Absence seizures lead to deficits in consciousness, with relatively little motor or other manifestations. Various tests have been developed to assess awareness, but they are however not performed routinely. [e.g. Repetitive tapping, Simple reaction time (visual or auditory stimulation), Short term memory, Continuous motor performance (tracking), Counting aloud and Verbal response to questions].
Here we describe a device, assembled by the Medical electronics department at the RVI which we have termed ‘Clicker’ device. It comprises of two sounders of different frequencies connected via a jack plug to a DC port of the parallel EEG head box. It is capable of assessing repetitive tapping and testing reaction time to an acoustic signal. The device was used successfully in our routine EEG clinic to establish reduced awareness in association with generalised spike and slow wave (SSW) activity.
A 54-year-old (Mrs S) with a known diagnosis of GGE, treated with two anti-epileptic drugs (AEDs) continued to experience blank spells. The referring neurologist was uncertain whether these were seizures, side-effect of AEDs or behavioural. She reported that the blank spells occurred when she was relaxing and felt a bit of ‘’missed time’’ but wasn’t entirely certain.
There were two parts to the test. The patient was first asked to press the 'clicker' buttons following a metronome flash and then react to an auditory beep (triggered by the technician performing the study).
The button was effectively pressed by the technician in association with spike and wave activity on two separate occasions, with one button press during the first burst and three during the second. Mrs S did not respond to any of these four button presses, but responded to all others during the resting EEG, including just after the end of the spike and wave bursts. These ‘failure to respond’ events were not associated with any visible clinical change.
There were instances where the technician was not quick enough to trigger a beep during the very short SSW burst and hence the patient was not scrutinised at those points.
We have demonstrated a simple test of reaction time testing in a patient with epilepsy to determine true loss of awareness spells, which can have implications for therapy.
The device is easy to manufacture and use. However, it is very operator dependent i.e. how quickly the operator or the technician reacts to spike and wave change to elicit response.