Central pontine myelinolysis


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Central pontine myelinolysis

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Central pontine myelinolysis


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Central pontine myelinolysis

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USMLE® Step 1 style questions USMLE

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A 63-year-old woman is brought to the emergency department by her partner due to progressive lethargy and confusion. The patient was recently diagnosed with metastatic small cell carcinoma of the lung and has refused all treatment, wishing to pursue only “comfort care measures.” She has been smoking a pack of cigarettes per day for the last 45 years. Vital signs are within normal limits. Physical examination shows no abnormalities. Serum studies show the following:  
 Laboratory value  Result 
 Sodium   108 mEq/L 
 Potassium   4.2 mEq/L 
 Chloride   95 mEq/L 
 Creatinine   0.9 mg/dL 
 Albumin   3.2 g/dL 

The patient is started on hypertonic saline. On the second day of treatment, the partner notices the patient is unable to move, but she is able to blink in response to questions. Which of the following is the most likely location of the brain lesion in this patient?

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Central pontine myelinolysis p. 542


osmotic demyelination syndrome p. 542

Dysarthria p. 533

osmotic demyelination syndrome p. 542


osmotic demyelination syndrome p. 542

“Locked-in” syndrome

osmotic demyelination syndrome p. 542

Osmotic demyelination syndrome p. 542

SIADH and p. 351



Samantha McBundy, MFA, CMI

Gil McIntire

Tanner Marshall, MS

In central pontine myelinolysis, pontine refers to the pons of the brainstem, myelin refers to the fatty layer of insulation that wraps around neurons, and -lysis refers to destruction.

So, central pontine myelinolysis is the destruction of the myelin sheath around nerve cells that are in the pons.

The main cause of destruction is rapid osmotic changes, meaning that a lot of water leaves the cells, and dries them out, causing them to die.

So the other name for central pontine myelinolysis is osmotic demyelination syndrome.

Taking a look at the brain, the pons is part of the brainstem and it’s nestled between the midbrain and the medulla oblongata.

The pons itself has control centers that help manage the respiration rate and the depth of breathing while we’re awake and when we sleep. So if you try to take a deep breath right now - that’s your pons in action!

Neuron clusters or nuclei for cranial nerves V: trigeminal, VI: abducens, VII: facial, and VIII: vestibulocochlear are also housed in the pons.

Cranial nerve V allows you to feel things on your face and controls the muscles that help you chew, bite, and swallow.

Cranial nerve VI allows your eyes to move side to side.

Cranial nerve VII helps with facial expressions - like making a weird face, and cranial nerve VIII helps with hearing.

All of these nerves are made up of lots of individual neurons which capture signals from their dendrites, and pass those signals along through their axons.


Central pontine myelinolysis (CPM) is a neurological disorder caused by the rapid correction of hyponatremia. CPM is a demyelinating disease that damages the insulation around nerve fibers (called myelin). This damage disrupts the conduction of nerve impulses, leading to neurologic deficits.

Symptoms of CPM include muscle weakness, difficulty swallowing, and problems with speech, vision, and balance. These symptoms often occur suddenly and progress rapidly. Death from respiratory failure can occur within days or weeks of onset.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Central Pontine and Extrapontine Myelinolysis After Alcohol Withdrawal: Fig. 1" Alcohol and Alcoholism (2008)
  6. "Axonal damage: a key predictor of outcome in human CNS diseases" Brain (2003)
  7. "Clinical practice guideline on diagnosis and treatment of hyponatraemia" European Journal of Endocrinology (2014)

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