What Is Central Pontine Myelinolysis?

Overview

Central Pontine Myelinolysis (CPM) is a condition that affects your brain by damaging the protective layer around the nerve cells called the myelin sheath. This damage often occurs in an area at the base of the brain called the pons. This part makes up your brainstem, which links the brain to the spinal cord and acts as the brain’s coordinator for breathing, consciousness and coordination. 

CPM is also called osmotic demyelination syndrome. This disorder happens when there is a rapid increase in your blood sodium level, which usually occurs after medical treatment for low sodium level (hyponatremia). This can lead to different symptoms associated with damage to the brain, like impaired cognitive function and movement disorders. 

CPM was previously considered fatal, but recent studies have shown that CPM has a survival rate of 94%.^1,2 

Most people make a full recovery, whilst others survive but live with disabilities. Rarely, CPM leads to death.

Causes of central pontine myelinolysis

The main cause of CPM is the rapid increase in sodium levels in the body, usually after injecting sodium solution into the bloodstream to correct low sodium levels.^1,3 

Sodium is an important electrolyte in your body. Its role is to maintain the balance of fluids inside and outside the cells. Therefore, sudden rises in sodium levels can cause water to move out of the brain cells, disrupting the balance and damaging the protective myelin sheath around nerve cells in the pons. This damage leads to the symptoms you see in patients with CPM. 

Other risk factors for developing CPM include the following:

• Excessive alcohol use
• Malnutrition 
• Liver disease
• Severe burns 
• Low potassium (hypokalemia)⁴
• Use of diuretics (medications that increase the production of urine)
• Hyperemesis gravidarum (severe nausea and vomiting during pregnancy) 

Signs and symptoms of central pontine myelinolysis

Symptoms of CPM generally develop over a period of two weeks after the correction of a low blood sodium level. Some of the symptoms of CPM include: 

• Decreased awareness or confusion
• Difficulty speaking or swallowing 
• Reduced thinking ability 
• Weakness or paralysis in limbs 
• Reduced sensation 
• Loss of balance or coordination 

In severe cases, CPM can cause: 

• ‘Locked in syndrome’ - a condition where all the muscles in your body are paralysed except your eye muscles⁵
• Coma 
• Death 

Some patients fully recover after a few weeks or months, while others sustain lifelong disabilities. Moreover, patients may develop additional symptoms over time, like behavioural impairments or movement disorders such as parkinsonism (a disorder presenting with slow movements, tremors, rigidity and unstable posture). 

In some cases, nerve cells in the brain outside of the pons can also be damaged, which is called extrapontine myelinolysis (EPM). This occurs in roughly 25% of patients with CPM.² Patients with EPM present with similar symptoms to CPM. 

Diagnosis

A diagnosis of CPM is made on the basis of relevant risk factors. These risk factors can include having a history of chronic alcoholism or liver transplant and relevant clinical history, such as a recent correction of a low blood sodium level. 

Healthcare providers will diagnose CPM by doing the following:⁷

• Asking questions about your symptoms and taking your medical history
• Performing a physical examination and a neurological assessment to look for signs and symptoms associated with CPM 
• Looking at your sodium level when you were treated and looking at how quickly your sodium was corrected. They may also look at other electrolytes, such as potassium 
• Performing a magnetic resonance imaging MRI scan to look for areas of the brain that may have been damaged by CPM. An MRI scan is a gold standard diagnostic test for CPM. In some cases, evidence of CPM cannot be seen on an MRI scan straight away, so another MRI scan is carried out 1-2 weeks after symptom onset 

Management and treatment for central pontine myelinolysis

No standard treatment is available for CPM.⁶ The treatment primarily focuses on symptom management. 

