Epigraph Vol. 24 Issue 3, Summer 2022

Research Recap: Social deprivation and epilepsy incidence

Reported, edited and produced by Nancy Volkers, ILAE communications officer

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Podcast Transcript

Epilepsy is more common in low- and middle-income countries. The reasons are complex, and could include higher rates of head injury, birth complications, and other possible causes. But wealth is never distributed evenly; in any country, some people live with relatively higher levels of what experts call “social deprivation,” which takes into account income, education, housing, unemployment, and other measures.

We spoke with two authors of a study that attempted to tally all the cases of newly diagnosed epilepsy and first seizures during a single year in County Cork, Ireland. They wanted to know: In this relatively homogenous county, were there higher rates of epilepsy in more socially deprived neighborhoods?

Dr. Maloney: My name’s Eimer Maloney. I trained in neurology in Ireland and subspecialized in epilepsy. This research article is part of my Ph.D. research. I‘m now living in Cambridge (United Kingdom) and doing some further training in neurophysiology.

Dr. O’Reilly: My name is Eilis O’Reilly and I’m senior lecturer in epidemiology at University College Cork.

Could one of you provide a little background and context for the study, before we get into the methods and the findings?

Dr. Maloney: In epilepsy research, we still need to understand who develops seizures and why, from the cellular mechanisms to the social constructs. The data in this article were part of a bigger study we undertook to investigate the incidence of seizures and epilepsy in our region. That was the first study of its kind in Ireland. We worked hard to capture all seizure presentations and to carefully characterize and classify them. And I guess then we were able to look at okay, in our particular area, is there a difference in the incidence of seizures and epilepsy between areas of relatively high compared to relatively low socioeconomic deprivation.

There have been some similar large-scale studies in the UK, and there’s been some smaller studies, and some of the results are conflicting, especially in children. I guess unlike some of the previous studies that use database or coding data, we had good detail on the seizure and epilepsy type, we also had acute symptomatic seizures, which hadn’t been researched before, and so we thought we might be able to further clarify and define what’s known. That’s the reason we decide to look at this in particular.

Your data were collected over an entire year throughout County Cork, which covers about 75,000 square kilometers and includes more than half a million people. Can you talk about your collection methods?

Dr. Maloney: We spent a good bit of time planning the study and trying to think about case ascertainment and maximizing case ascertainment and thinking about areas in the hospital or the community where seizures might present, but not necessarily traditionally come to be known in some of the other epidemiology studies. We designed multiple overlapping prospective and retrospective methods and tried to cover acute hospitals and community settings. In brief it involved a review of emergency department triage, radiology, EEG databases, and then regularly liaising with medical and nursing teams in the hospitals, as well as nursing home management and management of residential care settings.

So as much as possible we tried to capture all the cases. And then we reviewed the charts and the investigations of all the cases and had criteria as to say whether this was a definite seizure, probable, or possible. We then did further analysis on just the definite and probable cases.

One thing I was intrigued by was the relative deprivation index. Can you explain a little bit about what that is and why you used it?

Dr. O’Reilly: This is an index developed to pick up indicators from our census that we do every 5 or 10 years, so it brings in variables for local areas and assigns a deprivation index to a geographical area. And the parameters that they use might be the level of educational attainment, the population density, other indicators. It correlates well with other indicators that are out there, but it’s one that’s designed to be applied to the data collected in the census surveys.

So what we did with that information was, we knew where everybody lived, all the patients that Eimer described previously. Because we knew where they lived, we knew what the relative deprivation was in the area within which they lived. So we could then also use the census to know how many people lived in that particular geographical division and could calculate the incidence in each division and assign the deprivation index to that area. That’s kind of how we applied it. We haven’t collected control data, but we’re using the general population from which the cases arose to sort of give us a control level of data.

What were the main findings of the study?

Dr. Maloney: From the whole population, and again we just took the definite and probable cases, in total there were 372 first unprovoked seizures, 336 new diagnoses of epilepsy, and 189 first provoked seizures in the calendar year of 2017. We went on to compare, to divide these up into quintiles based on their address, and so looking at each diagnostic category so for unprovoked seizures and new diagnosis of epilepsy, the incidence in the most deprived quintile was about 1.8 times higher than the incidence in the least deprived quintile, and for first provoked seizure, the incidence was about 1.5 times higher in the most compared to the least deprived quintile.

We subdivided based on age. Because of the census data, we looked at those less than 15 years of age and those 15 years of age and older. For all diagnostic categories, this difference between the most and least deprived quintile was similar. We couldn’t look at provoked seizures in children because there were only 10 cases in the whole population.

We subdivided again looking at new diagnoses of epilepsy by etiology. In structural and etiologies of epilepsy there was about 1.7 times the incidence in the most deprived quintile compared to the least, and for genetic and unknown etiologies it was about twice as high, the incidence in the most deprived compared with the least. But in the genetic group there were quite small numbers so it wasn’t statistically significant.

