Clinical neurophysiology clinical outcomes

Clinical outcomes are broadly agreed, measurable changes in health or quality of life that result from our care.  Constant review of our clinical outcomes establishes standards against which to continuously improve all aspects of our practice.

About the Clinical Neurophysiology Service

Picture of Oliver getting ready for electrode placement
Oliver getting ready for electrode placement

Video electroencephalography (EEG) telemetry is an investigation during which brain waves are recorded for a prolonged period, usually for one to five days. The EEG monitors brain activity using electrodes that are placed on the scalp or with special electrodes placed directly on the brain surface, known as invasive recording (IM). Video EEG telemetry is widely performed in the UK to help evaluate paroxysmal events (seizures or fits), diagnose epilepsy, and to plan surgery in patients with epilepsy who have not responded to other forms of treatment. At Great Ormond Street Hospital (GOSH), we admit around 200 to 250 children per year for Video EEG telemetry. The Telemetry Suite consists of a four-bed unit based on Koala Ward, allowing long-term recording of brain activity with synchronised video. The majority of patients admitted are investigated for pre-surgical evaluation (PSE) and characterisation of seizures (SC). 

About epilepsy diagnosis

Picture of a patient's drawing of an EEG
Patient's drawing of an EEG

A diagnosis of epilepsy is made when an individual is prone to recurrent epileptic seizures. There are many different causes, and consequently many different types of epilepsy. One in 20 people will experience an epileptic seizure in their lifetime and one in 200 will experience recurrent seizures resulting in a diagnosis of epilepsy. Up to 75,000 children and young people have epilepsy in the UK, which makes it more common than diabetes.

Diagnosis can often be difficult and misdiagnosis occurs in up to 40 per cent of cases. This is because there is no single diagnostic test – diagnosis relies on the expertise of professionals from multiple specialties to determine whether a description of events is compatible with a seizure, and EEG is one of them. So a ‘multi-disciplinary team’ approach is very important in the diagnosis of epilepsy. 

After a diagnosis of epilepsy has been made, EEG and Video EEG telemetry can help determine the type of epilepsy. EEG can also help to determine treatment and, in the case of drug-resistant epilepsy, determine whether epilepsy surgery may be an option.

However, the nature of epilepsy is that seizures are unpredictable and vary in frequency – some children may experience seizures every day while others may experience them only several times a year. The rate of seizures can also change dramatically, even without a change in medication. So, for example, a child may not experience the rate of seizures today that they were experiencing four months ago. 

Children who are admitted to the telemetry unit with infrequent seizures (less than two to three per week, for example) may need to have their drug reduced or stopped in order to increase the likelihood of a seizure while they are admitted – so that brain activity can be recorded during the seizure. Video EEG telemetry is a finite resource and so commonly children are only recorded for between one to five days and may have to be re-admitted if the question has not been answered in this time period.

Reasons for admission

Reasons for admission to the telemetry unit can be grouped into five categories:

  • Seizure characterisation (SC).
  • Pre-surgical evaluation (PSE).
  • Pre-surgical evaluation with single positron electron tomography (PSE/SPECT).
  • Diagnosis of electrical status epilepticus during slow wave sleep (ESES).
  • Invasive monitoring/electro cortico-graphy (IM/ECoG) recordings from the brain surface involving surgery.

Reasons for Clinical Neurophysiology admissions 2007-2012
Reasons for Clinical Neurophysiology admissions 2007-2012

Diagnostic outcome measure

As a diagnostic service, our key outcome measure is whether the results of the investigation can answer the referral question, which in turn will guide a child's treatment. This is influenced by the referral criteria and the question asked, but it is a good measure of our effectiveness as a service. 

Our outcome measure consists of three categories:

  • success
  • partial success
  • failed

The success criteria are different for each investigation type:

For SC and PSE, success is deemed if we captured the events in question; partial success if we captured some types of events but not the range of events a child may be having. For ESES, success is deemed if we recorded sleep. PSE with SPECT is recorded as successful if the child was able to have the injection for the SPECT scan. In some patients, seizures were recorded but occurred outside the 'SPECT window' (time period in which the SPECT tracer can be injected (usually around four to six hours). In this case, the SPECT is a failure, but PSE is a success. Invasive monitoring is a success if it was completed and is considered a failure if there were complications that led to the monitoring being stopped before a decision about surgery was made.

Results

The graph below shows our results by investigation type, since 2007. It shows that our success rate over the last five years is between 70 per cent and 75 per cent for the investigations we do most frequently – seizure characterisation and pre-surgical evaluation. Pre-surgical evaluation with SPECT is the least successful investigation due to the fact that seizures have to occur during a short time period to be successful (four to six hours). Nevertheless we still have a success rate of more than 50 percent for this evaluation, which is excellent in comparison to other international epilepsy centres.

Diagnostic evaluation of ESES is 100 per cent, as we are always able to capture sleep in an overnight recording. Invasive monitoring and ECoG have a very high success rate as these invasive investigations are only performed in complex cases and are very carefully planned. Furthermore, some information such as delineation of the abnormal brain area and documentation of brain function are data that are always gathered during the monitoring period.

Outcome of investigations performed 2007-1012
Outcome of investigations performed 2007-1012

The graph below shows our overall results since 2007. We have higher numbers of patients, and higher success rates overall, with 173 investigations resulting in an answer to the referral question in 2012 compared with 130 in 2007. However, while our success rate is higher, there is also a slightly higher rate of partial success and failure to answer the referral question. Analysis suggests that this is related to the higher rate of complicated cases we now see, and some service changes.

Overall outcome of investigations performed 2007-2012
Overall outcome of investigations performed 2007-2012

Outcomes data is a valuable source of information in our quest for continuous improvement of our services. As a result of these data, we have made the following improvements to our service:

  • Increased scoring consistency by moving from a guided individual scoring model to a multi-disciplinary team scoring model.
  • Clearer evidence-based admission criteria, to target the patients who can benefit most from our SPECT service.
  • Phone calls to parents to confirm seizure frequency three to 10 days before admission.

Dr Ronit Pressler, MD PhD MRCPCH, Consultant Clinical Neurophysiologist, Clinical lead Telemetry Unit.

Kelly St. Pier (CSci), Neurophysiology Professional Service Manager (Video-telemetry).