Sonata polysomnography system expanded.

The modern Sonata polysomnography system is known for its versatility and high technical standard. Its 76 channels already enable a wide range of sophisticated applications.

The new 10-20 neuro module expands the Sonata system to 21 EEG channels, thereby meeting the requirements of the internationally standardized 10-20 EEG system. The 10-20 EEG system is a standardized and internationally recognized system for the placement of electrodes in electroencephalography (EEG). 

This extension enables even more precise and comprehensive sleep diagnostics in practice. The 10-20 EEG system is used for reading and interpreting brain activity. It is used for diagnostic EEGs to identify abnormalities in the brain’s electrical activity, which can indicate a range of conditions including epilepsy and sleep disorders. 

The 10-20 EEG system is based on the placement of the electrodes in relation to certain anatomical landmarks of the head. The positioning of the electrodes is based on specific percentage distances between the electrodes. The numbers “10” and “20” in the name represent these percentages. 

We asked in practice when the use of a 10-20 EEG measurement is necessary and what the characteristics and special features are. We would like to thank Prof. Barbara Schäuble for sharing her practical experience with the 10-20 EEG system with us.

Prof. Dr. med. Barbara Schäuble studied medicine in Freiburg (D) and Glasgow (UK). After training in Zurich, her specialist training was completed in Boston (US) in 2001 and later with FMH certification in Switzerland in 2022. Additional training in epileptology took place at the Mayo Clinic in Rochester, Minnesota (US). This was followed by focused work in presurgical epileptology and pharmacotherapy at the neurology departments of the Universities of Michigan (US) and Bern (Switzerland). Close collaboration with the Epileptology Center in Erlangen then led in 2015 to an adjunct professorship in Neurology (Epileptology). From 2020, the primary focus of sleep medicine training and work was at the Interdisciplinary Sleep Center of the Bürgerspital in Solothurn, under the direction of Prof. Dr. M. Hatzinger. Professor Schäuble is currently a senior physician specializing in rehabilitation and sleep medicine at ZURZACH Care. 

ZURZACH Care operates numerous rehabilitation clinics and outpatient centers specializing in neurological, musculoskeletal, internal oncological and psychiatric/psychosomatic rehabilitation. ZURZACH Care also includes a company for prevention and reintegration as well as subsidiaries and partner companies in the field of sleep medicine at various locations in German-speaking Switzerland.

Which medical issues (clinical pictures) require the use of a 10-20 EEG system and why is the supposedly high number of up to 21 EEG readings needed?

Reports of paroxysmal nocturnal events are common for neurologists, sleep specialists, and general practitioners, but they present a diagnostic challenge. People with epilepsy are more likely to experience sleep disorders and disturbances, such as obstructive sleep apnea (OSA), excessive daytime sleepiness, insomnia, or nocturnal behaviors that do not match typical seizure patterns. In addition, many types of movements or events that occur during sleep can mimic seizures and be misdiagnosed as such. Common examples are NREM parasomnias, sleep-related movement disorders and even REM behavior disorders. 

Conversely, epilepsy syndromes can be mistakenly diagnosed as sleep disorders when the events occur exclusively during sleep or during the transition from sleep to wakefulness – such as paroxysmal nocturnal dystonia. 

Nocturnal seizures and parasomnias have some similar features: Both occur at night, can be accompanied by amnesia for the event, can interfere with sleep and can be triggered by stress or sleep fragmenting factors. Occasionally, sleep disorders and seizures can also occur together.

The importance of treating sleep disorders, especially OSA, in seizure patients has been demonstrated several times.

The medical history with external report is often not sufficient to decide whether a patient suffers from a primary sleep disorder, epilepsy (especially in the frontal lobe) or possibly both. Even video-based observation of movements can make classification difficult. 

The routine EEG is traditionally the most important diagnostic test for patients with suspected epilepsy. With the limitation that a typical event is usually not captured during the short recording period. 

Epileptiform discharges occur exclusively or more frequently during drowsiness or sleep, which often goes undetected in routine EEGs that typically record for only 20-30 minutes. Longer ambulatory EEG examinations do not provide sufficient information on whether a potential sleep disorder is present, as the channels for respiration and electromyography (EMG) are missing. 

In standard polysomnography (PSG), which is used to diagnose sleep disorders and/or to assess sleep architecture, only 4-6 EEG channels are generally used. Although these are suitable for determining the state of sleep, they are often not sufficient to detect focal ictal activity. Interictal epileptiform abnormalities are not visualized in most cases. This has also been shown in several studies. 

Based on these considerations, we most strongly recommend readings combined over multiple days until sufficient data on the reported symptom is obtained and can be clearly attributed.

Many people who see polysomnographic patient wiring for the first time are often astonished: “Is it even possible to sleep properly with all those cables?” With a 10-20 PSG, up to 15 more electrodes are now positioned on the head than with a standard PSG. Do you see the large number of sensors and electrodes applied to the patient as a limitation in the validity of the nocturnal measurements?

The effect of the challenge of sleeping fully assembled in a new environment has been the subject of controversial debate for years. Some sleep studies show the so-called "first-night effect", according to which the quality and quantity of sleep are reduced depending on the environment, illness and age. Some sleep labs mitigate this by conducting recordings in settings such as hotels, at the patient’s home in a familiar environment, or by providing thorough orientation at the sleep lab. Overall, most patients are happy with the additional electrodes; they are less disruptive than an abdominal or thoracic belt.

How many nights is a person measured with 10-20 PSG?

In short, measurements are taken until the event that is to be examined takes place or the patient wants to stop. Here it is important to obtain information on the frequency with which the event occurs in order to reflect the expectations of the referring physician and the person concerned. With very frequent events, experience has shown that a single overnight reading can often achieve the goal. Several days or nights are recommended as a general rule. Provocative maneuvers, such as sleep deprivation, can have a supportive effect.

What is important to you in terms of displaying and analyzing the EEG signals when evaluating a 10-20 PSG?

A large monitor should be used for optimum visualization. Ideally, you should work with two monitors next to each other in order to display the data clearly. A step-by-step evaluation of the extensive data from the overnight measurement is recommended to achieve precise results. 

PSG (polysomnography) and EEG (electroencephalography) can be analyzed separately in detail. Individual assemblies, known as readings, can be pre-programmed for each user, which significantly increases user-friendliness. Various reference points are taken from the electrodes to enable an individual EEG reading. 

The preliminary analyses should also be taken into account. Moreover, good signal quality is crucial for a successful evaluation. Equally important are the professional qualifications and training of the personnel deployed.

Can you share a specific experience where the 10-20 EEG system was crucial?

A connection between obstructive sleep apnea (OSA) and epilepsy had been suspected for some time. I remember one reading in a patient in whom we were able to show that the recorded seizures were also preceded by OSA. The frequency of seizures could then be reduced with CPAP¹therapy. Unfortunately, adherence to the mask therapy was not good and the seizures increased again over time.

What tips would you give to someone working with the 10-20 EEG system for the first time? What challenges are there compared to previous PSGs²?

I recommend not being discouraged by the complex handling of the 10-20 EEG system. As you gain more experience, the process becomes quicker, and certain issues can only be solved through hands-on practice.

I have found that an experienced team is helpful, as well as having two people assist with the wiring whenever possible.

What qualifications should the staff have (for electrode placement and for data interpretation)?

The staff need solid training or guidance in electrophysiological diagnostics and should be highly motivated. Experience is needed to read and interpret the traces (both EEG and PSG). Furthermore, staff must be trained in patient care, including first aid and monitoring during and after seizures.

Prof. Dr. Schäuble, thank you very much for the interview!