Was either of you surprised by these findings, or were there any of the sub-analyses that you were particularly struck by, that you didn’t expect?

Dr. Maloney: I think the number, it is similar to what is seen in other populations, but having gone through each case individually in such detail and kind of being familiar with them and then when you take a step back and divide them, and think it’s nearly twice the incidence in the most deprived, I was struck by that. And it seemed like no matter which way we subdivided it, that trend was there.

We also looked at a trend analysis and found a 1% increase in relative deprivation was associated with about a 4% increased risk of unprovoked seizures. That trend suggests the etiology might be multifactorial, and I think that’s also reflected in the way that we could see the association no matter which way we subdivided the cases.

Dr. O’Reilly: I would agree with that and in some ways I think in Ireland, the range from most to least deprived mightn’t be as wide as in other populations. So to still be able to see that kind of trend I thought was quite remarkable. I have an interest in social epidemiology, so to see that socioeconomic status can be a factor, to newly highlight other conditions that are affected by people’s social condition I think is important. It’s important in terms of where we put our resources as well, in trying to prevent disease.

What are the strengths and maybe some of the limitations of the paper?

Dr. Maloney: I think the almost complete case ascertainment is certainly one of the strengths, and hopefully makes it a reliable and robust cohort. It gives us a lot of information about the service needs locally. The other strength of the study is that we used the most up to date ILAE definition of epilepsy and the classifications, so it gives some information about the use of these definitions in practice.

In terms of limitations, it would have been great to have some more descriptive data, more detail, on individuals’ risk factors. When you use population-based tools or region-based tools for deprivation, you can’t account for an individual living in that area who might be an outlier. It would have been great to have individual markers, and then individual risk factors, but because we gathered the data retrospectively, we didn’t have complete risk factor information for each case. I think it will be hard to get that kind of detail at a population level.

Dr. O’Reilly: Ideally, we would have a lot more information about the individuals so we could look at other potential risk factors. But because we were doing this retrospectively, going back to the chart to review, we had no input on what was collected. For example, we might want to know about occupation or other aspects of their life, but we weren’t able to get that kind of detail.

Are there plans for follow up study to this, or a study that was inspired by the results, or anything?

Dr. O’Reilly: It would be good to replicate this in a bigger cohort, not using these specific data but to find another larger study we could use to replicate the findings. We think they’re robust, but it’s always good to replicate everything if we’re interested in this idea of causation. It would be great if we could go back to these patients and do some follow up with them. In terms of more epidemiology studies, I think we might look at some air quality or environmental factors, area-level factors we can attach to an individual based on their address. That might be another avenue we go down whilst doing the IRB work to get permission to go back and re-contact the patients.

Access to care can be a barrier, especially for people who experience higher levels of social deprivation. Were you concerned that may have affected your data?

Dr. O’Reilly: We have a model of care where most people have access without insurance. There is a subset of the population who would have insurance but even within our system where everyone has access to care, there will be underrepresentation in any kind of sought care among people who have more social deprivation. That would mean that the contrast we see is weaker than it might be if we had full access to people in the highest levels of social deprivation. So if anything, then, if this does exist, and I don’t think it exists as much as it might in other jurisdictions, but if it does exist it just means we’ve underestimated the association and we’re at the lower limit of what might be the association.

So if you had to describe this study to someone who wasn’t an expert in the field, the findings of the study, how would you do that? What would you say?

Dr. O’Reilly: I would probably say that we already know that life expectancy is shorter for people who live in the most socially deprived areas, but would you believe that it extends to neurological conditions like epilepsy? And I think it is a little startling that the reach of social deprivation is so wide that across all these categories, provoked, unprovoked, different ages, that it’s persisted.

So it’s also interesting to show that Ireland is not a low-resource country, but like you said, relatively speaking there are gradients of risk.

Dr. Maloney: Yeah I think you were asking what struck me, we think globally, 80% of people with epilepsy coming from low income countries, and we’re in a country that doesn’t have a very, you could say it doesn’t have a very dramatic skew, and we’re also in a particular region of that country.

When you’re looking at the map, as we’re mapping people by address into these electoral divisions, they can be quite close to each other, medium close to high deprivation. To think that there’s something happening at that level that’s causing these findings, it’s quite stark and you kind of, as Eilis said, deprivation can be so all encompassing to affect this particular disease.

Dr. O’Reilly: Speaking of these geographical divisions that the census has created – some of these people were living maybe three or four streets away from each other. And yet we could still capture this, something was still being captured. It’s intriguing and it’s also an injustice, and it’s something you’d love to get to the bottom of.

Thank you both for joining me and talking about your work.

The study is titled “Association between social deprivation and incidence of first seizures and epilepsy: A prospective population-based cohort.” It was published in May 2022 in Epilepsia.