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EEG and Encephalopathy

The Electroencephalogram or EEG is a useful tool in the diagnosis of encephalopathy and the variety of causes that can lead to this diagnosis.

Keep reading below for a brief summary of types and their possible causes.


Developmental and epileptic encephalopathies are a group of several neurodevelopmental disorders often characterized by early-onset seizures, specific EEG abnormalities, and developmental delays or regression. These encephalopathies are classically considered pediatric disorders because of their onset but because of advances and supportive treatments, many patients survive into adulthood and exhibit unique abnormalities not often seen in children.

But first - what is encephalopathy?


The word encephalopathy describes basically any disease that affects the whole brain and alters its structure or how it works. Changes in mental function are then the result.


The most common symptom of encephalopathy is a change in mental state, with problems such as:

  • loss of memory

  • reduced ability to think clearly or concentrate

  • drowsiness

  • changes in personality such as irritability, aggression, or impulsive behaviour

Some people might also have:

  • involuntary muscle twitching

  • difficulty speaking

  • difficulty swallowing

  • unusual eye movements

  • tremor

  • muscle weakness

  • seizures

  • dementia

  • loss of consciousness


There are several different patterns of encephalopathy.

Some people have acute encephalopathy, which comes on fairly quickly and can go away. Others have chronic encephalopathy, which tends to develop slowly and does not go away.


Some people with chronic underlying conditions, such as liver disease, can be well at times and then have an episode of encephalopathy triggered by an infection, bleeding in the digestive tract, alcohol, medications, or an electrolyte imbalance.


Some encephalopathies cause permanent damage to the brain, while others do not. And of course, some can be fatal.

Encephalopathy is not a single disease; it can have a wide range of underlying causes.


There are many types of encephalopathy, including:

  • Hepatic encephalopathy — a problem with the liver causes a build-up of toxic substances that the liver normally removes. These toxic substances then disturb the normal functioning of the brain. Hepatic encephalopathy can be caused by a chronic liver condition such as cirrosis, an infection, overdose of prescription medications, or bleeding in the digestive tract.


  • Hypoxic-ischaemic encephalopathy — lack of oxygen to the brain leads to abnormal brain function. This can be caused by heavy bleeding, near-drowning or near-suffocation.



  • Chronic traumatic encephalopathy (CTE) — this is probably caused by repeated blows to the head and concussions. It is associated with contact sports such as boxing and football.


  • Wernicke Encephalopathy — a severe deficiency of a B vitamin called thiamine causes the encephalopathy. It occurs most commonly in people with severe alcoholism.


  • Metabolic encephalopathy. This happens when another health condition, such as diabetes, liver disease, kidney failure, or heart failure, makes it hard for the brain to work. For example, if blood sugar gets too high in diabetes, it can lead to confusion and even a coma.


  • Hashimoto’s Encephalopathy. This type is linked to a thyroid condition called Hashimoto’s disease. The cause isn’t clear, but it may be that your immune system attacks your brain and changes the way it works. Fun fact: our thyroid gland is shaped like a butterfly.



  • Infections of the brain, such as encephalitis or meningitis, or in another part of the body, such as a urinary tract infection. An extreme response to an infection, called sepsis, can also lead to encephalopathy.


Encephalopathy can also be caused by:

  • autoimmune disorders

  • brain tumor

  • exposure to toxic substances such as alcohol, paints, solvents or radiation

And one we are very familiar with:

  • Nonconvulsive status epilepticus.



A patients outlook depends largely on whether the encephalopathy is reversible or irreversible.


  • Encephalopathy from head injuries, toxins, cardiac arrest, or lack of oxygen to the brain causes physical damage to the brain that is usually permanent and often irreversible.

  • In reversible encephalopathy, such as from organ failure, metabolic conditions, or infections, symptoms usually go away when they fix the problem that’s causing them. For example, for hepatic encephalopathy, clearing toxins from the blood can fix any issues with confusion, memory problems, or mood swings.


Now let's discuss the EEG:

What does metabolic encephalopathy show on EEG?


Common principles of EEG changes in metabolic encephalopathy are (1) varied degrees of slowing, (2) assorted mixtures of epileptic discharge, (3) high incidence of triphasic waves, and (4), as a rule, reversibility after treatment of underlying causes.




Slowing




Epileptic discharges



Triphasic waves


Triphasic waves classically are associated with hepatic encephalopathy. However, they are not specific and can be observed in other types of metabolic encephalopathies.


More on EEG encephalopathic findings:

Generalized slowing: This is the most common finding in diffuse encephalopathies.


Generalized slowing can be divided in a clinically useful way into 3 patterns: background slowing, intermittent slowing, and generalized slowing.


More specifically for Continuous slowing:

Polymorphic delta activity (PDA) occupies more than 80% of the record. This is usually unreactive, and a posterior dominant background is usually absent.



Polymorphic delta activity (PDA)


Essentially, the 3 levels of slowing described above represent 3 degrees of severity (ie, mild, moderate, and severe) of diffuse encephalopathy.


Some less common patterns:

These include alpha coma, beta coma, spindle coma



Alpha coma





Beta come




Spindle coma


Alpha coma, beta coma, and spindle coma are infrequent. Anoxia often is associated with alpha coma and drugs with beta coma. They are generally indicative of a severe degree of encephalopathy and reactivity is a good prognostic factor.


More severe patterns:

These patterns are generally considered the next level of severity beyond generalized slowing. They include periodic patterns (such as burst-suppression), background suppression, and electrocerebral inactivity (ECI).



Burst suppression


Electrocerebral inactivity (ECI)


So in closing - a Key Point to note:

Encephalopathy does not refer to a single disease but instead to a syndrome of overall brain disfunction. A syndrome that has many possible causes.

And as you can see encephalopathy entails a wide range of EEG changes.


No matter how long one has been in this field there are always going to be those ‘hard cases’ that stump us. Actually that’s part of what makes this field so interesting!


When presented with those scenarios it’s important to take a step back and ask the question - what are we looking for?


Are there changes in the background?


And when you see the changes go back to what you know. It will help you figure out what you don’t.


Roya Tompkins, MS, R EEG/EP T, RPSGT



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