Osmotic Demyelination Syndrome

A 46 year old male with hyponatremia, altered level of consciousness, and seizures. What is the diagnosis? • Xray of the Week

Figure 1. Brain CT. What is the significant finding.

Figure 2.

A: Axial CT image obtained at the level of the 4th ventricle shows a centrally located region of low attenuation within the pons (red arrow).

B: Midline sagittal CT image shows a centrally located region of low attenuation within the pons (red arrow).

Discussion:

Osmotic demyelination syndrome (ODS) is a symmetric, non-inflammatory condition where the myelin fibers are disrupted primarily in the pons. The neuronal cell bodies and axons in the pons are preserved as well as the peripheral fibers and axons of the corticospinal tract (1). This syndrome was previously referred to as central pontine myelinolysis, but early detection of this condition showed that extrapontine structures can be involved. Other common structures include cerebellum and the lateral geniculate body (3). This condition occurs because of electrolyte abnormalities, especially hyponatremia, being corrected too rapidly with patients deteriorating within 2-8 days. Symptoms are based on which tracts are affected in the brain: Corticobulbar involvement will cause dysarthria and dysphagia; corticospinal tract involvement will cause flaccid paralysis and possibly spastic quadriparesis depending on basis pontis damage. Widespread pontine damage can cause “locked-in” syndrome (5). Extrapontine symptoms such as psychiatric disorders, movement disorders, depression, and seizures (1) may also occur.

Imaging findings in ODS can be delayed up to 2 weeks (2). Diffusion weighted MRI is recognized as the earliest and most sensitive imaging modality for ODS and is recommended to be performed on the initial day of symptoms (5). Characteristic MR findings include the symmetric trident pattern on T2-weighted and FLAIR MR images (2). T1-weighted images will show decreased signal intensity in affected areas with no mass effect; however findings on T1-weighted images are nonspecific (2, 4, 5, 6). MRI will not show demyelination of the ventrolateral pons and the pontine portion of the corticospinal tracts. CT scans are not the first line imaging study for ODS but can demonstrate regions of demyelination as low attenuation lesions in the basilar part of the pons without mass effect (Figs.1,2). Hypoattenuation can be seen in other parts of the brain such as the basal ganglia and thalamus and sparing of the pontine tegmentum (1,2). Lack of radiological findings does not rule out ODS.

To prevent the devastating complications of ODS, sodium levels must be gradually corrected depending on the initial lab value and symptoms. The goal of patients with sodium levels above 120 is to first achieve euvolemic status and then balance the electrolyte levels. They must be monitored and may be treated with vasopressin antagonists. Patients with severe hyponatremia (Na <120) or neurological symptoms can be given hypertonic saline (4).

References:

1. Alleman AM. Osmotic demyelination syndrome: central pontine myelinolysis and extrapontine myelinolysis. Semin Ultrasound CT MR. 2014;35(2):153-159. doi:10.1053/j.sult.2013.09.009

2. Howard SA, Barletta JA, Klufas RA, Saad A, De Girolami U. Best cases from the AFIP: osmotic demyelination syndrome. Radiographics. 2009;29(3):933-938. doi:10.1148/rg.293085151

3. Kleinschmidt-Demasters BK, Rojiani AM, Filley CM. Central and extrapontine myelinolysis: then...and now. J Neuropathol Exp Neurol. 2006;65(1):1-11. doi:10.1097/01.jnen.0000196131.72302.68

4. Lambeck J, Hieber M, Dreßing A, Niesen WD. Central Pontine Myelinosis and Osmotic Demyelination Syndrome. Dtsch Arztebl Int. 2019;116(35-36):600-606. doi:10.3238/arztebl.2019.0600

5. Ruzek KA, Campeau NG, Miller GM. Early diagnosis of central pontine myelinolysis with diffusion-weighted imaging. AJNR Am J Neuroradiol. 2004;25(2):210-213. http://www.ajnr.org/content/25/2/210.abstract

6. Yuh WT, Simonson TM, D'Alessandro MP, Smith KS, Hunsicker LG. Temporal changes of MR findings in central pontine myelinolysis. AJNR Am J Neuroradiol. 1995;16(4 Suppl):975-977. http://www.ajnr.org/content/16/4/975.abstract

Austin Sanu is a 3rd year medical student at the New York Institute of Technology College of Osteopathic Medicine. He plans on pursuing a residency in Diagnostic Radiology. Austin discovered his passion for radiology during his clinical rotations and finds using imaging to diagnose patients very rewarding. During his medical school career, Austin is a clinic manager for NYITCOM’s Community Free Clinic in Central Islip, Old Westbury, and Harlem. This organization helps patients without insurance receive health care while letting medical students get hands on experience before clinical rotations. Austin graduated from the New York Institute of Technology in 2017 with a Bachelor of Science degree in Biology. Austin’s hobbies include weightlifting and playing sports, especially basketball.

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Kevin M. Rice, MD is the president of Global Radiology CME

Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator.

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