Objective: To report a case of osmotic demyelination syndrome (ODS) with continuing clinical and radiological worsening beyond its previously established temporal course.

Background: ODS is a known complication of rapid correction of hyponatremia. It may present either as Central pontine myelinolysis (CPM), Extra-pontine myelinolysis (EPM) or a combination of both. It has a biphasic clinical presentation with an initial phase of encephalopathy due to low sodium followed 1-7 days later by features of spastic quadriparesis, bulbar palsy, coma in CPM and extrapyramidal symptoms in EPM. Clinical and radiological evidence of ODS may begin 0.5-7 days after the initial insult but has been documented to occur even after 16 days. Radiological findings are known to lag behind the clinical manifestations and MRI may show features consistent with ODS only after a few weeks. We report a case with a protracted and delayed worsening of not only the radiological but also the clinical features well beyond the expected timeline of ODS.

Method: Nine days after initial hospitalization for hyponatremia, a 63-year-old male presented with clinical features of bradykinesia, rigidity and dysarthria which progressed over the next 7 days. MRI at day 9 was normal. On day 16, MRI showed diffusion restriction and FLAIR changes in the striatum. The patient had an almost static course for the next 2 weeks. In spite of no further sodium fluctuations, he then had worsening parkinsonism with dysphagia evolving into an akinetic rigid state. MRI at this point (day 30) showed new diffusion restriction with T2/FLAIR changes in bilateral thalamus as well as central pons. Possible etiologies considered were infective, metabolic, autoimmune or hypoxic.

Results: CSF analysis was unremarkable. Serum autoimmune and paraneoplastic encephalitis antibodies were negative. There was no history of hypoxia or carbon monoxide exposure. There was no evidence of metabolic abnormalities. PET-CT scan did not show any malignancy. The overall clinical background of evolving clinical and radiological features was concluded to be consistent with EPM followed by CPM. The patient improved with Levodopa with no adverse effects.

Conclusion: ODS despite being an age-old condition can continue to present in a unique manner and knowledge of this possible delayed pattern of presentation is important in clinical practice.

References: 1. de Souza A. Movement disorders and the osmotic demyelination syndrome. Parkinsonism Relat Disord. 2013 Aug;19(8):709-16.
2. Ruzek KA, Campeau NG, Miller GM. Early diagnosis of central pontine myelinolysis with diffusion-weighted imaging. AJNR Am J Neuroradiol. 2004 Feb;25(2):210-3.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/delayed-osmotic-demyelination-syndrome-an-evolving-spectrum/