Special Report: What if medication doesn’t help?

Epileptic seizures may be rare events and they cannot be predicted. This unpredictability has psychological and social consequences. Patients suffering from frequent seizures feel a loss of control associated with their reduced motor control, with anxiety and depression as the likely results.

If you have been diagnosed as epileptic, you will have to take anti-epileptic medication in an effort to become seizure free. Anticonvulsant medication may accompany you for your whole life. If a single medication is not effective, adding a second or even a third may be the only choice; but what if you are one of the 20-30% whose seizure activity cannot be controlled by drugs?

During an epileptic seizure, abnormal and synchronised firing of neurons results in paroxysmal depolarisation. Primary, generalised seizures start in both hemispheres of the brain without focal localisation and typically have tonic, tonic-clonic, myoclonic manifestations. Forms of partial seizures begin in one hemisphere and in focal areas of the brain with no effect on consciousness. If you suffer from partial seizures there is hope that a neurosurgical intervention may help you to become seizure free.

The goal of epilepsy surgery is to identify the region in the brain where seizure activity originates and remove it without causing any significant functional impairment. Before surgery can be accomplished, a detailed pre-surgical evaluation is required. Most prominent is the question of whether the seizures are focal or generalised. If focal are they of temporal origin? Is there a lesion associated with the seizures? Imaging technologies, especially MRI, are very useful to detect abnormalities of the brain. SPECT is also very helpful because the isotope injected at seizure onset is concentrated in the region of onset available for imaging studies several hours after the injection.

The most prominent intervention in pre-surgical evaluation is electroencephalography (EEG) recording with time-synchronised video monitoring. Video-EEG recordings may last for several days, yielding hours of ictal (during seizures) and interictal (between seizures) data for analysis and detailed evaluation. EEG activity just preceding seizure onset is specifically analysed in detail to learn more about the focal onset and spreading of the paroxysmal depolarisation to specific cortical areas. During this time of video-EEG monitoring, medication will be gradually reduced to provoke seizure activity for detailed analysis. This means that patients will stay at specialised centres under full supervision for their safety.

During the pre-surgical evaluation, neuropsychological testing and psychosocial assessment will be performed prior to surgery. Once a primary epileptogenic region has been identified it may be necessary to probe further using some form of implanted electrodes. The risk of surgical intervention has to be counterbalanced by the hope of acquiring conclusive data from epidural, subdural or intercerebral depth electrodes to localise seizure onset activity in a certain brain area previously identified by EEG recording using surface electrodes. Especially subdural metallic electrodes in forms of rectangular grids and strips are being used in pre-surgical evaluation. These electrodes are placed subdurally on the surface of the brain. Due to their proximity to the electrical generators within the brain and due to no EMG (muscle)-induced artifact activity, the diagnostic quality of such recorded electrocortigrams is high. However, the placement of subdural grid electrodes requires a craniotomy. Strip electrodes can be placed through burr holes over the lateral convexity or under the frontal or temporal lobes.

If pre-surgically obtained information consistently points to a single area of the brain for seizure onset, then a surgical resection of this area may be indicated.

To ensure that resection of brain area will not cause a cognitive of neurologic deficit, centres using subdural recordings can use the electrodes to stimulate the small region between neighbouring electrodes to gather cortical mapping.

With new fMRI technology it is possible to perform echoplanar imaging while the patient engages in a specific task such as fist clenching, verb generation, tongue movement, etc.).

If the surgical resection of the well-identified brain area is successful, the patient may benefit (60-70% of all cases) from a seizure-free life after the intervention.

Dieter Grossegger, PhD
Chief Executive Officer
Dr Grossegger & Drbal GmbH
alpha trace medical systems
+43 (0)1 368 1797
http://www.alphatrace.at