Assessment 2 – Objective seizure detection with biosensors
My first assessment for epilepsy evaluation concluded that persons with epilepsy (PWE) unfortunately have little to no ability to reproducibly predict the onset of their own seizures. Therefore, subjective impressions are of marginal value. Given that, there is a vital need for devices or instruments with ability to objectively predict a seizure.
Many devices called biosensors are already available (see reviews Nagaraj et al., 2015; Ulate-Campos et al., 2016). The capability of existing biosensors to predict seizures varies with the specific device. Unfortunately detection and prevention are generally not part of the same device. Despite the fact that current biosensors (with possibly one exception) are only able to detect seizures, nevertheless, they represent a significant first step to development of something more sophisticated with therapeutic value. Furthermore, present day biosensors supply information on seizure frequency, important information that PWE are unable to provide due to an inability to recall the seizure (Hoppe et al., 2015). As a note of caution, biosensors to date are useful only in certain types of seizures and so to be of benefit, appropriate biosensor selection requires accurate seizure type identification (Ulate-Campos et al., 2016).
How biosensors work
There are numerous biosensors in use that detect seizures but generally they do not as yet predict seizures within a reasonable time frame for adequate intervention. Some biosensors record muscle movements e.g. surface electromyography (Conradsen et al., 2012), measure change in muscle acceleration called accelerometry (Beniczky et al., 2013), or measure movement via mattress sensors (Poppel et al., 2013). Other biosensors record effects produced by activation of the autonomic nervous system. This includes measurement of sweating (electrodermal activity, EDA), heart rate (electrocardiogram, EKG), respiration, body temperature and combinations of these with sophisticated computer programs (Ulate-Campos et al., 2016).
The aforementioned biosensors target seizures in which muscle and autonomic nervous system changes are evident and occur before a seizure. Other biosensors use near-infrared to detect changes in brain blood flow prior to a seizure (Tewolde et al., 2015). Ulate-Campos et al., 2016 lists the more than 40 available biosensors and their web sites.
EEG and intracranial electrodes – important contributions
However, for all seizures, the gold-standard for seizure detection is the electroencephalogram (EEG). The EEG records the summation of brain wave activity via topically attached electrodes positioned around the scalp. Unfortunately, everyday use of the EEG is incompatible with daily life.
Another approach, intracranial electrode implantation (iEEG), provides continuous long term measurement of brain activity in the seizure prone region. Results of small studies and clinical trials with the iEEG (Iasemidis et al., 2003; Cook et al., 2013; Spencer et al., 2016; Karoly et al.,2018; Baud et al., 2018) have confirmed the presence of
a) unique neurological activity termed epileptiform discharges that occur with a regularity of 24 hours (circadian) or over several days (multi-day), and
b) the relation of aspects of these rhythms (phases) with seizures in PWE with low to moderate seizure frequency rate (Baud et al., 2018).
NeuroVista Advisory System is an example of the iEEG that has undergone clinical evaluation. NeuroVista Advisory System employs an assessment system using sophisticated algorithms. In clinical trials (Cook et al., 2013; Bergey et al., 2015) it performed with reasonable success. In several cases where seizure prediction fell below pre-designated criteria, optimization of the computer system i.e. its algorithms, dramatically improved predictability of the seizure. Thus it appears possible to tailor the algorithm to each patient to achieve the best result (Kuhlmann et al., 2018).
Although the iEEG successfully analyzes prodrome data (see Assessment 1) to predict a seizure and hence supplies information in a sufficient time frame to avert a seizure, it is not without serious concerns. An implantation of intracranial electrodes is an invasive technique requiring major surgery and carries the risk of infection and related brain problems.
Biofeedback Biosensors – hope for the future
The most desirable biosensor is one that employs a biofeedback loop with both
1) reliable seizure detection and
2) appropriate and effective therapeutic intervention that prevents the seizure.
Neuropace Responsive Neurostimulation (RNS) (http://www.neuropace.com) device is an example of a biosensor with a biofeedback loop. The device is implanted in the brain and detects epileptiform discharges and delivers neurostimulation to suppress the seizure. Results of a two year clinical trial with 191 medication- resistant PWE, showed significant decline in seizure frequency (Heck et al., 2014). The PWE enrolled in this trial had intractable partial-onset epilepsy. The development of the Neuropace RNS is a significant achievement for select PWE. However, the biggest limitation is the requirement of major surgery for implantation of this device.
Characteristics of the ideal biosensor
The ideal biosensor would monitor seizure-related external biological phenomena such as EKG, EDA, muscle movement blood flow etc., as discussed above and accurately assess the data to predict a seizure. Additionally, seizure detection would be linked with effective seizure prevention measures. This could take the form of a) an alert to a caretaker to give appropriate therapy, b) neurostimulation or c) minipump infusion of appropriate mediation (Ulate-Campos et al., 2016). Additional characteristics of the ideal biosensor include safety and efficacy without false alarms, user friendly instrumentation, ease of care, wireless transmission of data and full compatibility with daily life (Hoppe et al., 2015).
Questions for readers
Comments on this blog are welcome. Experience with biosensors would be appreciated.