Comorbidity Is Associated with Pain in Multiple Sclerosis
Objectives: To examine the relationship between comorbidity and pain in MS.
Methods: From July 2010-March 2011 we recruited consecutive patients with definite MS from four Canadian MS Clinics. Participants completed the Health Utilities Index (HUI-Mark III) and a validated comorbidity questionnaire at 3 visits over 2 years. The HUI’s 5-point utility-weighted pain scale was initially dichotomized into two clinically relevant groups: those with and without pain that disrupts normal activities. We used logistic regression to assess the association of pain with each comorbidity individually at baseline (as Odds Ratios [OR], with 95% Confidence Intervals [95% CI]), and over time. Secondly, changes in pain scores (5-point ordinal scale) between visits were modeled using a logistic model with generalized estimating equations (GEE) to better determine longitudinal within-person effects of comorbidity on pain. All models were adjusted for age, sex, time since symptom onset, disability (EDSS), and the presence of other comorbidities.
Results: Of 949 participants, most were female(75.2%) and white(85.4%), with a mean(SD) age of 48.6(11.4) years, and a relapsing-remitting course(72.4%). At baseline, 41.5% of participants had at least one comorbid health condition, and the prevalence of disruptive pain was 40.5%. The incidence of disruptive pain at years one and two were 12.1 and 12.7 per 100 persons, respectively. Significant baseline population-level effects on pain of peripheral vascular disease, fibromyalgia, rheumatoid arthritis, IBS, IBD, migraine, COPD, depression, anxiety, hypertension, and high cholesterol persisted at all time points (p<0.006). Significant individual-level effects on the presence of worsening pain were seen for bipolar disorder (OR: 3.05 95% CI: 1.32-7.05), lupus (OR: 2.82 95% CI: 1.26-6.29), COPD (OR: 1.50 95% CI: 1.08-2.09), anxiety (OR: 1.49 95% CI: 1.07-2.08), and autoimmune thyroid disease (OR: 1.40 95% CI: 1.00-1.97).
Conclusions: Pain is a concern for all persons with MS but more so for those with comorbidities. Closer examination of these associations may provide guidance for better management of these potentially disabling symptoms in persons with MS.