Background
Chronic pain, which can range from mild to severe, is defined as pain that persists or progresses beyond the ordinary duration of time required for the body to heal from an insult or injury [
1]. Reports approximate that the number of adult chronic pain sufferers in the United States is around 100 million [
1,
2]. The National Institutes of Health, along with the Institute of Medicine, have stated that: “Pain is a significant public health problem in the United States” [
1]. For this reason, National Pain Strategy was developed to emphasize the need for the development of a comprehensive population-based strategy to address the public health problem, improve prevention and care for chronic pain patients, address the health disparities associated with the disease, improve public awareness around chronic pain conditions, improve service and delivery of care to patients, and increase professional education and training. Furthermore, optimal solutions for treating chronic pain are urgently needed as chronic pain-associated annual costs are estimated to range from $560 to $635 billion [
2]. These costs are more complex than just the cost of medication and doctor office visits. Costs also include the loss of productivity in work, and disability assistance needed until a person suffering from chronic pain is able to return to work, if able to return to work at all [
3‐
5]. Altogether, these facts point to the need for an increased understanding of the demographics and socioeconomics of patients living with chronic pain.
The public health problem surrounding chronic pain is further complicated by the use of opioids as a treatment for chronic pain. Opioids have been the go-to treatment for chronic pain for the past 30 years, despite the lack of studies to back up the efficacy or safety of these drugs for treatment of chronic pain [
6‐
10]. Recently, 2.1 million Americans were reported to be addicted to prescription opioids, and six out of ten drug overdose deaths involved opioid use [
11]. Nationally in 2014, there were 18,893 opioid-related deaths, which is a 3.4 increase since 2001 [
12]. Now officially classified as an epidemic, the current opioid crisis has been fueled by the overprescribing of opioids, lack of adequate comprehensive treatment of pain, and limited understanding of the etiology of chronic pain. Epidemiological data has shown that use of opioids results in greater likelihood of patients developing an addiction to opioids [
13‐
15]. Pain patients that have previously been prescribed opioids are more susceptible to substance abuse disorders [
16]; one study estimated a 25 times lower rate of abuse and/or addiction in patients without a prior history of opioid use compared to patients with prior use (0.19% vs. 5%, respectively) [
17]. While opioids are still an effective treatment for some acute and chronic pain sufferers, patients treated with opioids often develop tolerance to opioids that leads to the subsequent increases in opioid dosages for pain management. Thus, the use of opioids in treatment of chronic pain remains a gray area in medicine and the efficacy and safety of an opioid prescription needs to be determined on a case-by-case basis. Furthermore, chronic pain has been increasingly recognized as a biopsychosocial condition [
18‐
20] and comprehensive interdisciplinary management of chronic pain is preferred over medication alone [
21].
According to the US Census, Maine was the oldest state in the country in 2010 [
22], and the second oldest in 2015 [
23]. In 2010, 15.9% of Maine residents were over age 65 [
24], and the median age of Maine residents was 42.7 [
24], which was greater than the US median age of 37.2 [
25]. While the age range with the greatest numbers of chronic pain sufferers is early adulthood to middle age [
26‐
28], the numbers of chronic pain sufferers relative to the total population of a given age increases with age [
29,
30]. Therefore, with its significantly larger older population, Maine is more likely to have a greater chronic pain population and face an increase in chronic pain-associated healthcare burden. Also of significance is the fact that Maine is one of the states that has been hit hard by the opioid epidemic. For example, in 2015, there were 272 deaths in Maine from drug misuse; 111 of those deaths were related to use of opioids (or 41%), an increase from 104 in the previous year [
31].
In this study, to address the knowledge gap regarding the characteristics of the chronic pain population in the state of Maine and the goals of the National Pain Strategy, we identified and characterized the population of Maine residents who suffer from chronic pain through a secondary database analysis using the Maine All Payer Claims Database (MEAPCD) (Data collected between 2006 and 2011). The relationship between the prevalence of chronic pain and a series of social and economic factors were also assessed in combination with the Maine 2010 Census data. We expect that our current study will be the beginning of a series of studies that will help to 1) identify the common demographic, socioeconomic, and geographic factors associated with the chronic pain population within the state of Maine, 2) estimate the burden of chronic pain imposed on the Maine economy through public healthcare needs, and 3) bring awareness to this public health issue and further reduce stigma towards chronic pain patients. All of these factors are vital pieces of the puzzle that need to be put together to create a more efficient understanding of chronic pain conditions and better management of chronic pain both at the individual patient level and at the state level.
Discussion
Maine is currently one of 30 states in the US that maintains an APCD (All Payer Claims Database, a collection of insurance claim data), is in the process of implementing an APCD, or has strong interest in implementing an APCD [
32]. APCDs are a relatively new resource for health data that can be utilized for large scale population studies. The current study used MEACPD to identify and examine the chronic pain population in the state, with the hope to recognize areas for improvement and populations that are experiencing the greatest rates of chronic pain [
33,
34]. In turn, we hope that this information will be used to design strategies that address possible health disparities associated with the chronic pain sufferers.
According to others’ reports, at any given point, 30% of the adult population suffers from chronic pain [
1,
35]. We used a previously validated method to identify the chronic pain population from the MEAPCD [
28]. On average, our parameters identified 330,054 people from a total of 1,119,509 individuals, or 29.5% of the total Maine population (range 25–30%) as having chronic pain, which is similar to the reported percentages. Since we did not include people with ICD-9 codes associated with facial or migraine pain, and the database did not include people without insurance or individuals utilizing veterans’ assistance programs, the actual numbers of chronic pain sufferers in the state are likely to be higher.
