JAMA Internal Medicine Study Links Chronic Pain and Dementia

Chronic pain is an epidemic in the US, but
this study, appearing in JAMA Internal Medicine suggests that the consequences of chronic
pain may extend beyond quality of life issues. Researchers led by Elizabeth Whitlock at UCSF
examined data from the Health and Retirement Study, a longitudinal survey study of just
over 10,000 older adults. Every two years, the participants provided
answers to questions about pain and cognition, along with a host of other factors. They divided that group into the 1,120 individuals
who reported moderate to severe pain in both the 1998 and 2000 surveys, and everyone else. As you can see here, these folks were quite
different at baseline. People with persistent pain were less likely
to be male, were less educated, less financially secure, and had a greater burden of comorbidities,
especially depression. But the question was whether the people with
pain would have a more rapid decline in cognitive function, or a higher risk of dementia. I think the risk of dementia analysis is the
most salient here. Start with the graph on the left. The x-axis shows us time in years from the
year 2000 visit. The Y-axis shows us the predicted dementia
probability. Now, why not just show us the rate of dementia? Well, the researchers didn’t have access
to that data – this was just a survey. So they used a technique to convert the survey
answers to a predicted dementia risk. In other words, for each person they could
hang up the phone, enter the data into a model, and say – huh – that guy has a 50% chance
of being demented. No, it’s not perfect, but it’s not bad. In any case, the left box shows us the unadjusted
risk. People with persistent pain are clearly at
higher risk of dementia over time. But when you account for all those baseline
differences, as they do in the graph on the right, those risks get majorly attenuated. And this gets us to an interesting issue. We have a few ways to interpret this. One possibility is that pain really does damage
the brain. It’s not so far-fetched. Persistent pain may lead to significant cortisol
elevation which can certainly alter brain chemistry. If you buy that, you’d expect that aggressive
treatment of pain in the elderly, perhaps even with opiates, will reduce the risk of
dementia. But there’s another possibility. Maybe it was the treatment of the persistent
pain in this group that caused the cognitive decline. We have no details with regards to how the
individuals with pain were being treated. If some of them were receiving opiates, is
it crazy to think that opiates were causing their brains to run a bit slower? But here’s my version of Occam’s razor
for medical studies: given multiple interpretations of the data, the least interesting tends to
be correct. In this case, I think pain is most likely
just a proxy for poor overall health status and neither treatment of pain, nor avoidance
of treatment of pain will do much to alter the rate of dementia in this population.

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