RJ. J Neurol Neurosurg Psychiatry 2004;75(Suppl III):iii22–iii28. [2] Toft M & Dietrichs E. Movement Disorders 2011;26:2180-1.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/levodopa-responsive-tremor-in-a-young-child-as-a-delayed-complication-of-osmotic-demyelination-from-severe-hypernatremia/