NEUROIMAGING FOR EPILEPSY

The clinical and cost-effectiveness of technologies used to visualise the seizure focus in people with refractory epilepsy being considered for surgery: a systematic review and decision analytical model

Background

Epilepsy is the most common serious neurological condition; approximately 456,000 people in the UK have a diagnosis of epilepsy. Epilepsy is usually controlled using antiepileptic drugs though approximately 20-30% of people continue to have fits despite drug treatment. For people who do not respond to drug treatment, surgical removal of the part of the brain where the epileptic seizures originate may be considered, as this can result in the person becoming seizure-free.

Before surgery can take place, the epileptic focus must be identified. To do this a range of diagnostic tests can be used. In the UK NHS, usual practice is to obtain details of the person's medical history, undertake a clinical examination, and perform an electroencephalogram (EEG) and a routine magnetic resonance imaging (MRI) scan. Individuals will usually go on to have continuous video and EEG recording in order to record seizures and identify the likely seizure focus. If these are unsuccessful three broad alternatives will need to be considered. Firstly, if there is a clear indication as to the site of the seizure focus the person may be admitted to hospital for continuous invasive EEG monitoring with electrodes inserted into, or across the surface of, the brain. Secondly, if there is no clear indication as to the site of the seizure focus, and it is considered unlikely that the patient will benefit from surgery, a decision might be made not to continue with the pre-surgical evaluation. Thirdly, and the most common, would be a decision to proceed with further, non-invasive, investigations such as specialised imaging scans or magnetoencephalography (MEG).

The main aim of this project was to provide further information about the likely site of the seizure focus so that a decision can be made as to whether to proceed with invasive EEG monitoring, proceed to surgery, or to halt the pre-surgical evaluation.

Findings

Clinical research into imaging for the localisation of epileptic foci is abundant but not adequately informative because: there is no acceptable reference standard for the assessment of the diagnostic accuracy of tests to identify a seizure focus in patients with refractory epilepsy; diagnostic accuracy studies reporting clinical outcomes tend to do so only following surgery; the outcome prediction studies identified are based only on patients who have undergone surgery, and have small sample sizes; decision level and effectiveness studies are lacking.

The additional value of any diagnostic strategy for the localisation of epileptic foci is closely related to the impact on treatment decisions as well as the value of the treatments themselves (MM or surgery); this needs to be considered fully in informing cost-effectiveness assessments in this context. Therefore, future appropriately designed studies need to determine the added value of diagnostic regimens in terms of informing decisions on the appropriateness of surgery and in terms of clinical effectiveness and cost-effectiveness.

The feasibility of developing a national registry should be considered to collect standardised information regarding the diagnostic pathway, decisions made along the pathway, and clinical outcomes, for all patients who receive work-up to determine whether or not they are eligible for epilepsy surgery. Existing and future research needs to be considered closely in relation to how the research informs the different levels of the diagnostic evaluation framework and ultimately how this links to the actual decision problem(s) faced by clinicians and the NHS; the role of decision modelling is central to this more general issue.

Conducted by: CRD

Further details

Project page on NIHR HTA Programme website

Publications

Burch J, Hinde S, Palmer S, Beyer F, Minton J, Marson A, Wieshmann U, Woolacott N, Soares M. The clinical effectiveness and cost-effectiveness of technologies used to visualise the seizure focus in people with refractory epilepsy being considered for surgery: a systematic review and decision-analytical model. Health Technol Assess 2012;16(34):1-164

Burch J, Marson A, Beyer F, Soares M, Hinde S, Wieshmann U, Woolacott N. Dilemmas in the interpretation of diagnostic accuracy studies on presurgical workup for epilepsy surgery. Epilepsia 2012; 53(8):1294-302

Funding

Commissioned by the NIHR HTA Programme as part of the Technology Assessment Report (TAR) process