Maine was one of 30 states that saw a significant increase in opioid-related deaths between 2010 and 2015, increasing from 9/100,000 opioid-related deaths in 2010 to 23/100,000 deaths in 2015 [
36]. Trends in nation-wide opioid-related deaths have been on the rise since 2000 [
12], which corresponds to the quadrupled prescribing rates of opioids as a pain reliever seen between 1999 and 2008 [
37]. Consistent with these findings, we did notice a gradual increase in the population that had an opioid prescription for 90 consecutive days or more (43,846 (15.8%) in 2006; 56,498 (16.5%) in 2007; 59,985 (16.5%) in 2009; and 63,475 (18.8%) in 2010). Many have speculated the opioid use for chronic pain is partially to blame for the current epidemic. Contrary to this, in our study the majority of the chronic pain cohort was identified through the ICD-9 code criteria (> 80%) and not through the opioid prescription criteria. We found only 15.8–18.8% of chronic pain patients received an opioid prescription for more than 90 consecutive days (Fig.
2), which is consistent with the observation made by Tian et al. (2013), which found that 17% of a chronic pain population received at least a 90-day prescription of opioids. However, it was noted by Tian et al. that many chronic pain patients received opioids for less than 90 consecutive days as 43% of the chronic pain population receiving any opioid prescription over the course of a year [
28]. It is important to mention that opioid prescriptions do not indicate if the prescriptions were filled or used as directed. In future studies, it would be very valuable to determine whether the reason for many chronic pain patients not receiving long-term prescription of opioids is that they received other types of pain treatment or that they simply did not have access to adequate pain management.
All age ranges were included for this study because: 1) the median age of the state of Maine is greater than most other states, and 2) chronic pain conditions in populations under the age of 18 have been found to be increasing over the past few decades [
38], emphasizing the importance of monitoring and treating chronic pain in children. Our data showed that the percent of chronic pain patients increased exponentially with age, particularly after age 65 (Fig.
3g and
h). This is supported by other studies that reported increased prevalence of chronic pain in older populations [
35,
39‐
41]. As Maine is one of the oldest states in the nation, Maine faces a potentially greater burden of chronic pain. Studies have found that people over the age of 35 are at increased risk for developing chronic pain conditions [
26,
27,
29,
42]. Our study revealed that the greatest number of chronic pain sufferers were between the ages of 50 and 55 in both males and females (Figs.
3a–
3f). This is also of relevance to the state’s economy as Maine has more 50–55 year-olds in the work force due to the median age of the state being higher than national average. With chronic pain increasing in this age group, there are more individuals who may find working difficult with chronic pain and more likely to require government assistance (Fig.
6). Thus, ensuring adequate management and prevention of chronic pain are particularly crucial for the Maine economy.
One of the most notable findings from our data analysis is that the prevalence of chronic pain was significantly higher in females than in males in all Maine counties, and in all age groups, with the exception of individuals younger than 10 (Figs.
3 and
4). Previous studies have observed greater prevalence of chronic pain in females compared to males [
26,
43]. This may indicate the increased length of chronic pain experienced by women, thus one explanation for why the prevalence of chronic pain remains higher in women compared to men nationwide. The exact reason for why chronic pain is more prevalent in women is not fully understood. It may be related to the fact that women tend to use healthcare more frequently than men [
27], and that sex-linked differences in the neurobiology of pain and pain perception. Furthermore, Maine women earn less than men and are more likely to live in poverty, which can put them at greater risk for developing chronic conditions [
44,
45].
Employment status, occupational factors, education, and income have been inversely associated with chronic pain [
46‐
49]
. Our study did not detect an association between the prevalence of chronic pain vs. levels of education or income (data not shown) based on Maine county reports. In 2010, Maine had an education level higher than the national average [
25,
50], which may explain the lack of correlation between the prevalence of chronic pain and education status. Also
, since all data are analyzed at the county level, our study may not be sensitive enough to detect these correlations because Maine counties are composed of more towns than cities and the diversity between the two may mask any differences that may be seen at the individual level
. However, we did reveal significant negative correlations between income and education levels and the usage of public insurance (Fig.
6), highlighting the close relationship between one’s socioeconomic status and health insurance type. Future detailed analysis at individual levels is necessary to reveal the relationships between the prevalence of chronic pain and socioeconomic status, education status, or usage of the public health system within the state of Maine.
Comparing the insurance used by chronic pain patients allowed us to determine if there is an association between chronic pain prevalence and the insurance type (private vs. public assistance) utilized by chronic pain patients. In 2009 and 2010, more of the chronic pain cohort used publicly funded healthcare. In 2009, Maine residents utilized Medicaid at the third highest rate in the country [
51]. This increase indicates that a need for government assistance corresponds with the economic crash of 2008, which resulted in an increased number of Maine residents filing for unemployment; possibly exacerbating any chronic pain conditions, as it is known that distress experienced by unemployment, regardless of education, only increases likelihood of chronic pain development and the duration of the episode [
4,
7,
9,
27,
40,
52]
. Furthermore, the longer a person is out of work from chronic pain, the less likely they are to return back to work [
53]. Tian et al. (2013), also observed that more chronic pain patients were receiving Medicaid benefits than non-chronic pain patients within the same treatment facility [
28]. In addition, Maine has higher usage rates of public assistance compared to other states. Thus, these findings emphasize the importance of addressing the issue of chronic pain in the state, because chronic pain conditions could lead to more healthcare-associated costs, decrease a person’s ability to work, and increase the need for government assistance due to this loss of work.