Hypsarrhythmia is an abnormal pattern that appears on an EEG test. This pattern shows up as a specific and recognizable pattern of tall, wide waves on top of the background.

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An electroencephalogram (EEG) is a highly specialized test that can detect a pattern of electrical activity in your brain. When there is a pattern of high amplitude waves superimposed on an irregular background, that’s defined as hypsarrhythmia.

Nerve activity in the brain can be detected by metal leads placed superficially on the scalp, and the rhythm and intensity of the electrical nerve impulses are then translated by a computer to produce a wave pattern. That reflects the intensity and duration of the rhythm.

The height and timing of the waves are read by a specialized neurologist. This data can be used to diagnose certain issues affecting the brain.

This article explores what hypsarrhythmia might look like on an EEG, what types of conditions this result might signal, and what to expect when hypsarrhythmia is noted on your test.

Hypsarrhythmia is a pattern that appears on an EEG and is linked to certain neurodevelopmental epilepsy syndromes.

The pattern features wide and tall waves, along with several areas of spikes. This can indicate several areas of the brain where seizures begin.

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An EEG typically uses dozens of electrodes placed on various areas of your scalp. Each electrode is placed to detect the nerve impulses in a general region of the brain, and this may be correlated to how these areas of the brain function.

Electrodes are usually labeled with a combination of letters and numbers, with the letters indicating a different section or lobe of the brain:

  • F: frontal
  • Fp: frontopolar
  • T: temporal
  • C: central
  • P: parietal
  • O: occipital
  • A: auricular (ear electrode)

Arrhythmia means an irregular heart rate or rhythm. There are several defined patterns, such as atrial flutter and ventricular fibrillation.

An EEG normally shows a pattern of waves. Some conditions, like a stroke or head trauma, could cause brain waves to slow down in certain areas. Other issues, like seizures, can cause these waves to increase in size, strength, or frequency, or take on an irregular pattern.

Reading an EEG takes specialized training, but a neurologist can use the patterns recorded on your EEG to help identify damaged areas in the brain.

The electrode where the abnormal activity happens will correspond with a general area of your brain, or may show where a seizure that happens in one area of the brain originated.

While an EEG can be done while someone is having a seizure, it is typically done between seizures because it can otherwise be difficult to detect what’s happening in the brain. This is known as an interictal EEG.

In the case of hypsarrythmia, certain EEG alterations are noted both during and between seizures. Having abnormalities between seizures can be a sign of many different serious epilepsy syndromes of infancy and childhood, and it is a common feature of West syndrome.

What is West syndrome?

West syndrome is a condition that involves infantile spasms, a pattern of hypsarrthymia on an EEG, and neurodevelopmental issues that begin in early infancy. This condition often appears in the first year of life, with the most common age of onset being 6 months.

The spasms that occur with West syndrome are believed to be the result of uncontrolled nerve transmissions in the brain. They can last anywhere from a few seconds to clusters that continue for 10 or 20 minutes.

Severity of these spasms can vary from person to person. In infants, these spasms often happen shortly after waking up or after a feeding.

The hypsarrythmia patterns that appear with West syndrome aren’t fully understood by researchers at this time.

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Not every infant who experiences these spasms will have long-term epilepsy. About a third of all children with West syndrome have recurrent epileptic seizures later in life.

West syndrome may also develop into other conditions with spasms or intellectual disability, such as Lennox-Gastaut Syndrome.

Anticonvulsant medications can help manage spasms in infants and children. Other medications that have shown improvements in managing these spasms include:

While there are guidelines for the management of West syndrome, infantile spasms, and symptomatic hypsarrythmia, treatment is highly individualized.

West syndrome is a rare condition, affecting about 0.31 out of every 1,000 live births in the United States. However, it accounts for about 30% of all cases of epilepsy in infancy.

Although a third of infants with this condition will have recurring seizures as they age, others may have isolated spasms at an older age. Another third of infants with West syndrome will see their spasms disappear in time.

Many infants with EEGs that show hypsarrythmia will be diagnosed with a serious epileptic condition like West syndrome. They may experience seizures or spasms and developmental delays as they age.

Talk with your healthcare team if you or your baby experience spasms and have not been diagnosed with a seizure disorder. Your doctor might order an EEG if they are concerned that your spasms could be related to epilepsy.