Osmotic myelinolysis: Does extrapontine myelinolysis precede central pontine myelinolysis? Report of two cases and review of literature.

Osmotic myelinolysis is an acute, rare, demyelinating process. After the initial description of the condition by Adam and colleagues in 1959, many case series have been published describing the central and extrapontine myelinolysis. Imaging has a definitive role in establishing the diagnosis of osmotic myelinolysis in vivo and diffusion-weighted imaging reveals earliest changes in affected brain parenchyma. We report two cases of patients with proven malignancy who developed extrapontine myelinolysis after treatment for hyponatremia and progressed to central pontine myelinolysis within a week. This was confirmed with magnetic resonance (MR) imaging and clinical assessment. This temporal progression of MR features, especially on diffusion-weighted imaging, from extrapontine to central pontine myelinolysis in osmotic injury has not been described in literature to the best of our knowledge. An early MRI of the brain in suspected/high-risk cases of osmotic myelinolysis may show features of extrapontine myelinolysis in the form of restricted diffusion in bilateral basal ganglia and may serve as a guide for predicting progression, prognosticating and deciding further treatment of pontine myelinolysis. We propose that in a significant number of cases, central pontine myelinolysis may be predicted by doing an early MRI of the brain with diffusion-weighted imaging, when extrapontine symptoms start to develop. This can potentially increase the window period and possibilities for therapeutic intervention and may even help in prevention.