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ADHD and Dementia: What’s the Connection?

Can ADHD lead to dementia later in life?

I recently attended the annual CHADD Convention in Chicago, a large national meeting about ADHD. A speaker I heard there mentioned that there is a link between ADHD and Dementia with Lewy Bodies (DLB), a kind of dementia. I knew of an article several years back that suggested a possible link between the two conditions but had not heard anything else on it since then. As a clinical neuropsychologist, I work with clients impacted by ADHD as well as dementias such as DLB, and so the speaker’s comments intrigued me. I wondered if more research had linked the two disorders since I last read about it.

What Is Dementia With Lewy Body (DLB)?

Before talking about ADHD and DLB, it would help to describe what DLB is. Although many people have not heard of it before, DLB is not a rare form of dementia. It is not anywhere close to Alzheimer’s disease in terms of frequency or public familiarity, but some experts have ranked it as possibly the second most common form of dementia after Alzheimer’s. DLB can look a bit like Parkinson’s disease, and it can sometimes be difficult to tell them apart. A few recent media reports for instance have debated whether Robin Williams showed signs of Parkinson’s disease or DLB before his death.

Microscopic abnormalities inside nerve cells called Lewy bodies (hence the name) occur in both DLB and Parkinson’s disease. The movement problems that occur in Parkinson’s disease also tend to appear in DLB. Like all common dementias, DLB is slow but progressive, leads to multiple cognitive problems, and eventually costs the individual his/her ability to independently handle tasks of daily life. Memory can be impacted in DLB but not nearly to the level that it is diminished in Alzheimer’s disease. Other cognitive problems occur, and the person eventually has difficulty doing tasks that were not too challenging before, like driving a car, managing his/her finances, and making appointments.

Although DLB is difficult to spot, there are sometimes signs that point to DLB in the course of the illness. Some of these involve REM-related sleep problems, fluctuations of on and off weeks in terms of cognition early on, and perhaps most distinctively of all, very detailed and convincing visual hallucinations, often of animals and people, that emerge early in the disease process. The hallucinations are sometimes among the first symptoms of DLB. Frequent falls, dizziness, and incontinence are also sometimes seen in DLB. Hallucinations can also occur in Parkinson’s disease, but these are usually considered a side-effect of medication. Clinicians sometimes distinguish the two conditions by considering tremors and motor problems coming before cognitive symptoms as more suggestive of Parkinson’s disease, and the opposite pattern (cognitive problems before motor symptoms) as more suggestive of DLB. The age of onset for DLB tends to be after age 50.

So Are DLB and ADHD Linked?

So we know what ADHD is, and we know a little bit about DLB. Are they related? Well … possibly.

The study I read before was published in 2011 by Dr. Angel Golimstok and colleagues in Argentina. They thought that ADHD and DLB might be linked because of similar levels of brain chemicals in the two disorders (dopamine and norepinephrine). In the study, people who had probable DLB were more likely to endorse prior ADHD symptoms (the authors stopped short of calling it a prior ADHD diagnosis) than those who had probable Alzheimer’s disease or who had no dementia. I say “probable” here because a definitive diagnosis for either dementia can only be made by autopsy. In individuals who were too impaired to recall the past, their earlier life symptom recollections were obtained from someone close to them who knew their histories. The differences in endorsed past ADHD symptoms were big—almost 48% in the DLB group versus about 15% in the other two groups—but the study was not perfect.

The study had some weaknesses. For instance, reports of past behaviors are susceptible to error; definitive diagnoses of ADHD, DLB, or Alzheimer’s disease were not made in this type of design and it was unclear how characteristic this sample was to the general population. There is also a difference between saying someone has ADHD and someone has some of the symptoms of ADHD or even symptoms that look like ADHD. Still, it did raise some interesting questions about a link between the two disorders.

In science though, to establish a relationship, multiple studies saying the same thing are needed, rather than just the results of one study. It is a point often lost by the media, but no single study is perfect, so rarely can it be trusted by itself as the last word on a topic. Consider how some of the weaknesses mentioned above might lead to inaccurate results.

The interesting thing about the ADHD-DLB link was that the 2011 study got a lot of publicity, but additional studies confirming these results (or even looking at the same topic) were just not found when I searched for them for some time on Google and research publication databases. Perhaps there are other studies out there that confirm the suspicions of these researchers, but if so, they are pretty hard to find, and there are not many of them.

What this suggests to me is that there might be a link between ADHD and later-life DLB, but it is just too soon to make the leap that there is a link between them. This single study just can’t establish that link so conclusively. What it does do is set up a good working hypothesis for other studies to see if a trend of research suggests an ADHD-DLB link. Right now though, it is too soon to consider it a closed case.

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