Methods of symptom management include:

• Ventilator support
• Physiotherapy and rehabilitation to regain muscle function
• Anti-parkinsonism drugs to treat tremors and rigidity
• Speech and language therapy

In some cases, reversing the high sodium level seen in CPM has been effective. This is done by lowering the sodium level and then slowly increasing it again. Currently, some experimental treatments are being explored. However, those that have shown positive outcomes have been trialled in small samples, making it difficult to generalise the results. 

Prognosis

The prognosis for patients with CPM is quite variable. Previously, CPM was thought to be a fatal condition, but recent research has shown the outcome of CPM to be much better. 

Despite the significant proportion of patients with poor outcomes of CPM, 40-73% of patients either partially or fully recover.

The worst outcome is seen in patients with liver transplants, severe hyponatremia, or patients with both hyponatremia and hypokalemia. Whereas, better outcomes are associated with milder cases of CPM and earlier detection. 

FAQs

How can I prevent central pontine myelinolysis?

The two key steps that can be taken to reduce the risk of CPM are controlling your sodium levels so that they do not become too low and ensuring that your healthcare provider effectively treats hyponatremia if it does arise.

If you have a medical condition that might lead to low sodium levels, be extra careful. Learning the signs of low sodium levels can enable you to identify and address them promptly.

The signs of low sodium level are: 

• Nausea and vomiting
• Headache, confusion or fatigue
• Low blood pressure 
• Low energy 
• Seizures or comas
• Restlessness and irritability 
• Muscle weakness, twitching or cramps 

Medical professionals can also prevent the development of CPM by following the guidelines that outline how to safely raise sodium levels, doing it in a way that does not cause sodium levels to rise too rapidly by administering it in small amounts.

If you are suffering from alcohol use disorder, cutting down alcohol consumption can reduce your risk of developing CPM.⁸ Healthcare providers can provide support in treatment of alcohol abuse disorder through behavioural therapy and medications, as well as by directing you to support groups. 

How common is central pontine myelinolysis?

CPM is a relatively rare neurological condition. The exact prevalence of CPM is unknown as mild cases tend to be asymptomatic and left undiagnosed. 

Who is at risk of central pontine myelinolysis?

Patients with a chronically low blood sodium level that lasts for over 48 hours are at higher risk of developing CPM.³ When your sodium level remains low for a long time, your body adapts to this condition. Consequently, if there is a sudden increase in sodium concentration, your body can't adapt quickly enough, which raises the risk of developing CPM.

Patients with a low sodium level due to other medical conditions, such as chronic alcohol use, malnutrition or following a liver transplant are also at high risk of developing CPM. 

Although a low sodium level (hyponatremia) is the most common cause of CPM, other electrolyte imbalances, such as low potassium (hypokalemia), can be a risk factor for developing CPM. 

When should I see a doctor?

As CPM is rare in the general population and most commonly found in clinical settings, there is no specific guideline of when to see a medical professional. However, if you suspect you have CPM, you should seek medical attention promptly. You should consider seeing a doctor if you have the following signs: 

• Rapid onset of neurological (brain related) symptoms, like difficulty speaking or swallowing, weakness in your arms or legs, and impaired coordination 
• If you have recently had correction of low sodium levels and begin experiencing symptoms  
• If you have any risk factors for CPM, such as alcohol use disorder, malnutrition or have undergone a recent liver transplant

Summary

Central pontine myelinolysis, also known as osmotic demyelination syndrome, is a condition that results in neurological symptoms affecting cognition and movement. It occurs as a result of a rapid medical correction of low sodium levels, which causes damage to the protective myelin sheath around nerve cells in the brain. CPM can be diagnosed by reviewing a patient’s history, looking at a patient’s sodium level and doing an MRI scan. Treatment of CPM is primarily focused on prevention and symptom management, but CPM can also be treated by reversing the rapid correction of hyponatremia. Overall, the survival rate of CPM is higher than previously expected, but patients who survive may suffer from lifelong disabilities. CPM can be prevented through educating and treating individuals at risk of low sodium level and ensuring that the sodium level is increased at an appropriate rate.