We report a case of a 43-year-old woman who developed osmotic demyelination syndrome following correction of extreme hyponatremia that was considered to be of chronic nature. The serum sodium level was 91 mmol/L on admission to hospital. It was decided to correct the serum sodium slowly and the goal was to keep the rate of correction below 12 mmol/l per 24 hours. This was achieved during the first two days of treatment but during the third day the rise in serum sodium was 13 mmol/l. On the 11th day of admission the patient had developed manifestations of pseudobulbar palsy and spastic quadriparesis. Magnetic resonance imaging study confirmed central and extrapontine myelonolysis. The patient received supportive therapy and eventually made full recovery. Current concepts in the pathophysiology of osmotic demyelination syndrome and the treatment of hyponatremia are reviewed. We recommend that the rate of correction of chronic hyponatremia should not exceed 8 mmol/l per 24 hours.

Key words: Central pontine myelinolysis, cerebral adaptation, hyponatremia, osmotic demyelination syndrome.

 

Table I. Laboratory tests on admission to hospital.

Blood tests

Variable Result Normal reference range

White blood cells 12.0 x10E9/L 4.0-10.5 x10E9/L

Hemoglobin 122 g/L 118-152 g/L

Platelets 320 x109/L 150-400 x109/L

Sodium 91 mmol/L 136-145 mmol/L

Potassium 4.3 mmol/L 3.5-5.0 mmol/L

Chloride 58 mmol/L 98-110 mmol/L

Bicarbonate 18 mmol/L 22-31 mmol/L

Calcium 1.97 mmol/L 2.20-2.60 mmol/L

Phosphate 0.53 mmol/L 0.8-1.6 mmol/L

Urea 4.1 mmol/L 2.5-8.5 mmol/L

Creatinine 50 mmol/L 60-100 mmol/L

Glucose 10.7 mmol/L 4.0-10.0 mmol/L

Albumin 41 g/L 36-51 g/L

Osmolality 194 mOsm/kg 280-300 mOsm/kg

TSH 0.362 mU/L 0.4-4.0 mU/L

Free T4 37.6 pmol/L 10-25 pmol/L

Urine tests

Osmolality 187 mOsm/kg -

Sodium 79 mmol/L -

 

Abbreviatons: TSH, thyrotropine; T4, thyroxine.

 

Figure 1. Time course of the serum sodium concentration over the first nine days of hospitalization.

Figure 2. Magnetic resonance imaging of the brain.

a. T2-weighted image obtained on the eight hospital day showing no abnormalities.

b. T2-weighted image obtained on the 15th hospital day showing a symmetrical area of increased signal intensity in the center of the pons (arrow), characteristic of central pontine myelinolysis.

c. FLAIR* image obtained on the eight hospital day was initially considered unremarkable but in retrospect a mild hyperintense signal can be detected in the caudate nucleus bilaterally (arrows).

d. FLAIR* image obtained on the 15th hospital day showing symmetrical high intensity alterations in the in the caudate nucleus and basal ganglia (arrows), consistent with extrapontine myelinolysis.

*FLAIR: Fluid Attenuated Inversion Recovery.