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Central pontine myelinolysis



Nervous system


Central nervous system disorders
Central and peripheral nervous system disorders
Peripheral nervous system disorders
Autonomic nervous system disorders
Nervous system pathology review

Central pontine myelinolysis


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High Yield Notes
8 pages

Central pontine myelinolysis

8 flashcards

USMLE® Step 1 style questions USMLE

1 questions

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?

Image reproduced from Wikimedia Commons 

Memory Anchors and Partner Content
External References

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.

In addition to the neurons, there are also supporting cells called oligodendrocytes and astrocytes.

Oligodendrocytes physically wrap their fatty myelin-rich cell membranes around neuronal axons that are nearby to help action potentials move more quickly through them.

And astrocytes help repair damaged neurons.

Neurons and oligodendrocytes are very sensitive to changes in the amount of water and electrolytes in themselves and their environment.In other words, in the intracellular and extracellular compartment.

And the pons is a part of the brain that’s particularly sensitive.

The cell membrane is permeable to water, but some substances called osmolytes cannot cross over as easily and are called semi-permeable.

Examples of osmolytes are electrolytes like potassium, sodium, and chloride, as well as organic substances like phosphorylated glucose - which makes the molecule more polar and prevents it from slipping through the membrane easily.

Intracellularly, there is high potassium and low sodium, while extracellularly, there is high sodium and low potassium.

Normally, extracellular osmolality matches intracellular osmolality, meaning they are in equal balance of water and solute concentration.

When there’s a difference between the intracellular and extracellular osmolality, water flows towards the compartment with a higher osmolality to balance things out - and that’s osmosis - the process, not the company!


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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