The Burden of Chronic Pain: Many New Cases, Lots of Persistence

In the first study of its kind, researchers examine chronic pain incidence and persistence in a nationally representative sample of adults in the United States. It’s likely the burden of pain is much higher than reported in the study when taking migraine into account.

According to a recent update from the Centers for Disease Control and Prevention (CDC), roughly 21% of American adults experienced chronic pain in 2021. That statistic represents the prevalence of this debilitating and costly condition – a cross-sectional snapshot of how many people in the country had chronic pain at a particular moment in time. Yet, what has been harder to capture is the incidence of chronic pain: How many people across the country newly develop this disorder? How long chronic pain persists has also remained unclear.

Now, researchers led by Richard Nahin, National Institutes of Health, Bethesda, US, use data from the 2019-2020 National Health Interview Survey (NHIS) to determine the incidence of chronic pain, the incidence of high-impact chronic pain (pain that substantially affects life or work activities), as well as the persistence of chronic pain, in more than 10,000 study participants.

The researchers found high chronic pain incidence rates in 2020 in people who had no chronic pain in 2019. Meanwhile, they also saw high rates of persistent chronic pain in 2020 in those who experienced chronic pain in 2019. The authors stress that these findings represent a burden that outpaces that of other chronic diseases like diabetes or hypertension.

Roger Fillingim, director of the Pain Research and Intervention Center of Excellence at the University of Florida College of Dentistry, Gainesville, US, said the results drive home how “robust” a public health problem chronic pain really is.

“These data show us that chronic pain affects a large proportion of the population, and that a not trivial proportion of healthy people are going to develop a chronic pain condition over the next year,” he said. “Many people who work in this field might have assumed chronic pain had a high incidence rate. But these data clearly tell us that chronic pain continues to occur and persist, and it’s a major public health condition that affects new people all the time,” according to Fillingim, who was not involved in the study.

The research appeared May 16, 2023, in JAMA Network Open.

An unexpected longitudinal dataset
Each year, the CDC conducts the NHIS, which collects data from the non-institutionalized US civilian population to understand the amount, distribution and effects of a wide range of health conditions. In 2016, with the rollout of the National Pain Strategy, which pointed to a dearth of pain epidemiology studies, the survey started to include questions about chronic pain.

Generally, Nahin said, the survey would recruit participants for only one year. But during the COVID-19 pandemic in 2020, the survey administrators had difficulty recruiting enough people to participate.

“To recruit enough people, the CDC ended up re-contacting all the participants from the 2019 survey. They asked how many would be willing to take the survey again,” he said. “About 40% of those people said they’d do it again. And while it wasn’t the intent of the CDC, by doing so, they created this longitudinal dataset. When we saw that, we decided to take advantage of it to look at chronic pain incidence.”

The repeat participants would form a dataset of 10,415 adults aged 18 and older. Nahin and colleagues determined chronic pain status by asking them: “In the past three months, how often did you have pain?” If the participant answered “most days” or “every day,” they were classified as having chronic pain. The researchers also analyzed data on high-impact chronic pain, asking if pain limited the participant’s life or work activities during the past three months. If participants reported that they felt limited most days or every day, they were designated as living with high-impact chronic pain.

The researchers would look at incidence rates of chronic pain in chronic pain, non-chronic pain, and no-pain groups. They defined incidence as the development of chronic pain in 2020 after having been pain free in 2019, and an incidence rate would be calculated, namely, the number of new cases of chronic pain per 1,000 person-years (PY).

The investigators would also assess the persistence of chronic pain in 2020 in those who reported pain in 2019, per 1,000 PY. Finally, they looked at demographic characteristics like age, sex, race, and education level to examine whether any of those features were associated with lower or higher incidence rates.

The results boost the case for prevention
The researchers based their incidence estimates on the 3,776 people who were pain free in 2019 but had pain in 2020. The chronic pain incidence rate in 2020 was 52.4 cases per 1,000 PY, and the high-impact chronic pain incidence rate was 12.0 cases per 1,000 PY, in adults who had no pain the previous year. They also found that among those who had pain in 2019, the rates of persistent pain in 2020 were 462 cases per 1,000 PY for chronic pain, and 361 cases per 1,000 PY for high-impact chronic pain.

The risk of chronic pain was highest in older people and those without a college degree, while there was little difference between male and female participants (the study included roughly an equal number of both).

Looking at the numbers another way, in terms of one-year cumulative incidence, 61.4% of those with chronic pain in 2019 still experienced it in 2020. Meanwhile, 14.9% of people with non-chronic pain in 2019 said they had chronic pain the following year, 6.3% of people without pain in 2019 developed chronic pain in 2020, and 1.4% had incident high-impact chronic pain.

To put the findings in perspective, the incidence of chronic pain in the current study was more than seven times higher than the incidence of diabetes (52.4 vs. 7.1 cases per 1,000 PY), three times higher than the incidence of depression (which had 15.9 cases per 1,000 PY), and it also was higher than the incidence of hypertension (45.3 cases per 1,000 PY).

Going into the study, Nahin said, “We really had no idea what the numbers were going to look like. One of the most surprising things to us was how stable people’s pain status was. Most of the people who had no pain in 2019 also had no pain in 2020. Most of the people who had chronic pain in 2019 still had chronic pain in 2020. Your pain status seemed to be based, to a large extent, on your status the year before. We did not expect that. Only about 10% of people with chronic pain fully recovered.”

That’s why early intervention is so important, Nahin said.

“Clearly, once you develop chronic pain, it’s difficult to get rid of it. You want to prevent it from developing, if at all possible,” he said. “Now that the Centers for Medicare & Medicaid Services [CMS] have changed their billing and are more willing to support multidisciplinary, multi-intervention procedures for chronic pain, there is more that clinicians can do. These data show that we really need to expand this type of multidisciplinary care so we can help more people and prevent chronic pain from happening, whenever possible.”

Drilling deeper into the data
Nahin said he fully expects others to use the NHIS dataset for additional studies.

“There’s so much you could do with these data,” he said. “I think a lot of people will be publishing studies on it within the next year or two.”

Fillingim said he hopes the results will help those with the power to affect public policy and research funding to understand just what a “tremendous” public health burden chronic pain is – and act accordingly. Yet he cautions that the findings, as compelling as they are, may actually “undersell” the impact of chronic pain, pointing to migraine as an example. (The researchers could not parse the data according to headache, migraine, or other specific pain conditions, since NHIS does not collect such information.)

“I would suspect that many people living with migraine conditions would not meet this study’s definition of chronic pain. They may not have pain most days or every day, but we know that migraine is a pain condition with a lot of negative impact. There are many people who may be suffering who aren’t included in this analysis,” he said.

“And if we can get this kind of high-fidelity data on prevalence and incidence for different conditions like migraine,” Fillingim continued, “we may be able to identify protective or exacerbating factors that determine whether someone who has a chronic pain condition gets better, worse, or stays the same. In the future, that kind of information has the power to guide the development of more effective treatments.”

Kayt Sukel is a freelance writer based outside of Houston, Texas.

Reference
Estimated rates of incident and persistent chronic pain among US adults, 2019-2020.
Nahin et al.
JAMA Netw Open. 2023 May 1;6(5):e2313563.