This article, in a slightly edited form, first appeared on Pain News Network on September 14, 2019.

In 2017, JAMA Internal Medicine published a manuscript titled “Association Between Persistent Pain and Memory Decline and Dementia in a Longitudinal Cohort of Elders.” While prior research had shown a link between chronic pain and brain damage, this was one of the first publications to specifically suggest that chronic pain can cause dementia.

The authors reported that people with persistent pain experienced a 9.2% more rapid decline in memory score when compared to people of the same age without chronic pain. This means that people with chronic pain may experience more difficulty in managing their finances, medications, and social connections.

Dementia is a chronic condition of the brain that involves memory, personality, and judgment. It is not a disease; it is a symptom of one or more diseases. It usually worsens over time if the underlying disease remains static or progresses, as is the case with many chronic pain conditions.

There are many types of dementia. Alzheimer’s disease is considered to be the most common.

The link between chronic pain and dementia

However, it can be argued that the most common type of dementia is associated with chronic pain. The amount, or severity, of dementia appears to be associated with the severity and duration of chronic pain. Undertreated or untreated chronic pain may accelerate dementia.

According to the JAMA authors, “Persistent pain was associated with accelerated memory decline and increased probability of dementia.” There are an estimated 20 million Americans with high impact (the most severe) chronic pain who may be experiencing accelerated decline in cognition due to their pain.

Seniors, dementia, and chronic pain

Chronic pain affects an even larger percentage of elderly adults (one in three) than the general population. Since the prevalence of chronic pain increases with age, the probability of experiencing dementia increases with age.

However, the reasons for that go beyond aging itself.

Seniors are also more likely to take multiple medications that can contribute to mental confusion. On average, elderly people take five or more prescriptions. They may also use over-the-counter medications, which adds to potential drug-associated mental compromise.

Opioids, in particular, have been implicated in cognitive impairment. However, a study published in 2016 suggests there is no difference in cognitive decline between people on opioids and those on nonsteroidal anti-inflammatory drugs. The study’s implication is that pain, not opioids, leads to cognitive impairment.

How chronic pain affects the brain

Chronic pain appears to affect the function and structure of the hippocampus. This is the region of the brain that involves learning, memory, and emotional processing.

An explanation for the mental decline associated with chronic pain is that various areas of the brain compete for attention. Attentional impairment compromises memory by diverting attention to the areas of the brain processing pain. In effect, the brain is multi-tasking, and it’s favoring the processing of pain over cognition. This may, in part, explain the clinical phrase “brain fog.”

The Australian Broadcasting Company’s “All in the Mind” website explains that pain damages the brain in several ways, including a change in the size of the thalamus and a decrease in the amount of a neurotransmitter (gamma-aminobutyric acid) the brain produces. In other words, chronic pain changes the brain structurally and functionally.

The prefrontal cortex is the part of the brain responsible for executive functions, such as cognition, social behavior, personality, and decision-making. It is also the part of the brain that modulates pain.

According to “All in the Mind,” some researchers believe that chronic pain decreases the volume of the prefrontal cortex. Over time, brains damaged by pain lose the ability to handle pain — along with some of the personality attributes that make us who we are.

Damage caused by chronic pain may be reversible

The good news is that the damage caused by chronic pain can be reversed, at least to some extent. Unfortunately, the elderly are less likely to recover from dementia caused by chronic pain as compared with younger patients. If pain is adequately treated, the brain may be able to regain its ability to function normally.

However, if a brain is to recover from pain associated damage, the pain must be mitigated.

A 2009 report offered evidence that damage to the brain caused by chronic pain can be reversed. At that time, patients with chronic pain due to hip osteoarthritis showed reversal of brain changes consistent with damage when the pain was adequately treated.

People who don’t have their acute pain managed are more likely to develop chronic pain. It is postulated that the changes in the brain that occur with chronic pain begin with the onset of acute pain. There is also some evidence that an individual’s genes may influence who is at greatest risk for developing brain damage from chronic pain, and who is least likely to recover from it.

Many people have criticized the concept of assessing pain as the 5^th vital sign, and have called it a contributing factor for the opioid crisis. As I have said, pain may not be a vital sign, but it is vital that we assess it. Asking patients about their pain is critical to providing interventions that can mitigate the consequences of undertreated pain, including dementia.

Lynn R. Webster, MD, is a vice president of scientific affairs for PRA Health Sciences and consults with the pharmaceutical industry. He is author of the award-winning book, “The Painful Truth,” and co-producer of the documentary, “It Hurts Until You Die.”

You can find him on Twitter: @LynnRWebsterMD.