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Prevalence of chronic pain among individuals with neurological conditions

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by Jacquelyn J. Cragg, Freda M. Warner, Matthew S. Shupler, Catherine R. Jutzeler, Neil Cashman, David G. T. Whitehurst and John K. Kramer

According to recent estimates, 6 million people in Canada (19% of the population)^{Note 1} and 25 million in the United States (11%)^{Note 2} report a form of chronic pain. Debilitating in the general population,^{Note 3} chronic pain among people with neurological conditions further reduces quality of life and increases the burden on the health care system.^{Note 4Note 5Note 6}

The prevalence of pain has been estimated separately for individuals with various neurological conditions, including spinal cord injury,^{Note 7Note 8Note 9} stroke, ^{Note 10Note 11Note 12} multiple sclerosis,^{Note 13Note 14Note 15} and Parkinson’s disease.^{Note 16Note 17Note 18} Pooling prevalence estimates across studies, which is necessary to accurately depict the overall burden of chronic pain in neurological conditions, is hampered by a lack of a unifying definition of pain. As well, the prevalence of chronic pain across neurological conditions is difficult to estimate without applying the same definition across studies. Both factors are important for planning health care services and training health care professionals to better manage chronic pain.

Based on a common definition of pain, this analysis estimates and compares the prevalence of chronic pain among household residents aged 15 or older within and between 16 neurological conditions.

Data and methods

Data source

The data are from the 2011/2012 Survey on Living with Neurological Conditions in Canada (SLNCC).^{Note 19Note 20Note 21} Ethics approval for the use of SLNCC data was obtained via the publicly available data clause from the University of British Columbia, in accordance with the Tri-Council Policy Statement.^{Note 22}

SLNCC participants were identified from the 2010/2011 Canadian Community Health Survey (CCHS),^{Note 23} a cross-sectional general population survey conducted by Statistics Canada. The CCHS included questions about neurological conditions; respondents who reported having been diagnosed with such conditions were selected for the SLNCC. These CCHS respondents were asked if members of their household had one or more of the same conditions; those identified were also selected to participate in the SLNCC.^{Note 23}

The estimated response rate for the 2010/2011 CCHS was 72%.^{Note 24} Among individuals reporting a neurological condition on the CCHS, the estimated response rate for completing a subsequent diagnosis module on the SLNCC was 82%.^{Note 23}

Trained interviewers obtained data from the community-dwelling population aged 15 or older in the 10 provinces. The interviews were conducted from September 2011 through March 2012. The SLNCC excluded people living in the territories, institutions, and reserves, and full-time members of the Canadian Forces. These exclusions represent less than 3% of the Canadian population.^{Note 23}

Selected neurological conditions and pain assessment

Neurological conditions were derived from self-reports (Text table 1). In addition to questions about diagnosed neurological conditions, three SLNCC questions pertained to pain,^{Note 25} one of which was chosen for this analysis: “Are you usually free of pain or discomfort?”

For this study, several exclusions from the SLNCC cohort (weighted estimate = 1,737,888) were necessary. To achieve mutually exclusive categories, respondents who reported a diagnosis of more than one neurological condition were omitted (220,995), as were those with missing values (“don’t know,” “refused to answer,” or “not stated”) for the pain question (43,493), and those with conditions with a sample size insufficient for logistic regression analyses (6,289). The final weighted study sample totalled 1,467,165.

Statistical analysis

Descriptive statistics (percentages and means) were used to present the prevalence of neurological conditions and demographic characteristics of respondents who reported having been diagnosed. Multivariable logistic regression was used to compare the odds of chronic pain (adjusting for age and sex) between neurological conditions.

Probability weighting accounted for the SLNCC survey sampling design. Survey weights were obtained by dividing the frequency weights provided by Statistics Canada (the number of people represented by the individual) by the average frequency weight for the given sample. Thus, the values are representative of sex and age groups in each health region. SAS statistical software (SAS Institute, Cary, NC, USA, Version 9.3) was used for all statistical analyses.

Results

In 2011/2012, close to 1.5 million household residents aged 15 or older reported having been diagnosed with a neurological condition. Their median age ranged from 25 among those with cerebral palsy to 80 among those with dementia (Table 1). Females made up 84% of people reporting migraine headaches. The lowest percentage of females—23%—was among those in the “other” category, which comprised amyotrophic lateral sclerosis, Tourette’s syndrome, and Huntington’s disease.

