Understanding D/EE-SWAS: The Core Definition

Receiving a diagnosis of a rare epilepsy syndrome is overwhelming, especially when the names used to describe it seem to change every time you speak with a professional. This page is designed to help you navigate the confusing terminology and understand the core of what is happening in your child’s brain.

One Condition, Many Names

For decades, doctors have used different terms to describe the same phenomenon: a child whose brain shows intense electrical activity during sleep, leading to a loss of skills. While these terms are sometimes used interchangeably, they describe distinct aspects of the condition and usage is not fully uniform:

• CSWS (Continuous Spikes and Waves during Sleep): Historically, this term often referred to the clinical syndrome—the combination of the EEG pattern and the loss of skills ^[1][2].
• ESES (Encephalopathy with Status Epilepticus during Sleep): This term was frequently used to describe the specific “busy” pattern seen on the EEG (electroencephalogram, a test that records brain waves) ^[1].
• D/EE-SWAS (Developmental and/or Epileptic Encephalopathy with Spike-Wave Activation in Sleep): This is the modern, official name introduced by the International League Against Epilepsy (ILAE) ^[2]. It was created to be more precise and to emphasize that the condition is a “spectrum” rather than a single fixed point ^[3].

Understanding the D/EE-SWAS Spectrum

The new name, D/EE-SWAS, is broken down into two categories based on a child’s history before the condition began. This distinction provides a clinical framework to help doctors better understand the “baseline” and set appropriate goals for treatment ^[4].

1. EE-SWAS (Epileptic Encephalopathy with SWAS): This term is used when a child’s development was initially typical before the onset of the syndrome ^[4][5].
2. DEE-SWAS (Developmental and Epileptic Encephalopathy with SWAS): This term is used when a child already had a pre-existing neurodevelopmental disorder (such as a global developmental delay or a known genetic condition) before the sleep-related brain activity caused further deterioration ^[4][5].

The Hallmark: Regression and Stagnation

The most distressing part of this condition for parents is regression—the loss of skills a child once had. This is the defining clinical feature of the syndrome ^[3].

Regression can look different for every child. It may involve:

• Language: Losing the ability to speak in sentences or follow directions ^[3].
• Cognition: A decline in problem-solving skills or a “foggy” mental state.
• Behavior: New or worsening aggression, hyperactivity, or features of autism ^[6].
• Motor Skills: Becoming clumsy or losing fine motor control ^[3].

In some cases, a child may experience stagnation, where they simply stop learning new things or “plateau” while their peers continue to advance ^[3]. This regression is often “temporally linked” to the brain activity, meaning the skills start to fade around the same time the EEG patterns become more intense during sleep ^[3][7].

Why Is This Happening During Sleep?

It is counterintuitive that brain activity during sleep can affect a child’s waking life so profoundly. While research is ongoing, scientists hypothesize that these intense electrical discharges (spikes and waves) may interfere with the brain’s nighttime processing ^[8].

During normal sleep, the brain performs synaptic homeostasis—a proposed mechanism of pruning and strengthening connections to help with memory and learning ^[8]. In D/EE-SWAS, the constant electrical activity might block thalamocortical sleep spindles, which are believed to be essential for turning short-term memories into long-term ones ^[9]. The prevailing theory is that the “electrical noise” during the night prevents the brain from “saving” the day’s work, leading to the loss of skills over time ^[9][10]. However, the exact biological mechanisms remain an active area of research.

The “Spike-Wave Index” (SWI)

You may hear your doctor mention a “Spike-Wave Index” or SWI. This is a percentage that describes how much of the sleep period is occupied by these abnormal electrical discharges.

While there is no single “magic number” that definitively defines the diagnosis, many doctors look for an SWI where discharges occupy a significant portion of NREM (Non-Rapid Eye Movement) sleep ^[11]. Common historical thresholds include an SWI of over 85%, or over 50% if the child is showing clear signs of regression ^[11][12]. These are historical or study-specific thresholds, and there is no universally accepted minimum cutoff. SWI definitions and calculation methods vary substantially between laboratories. The SWI is just one piece of the puzzle; doctors must also interpret it alongside the child’s behavior, developmental history, and the “shape” of the brain waves ^[13].

A Rare Challenge

It is important to know that D/EE-SWAS is very rare, estimated to affect only 0.2% to 1.3% of children with epilepsy ^[4][11]. Because it is so uncommon, many general pediatricians or even local neurologists may have limited experience treating it. Finding a specialized pediatric epilepsy center can be an important step in ensuring your child receives the most current, evidence-based care.