Medscape, LLC is pleased to provide online continuing medical education (CME) for this journal article, allowing clinicians the opportunity to earn CME credit.

This activity has been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education through the joint sponsorship of Medscape, LLC and Preventing Chronic Disease. Medscape, LLC is accredited by the ACCME to provide continuing medical education for physicians.

Medscape, LLC designates this Journal-based CME activity for a maximum of 1 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

All other clinicians completing this activity will be issued a certificate of participation. To participate in this journal CME activity: (1) review the learning objectives and author disclosures; (2) study the education content; (3) take the post-test with a 70% minimum passing score and complete the evaluation at www.medscape.org/journal/pcd (4) view/print certificate.

Release date: Febuary 27, 2014; Expiration date: February 27, 2014

Chronic pain is a common condition that affects one-third of the population in Europe and 12% of the Spanish population, accounting for a large number of medical consultations and a significant proportion of health care costs (1). Chronic pain is linked to several pathologies, such as rheumatic diseases (2), although other conditions, such as neck or back pain and migraine or other headaches, are common causes of chronic pain in the general population (3,4).

Disability is also a prevalent condition, affecting 8.9% of the Spanish population (5), and chronic pain is a common complaint in such patients (6). Osteoarthritis represents the main cause of physical disability (7) and chronic pain (1) in Spain. However, to our knowledge, the prevalence of other diseases that cause chronic pain, such as neck or back pain and migraine or other headache, has not been analyzed in people with disability. Thompson et al (8) emphasize the need to understand the factors that are related to pain in people with disability to find alternative treatments for reducing their levels of disability.

Evidence suggests that anxiety and depression are associated with increased pain sensitivity and pain-related disability (9), comorbid states that are more disabling than either condition alone (10). Likewise, sleep disorders have also been linked with chronic pain, and people who experience pain-related sleep disturbances are significantly more disabled than those who do not (11).

The objective of this study was to investigate the prevalence of painful musculoskeletal conditions and migraine or other headache and their link with anxiety, depression, and sleep disorders in a sample of Spanish adults with disability.

Although some studies have analyzed the prevalence of musculoskeletal pain and migraine or other headache among the general Spanish population, this is the first study, to the best of our knowledge, to investigate the prevalence of these painful conditions and their association with anxiety, depression, and sleep disorders in a population of adults with disability in Spain. Improving the knowledge of pain and its related factors in this population could contribute to finding alternative treatments for reducing levels of disability and improving quality of life.

A key finding in our study was the high prevalence of painful conditions among people with disabilities, especially rheumatic diseases. We found especially high rates of painful conditions among women aged 65 or older, those diagnosed with anxiety or depression, and those who slept 6 hours or less per day. We also observed a high prevalence of neck and back pain and migraine or other headache, a phenomenon not described previously in a population with disability.

The prevalences found in our study are consistent with but higher than the prevalences found in populations without disability in Spain. In this latter population, the 1-year prevalence of neck pain and lower back pain is approximately 20% (3), compared with 51% in our study, and the prevalence of migraine or other headache is 11% (4), compared with 23% in our study. Our findings also agree with those of a study that demonstrated that people with disabilities report a higher prevalence of pain, depression, anxiety, and worse quality of life (15). The higher prevalence among women and among the older age groups is consistent with the prevalence among the general population and can be partially explained by the longer life expectancy of women and the increased frequency of conditions that potentially cause pain in older populations (7,16). In a study assessing sex differences in pain-related disability among patients with musculoskeletal pain, women reported a greater intensity of pain and pain-related disability than men, even after controlling for depression, anxiety, and other psychological variables such as self-efficacy (17). Biological and psychosocial influences may predispose men and women to use different coping strategies and cause women to catastrophize more than men (18). A review of sex, gender, and pain described differences in clinical and experimental pain responses between men and women and discussed multiple mechanisms that may contribute to these differences, including gonadal hormones, endogenous pain modulating systems, gender roles, and cognitive/affective factors (19). Despite these considerations, contradictory findings suggest that disability is more directly related to pain in men than in women (20). Such inconclusive results support the need for further research into the sex and gender differences in people with pain and disability to foster future interventions to reduce disparities.

The association described here between painful conditions and anxiety or depression has been addressed in clinical settings and population-based studies (21,22). In these populations, negative emotional factors play an important role in the perception and experience of pain, and pain intensity is consistently documented as a predictor of physical disability and depression (23). The relationship between chronic pain and depression or anxiety is complex, and according to some researchers, reciprocal (24). However, the mechanisms that associate depression and anxiety with increased sensitivity to pain and greater disability remain poorly understood (9). Our group recently demonstrated the responsibility of the locus coeruleus in the onset of depression and anxiety as a consequence of chronic pain (25).

A synergistic effect of mental–physical comorbidity on severe disability has been reported (26), and mechanisms for this synergy have been proposed, including the possibility that depression exacerbates the disabling effect of a chronic physical condition by influencing treatment adherence and healthy behavior (27). Depression can also interfere with the psychological capacity to adjust to physical conditions, and it can affect the perception and appraisal of pain and the ability to cope with it (28).

The stronger link between depression and disability (both physical and mental) in women than in men further complicates the aforementioned relationships, suggesting that depression may have a greater disabling effect on women who suffer from pain (9). Anxiety has also been proposed to potentially mediate the sex differences in pain sensitivity; women tend to report higher levels of anxiety and are more likely to have anxiety disorders. However, increasing evidence suggests that anxiety is more strongly associated with pain responses in men than in women (29), and inconsistent or contradictory results have been reported on the direction of the link between anxiety and chronic pain within sexes and across outcome measures (18). In our study, the association between anxiety and painful conditions was independent of sex, unlike depression.

The link between sleep disorders and painful conditions described in our study is consistent with results reported for people who have pain but no disability; several authors suggest that the link between sleep disturbances and painful conditions is reciprocal (30). In the general population, chronic pain is associated with more symptoms of insomnia, more severe daytime consequences, and more chronic insomnia, thereby playing a major role in the chronicity of insomnia (11).

Our study has several limitations. The main limitation is the use of secondary data obtained for other purposes. The data on rheumatic diseases were not collected individually, and thus disaggregated analysis could not be performed. Also, because of missing values, we were unable to analyze data according to the survey participant’s exact type of disability. Despite these limitations, our study sheds light on the factors associated with the most common painful conditions found in people with disabilities, which to date has received little attention from researchers in Spain.

Our study also had strengths. A key strength is the large sample size and the inclusion of a group of people who have a disability but no pain, who are not typically included in studies. The inclusion of this group provides a broader perspective on the factors related to painful musculoskeletal conditions and migraine or other headache in people who have a disability. Moreover, the representativeness of the sample and the high response rate imply that the results are extendible to all people with disabilities in Spain.

Our study demonstrated that the prevalence of certain painful conditions — rheumatic diseases, neck and back pain, and migraine or other headache — is higher in people who have disabilities and that these conditions often co-exist with depression, anxiety, and sleep disorders. These findings suggest that pain-related conditions and their associated disorders should be considered in the design of pain-management programs to rehabilitate patients and improve their quality of life. Our study also reinforces from a translational perspective preclinical data that demonstrate a relationship between chronic pain and mental status.