The prevalence of chronic pain among people with neurological conditions overall was 36% (95% CI: 31% to 42%) (Figure 1). The percentage reporting that they were not usually free of pain peaked at 84% among those with spinal cord trauma. As well, more than half of those with a brain tumour or dystonia reported chronic pain. Pain was least prevalent among people with epilepsy (25%).

The unadjusted odds of reporting chronic pain, relative to all the other neurological conditions combined, were significantly higher only among individuals with spinal cord trauma (10.7; CI = 3.4 to 30.4)(Table 2). When age and sex were taken into account, the odds were reduced, but remained significantly high (8.3; CI = 1.5 to 46.2).

Discussion

Pain has been extensively examined among people with various neurological conditions.^{Note 8Note 9Note 10Note 11Note 12Note 16Note 17Note 18Note 20Note 26Note 27Note 28Note 29Note 30} However, owing to differences in assessment and study methodology, pooled estimates and comparisons across conditions are nearly impossible. This is the first study to use a single pain question in a large sample with various neurological conditions, thereby permitting such an analysis. In response to a comprehensive and representative national survey, more than a third (36%) of people with neurological conditions reported that they were not usually free of pain.

The prevalence of pain reported by people with neurological conditions is about twice estimates for the general population (figures based on the same pain question range from 15% to 19%).^{Note 31} Although the SLNCC sample is older and contains a larger percentage of females, age and sex likely do not entirely account for this discrepancy. Contributing factors may include spasms (for example, cervical dystonia),^{Note 32} cancer (for example, brain tumours),^{Note 33} and paralysis (for example, post-stroke shoulder pain).^{Note 11} Depression associated with neurological conditions may also be associated with greater pain prevalence.^{Note 34}

The prevalence of chronic pain was highest—84%—among those with traumatic spinal cord damage. A defining feature of spinal cord trauma is central and peripheral neuropathic pain symptoms (42%),^{Note 30Note 35} as well as nociceptive musculoskeletal pain (71%).^{Note 35} Pain often emerges in the initial days after injury, increases in severity over time, and is problematic to manage.^{Note 35} Reliance on mobility devices such as wheelchairs and/or crutches can also result in musculoskeletal pain (for instance, shoulders).^{Note 9}

Strengths and limitations

A strength of this study is that pain prevalence is based on a single question answered by a large number of survey respondents with neurological conditions. Even so, the prevalence of pain among individuals with neurological conditions may be an underestimate, as the sample is community-based and does not include residents of institutions.

Another limitation is that the data were self-reported. Although self-report has been shown to be appropriate for the measurement of pain,^{Note 36} it has not been validated for the majority of neurological conditions (exceptions include stroke and migraine^{Note 37Note 38}). Self-report may be less valid in situations where proxy assessment is required and in conditions such as dementia that affect cognitive function.^{Note 39} Research suggests that self-reported diagnosis tends to be more valid for conditions with clear symptomatology and event history.^{Note 40} Therefore, several neurological conditions may have adequate validity (for example, spinal cord trauma). As well, the SLNCC interviewer notes attempted to clarify responses (for instance, “Do not include back pain if this is the only symptom of spinal cord injury”). Moreover, the age and sex distributions of the conditions generally match published literature (large percentage of females among those with migraine^{Note 20}; large percentage of males among those with traumatic spinal cord injury^{Note 7Note 35}).

Conclusion

Overall, more than a third of people with neurological conditions reported chronic pain. The high prevalence of chronic pain among individuals with spinal cord trauma indicates a need for targeted health services and for research to identify effective treatments options.

Acknowledgements

This work was supported by the Blusson Integrative Cures Partnership. Jacquelyn J. Cragg is supported by the Branco Weiss Fellowship-Society in Science and by the Michael Smith Foundation for Health Research (MSFHR). Freda M. Warner is the recipient of the University of British Columbia Four Year Fellowship. Catherine R. Jutzeler is supported by the International Foundation for Research in Paraplegia (IRP) Postdoctoral Fellowship. Matthew S. Shupler is supported by the Collaborative Research and Training Experience Atmospheric Aerosol Program, funded by the Natural Sciences and Engineering Research Council of Canada. John K. Kramer is a MSFHR and Rick Hansen Institute Scholar, and is also supported by Wings For Life, IRP and the Canadian Institutes of Health Research.