A 34–year–old female presented with a 1–week history of dysarthria, ataxia and postural instability. The week prior to her presentation she was admitted to a local hospital with significant vomiting and dehydration. She was found to be hyponatremia with a sodium level of 110 mmol/L. Initially, she was treated with antiemetics for her nausea and vomiting and with hypertonic saline for her hyponatremia. However, her serum sodium levels did not improve with the this management and so she was initiated on Tolvaptan (vasopressin V2 receptor antagonist) therapy. On the subsequent day, her serum sodium level had increased to 145 mmol/L. Her overall condition improved and she was discharged in a stable condition. Five days later, she presented to our hospital with slurred speech, verbal stuttering, dysnomia, neologism, dysdiadokinesia, and dizziness. On physical exam, she had dysarthria and ataxia. The rest of her general and neurologic examination were normal. Her blood chemistry results were unremarkable with a normal sodium level. A CT scan of the brain done was negative for any acute pathology. This was later followed by a T2–weighted MRI (Figure 1) and FLAIR (Figure 2) that showed bilateral symmetrical hyperintensities in the Putamen area (red arrow) and Caudate nucleus (yellow arrow) with sparing of Globus Pallidus (green arrow). Discussion: The rapid correction of the patient’s severe hyponatremia using Tolvaptan and hypertonic saline along with the patient’s clinical presentation and MRI findings, all suggest that extrapontine myeleinosis is the most likely diagnosis. Extrapontine myelinosis (EPM) is a variant of Osmotic Demelination Syndrome (ODS). Rapid correction of severe hyponatremia (>12 meq/dl in 24 hours) can lead to osmotic demyelination syndrome. This was formerly referred to as central pontine myelinolysis, since demyelination does not necessarily involve the pons and may be more diffuse. Involvement of the basal ganglia with sparing of the pons is characteristic for EPM, which has been described in 10% of patients with ODS. The clinical manifestation of ODS can be delayed upto 2–6 days after rapid correction of the serum sodium. In our patient, clinical and MRI features of pontine involvement were absent. Positive findings included dysarthria and ataxia may be attributed to striatal dysfunction. These findings have been reported in isolated cases of EPM. On MRI, extrapontine changes have been described in the basal ganglia, cerebellum and white matter. Typically pallidal sparing is seen.
There is no proven effective therapy for ODS or EPM. In view of the typically severe and potentially permanent adverse consequences of ODS, prevention is essential. Among patients with hyponatremia, it is important to avoid overly rapid correction: rate of correction should be less than 10 meq/L in the first 24 hours and less than 18 meq/L in the first 48 hours.
Figure 1T2–weighted MRI showing bilateral symmetrical hyperintensities in the Putamen area (red arrow) and Caudate nucleus (yellow arrow) with sparing of Globus Pallidus (green arrow).
Figure 2FLAIR showing bilateral symmetrical hyperintensities in the Putamen area (red arrow) and Caudate nucleus (yellow arrow) with sparing of Globus Pallidus (green arrow).