Journal of Rehabilitation Medicine 51-3 | Page 42

188 B. Larsson et al. Table III. Baseline predictors (T0) for pain spreading (NP, LP, RP-Medium, RP-Heavy, and WSP) at 2-year follow-up (T1) treated as an ordinal outcome Multivariable 1 Multivariable 2 (n = 8,860; 22.2% missing data)* (n = 7,874; 30.8% missing data)* Univariable Baseline predictors Estimate (OR) 95% CI Pain intensity 1.31 1.27, 1.34 < 0.001 – – – 1.15 1.11, 1.19 < 0.001 Pain spreading a Pain sensitivity Age, years 4.09 1.21 1.15 3.92, 4.27 < 0.001 1.17, 1.24 < 0.001 1.12, 1.19 < 0.001 – – 0.95 – – 0.90, 1.01 – – 0.065 2.93 1.04 0.99 2.69, 3.18 < 0.001 1.01, 1.08 0.041 0.92, 1.08 0.944 Marital status (married/other b ) 1.77 1.65, 1.90 < 0.001 1.70 1.56, 1.84 < 0.001 1.46 1.30, 1.65 < 0.001 1.18 1.12, 1.23 < 0.001 1.00 0.94, 1.06 0.93 0.86, 1.02 0.099 0.80 0.77, 0.84 < 0.001 0.86 0.84, 0.94 < 0.001 0.98 0.90, 1.06 0.979 1.24 1.15, 1.33 < 0.001 0.76 0.69, 0.84 < 0.001 0.94 0.81, 1.08 0.402 1.47 1.29, 1.67 < 0.001 1.33 1.15, 1.55 < 0.001 0.95 0.77, 1.18 0.952 0.96 0.87 0.74, 1.26 0.785 0.84, 0.89 < 0.001 – 0.97 – 0.94, 1.01 – 0.97 – 0.91, 1.02 – 0.966 Sex (female/male b ) Educational level (university/other b ) Employment (unemployed/employed b ) Country of birth (abroad/Sweden b ) Citizenship (other/Sweden b ) Household income, Euros per year Traumatic injuries (yes/no b ) p-value p-value 0.976 – 0.165 Estimate (OR) 95% CI p-value Rheumatoid arthritis/osteoarthritis (yes/no b ) 4.26 Cardiovascular disorders 1.55 3.15, 3.96 < 0.001 2.74 2.41, 3.12 < 0.001 1.59 1.36, 1.85 < 0.001 3.90, 4.65 < 0.001 1.43, 1.68 < 0.001 3.49 1.21 3.14, 3.86 < 0.001 1.09, 1.35 < 0.001 1.50 0.94 1.31, 1.71 < 0.001 0.82, 1.08 0.401 Pulmonary disorders (yes/no ) 1.76 1.57, 1.97 < 0.001 1.13 0.98, 1.27 1.02 0.86, 1.22 2.71 2.46, 2.98 < 0.001 1.85 1.66, 2.05 < 0.001 1.40 1.21, 1.61 < 0.001 2.11 1.94, 2.30 < 0.001 1.54 1.39, 1.71 < 0.001 1.14 1.00, 1.31 Skin diseases (yes/no b ) 1.83 1.55, 2.14 < 0.001 1.19 0.98, 1.45 1.05 0.81, 1.34 0.735 1.57 1.41, 1.74 < 0.001 1.23 1.09, 1.38 < 0.001 1.12 0.95, 1.32 0.186 Metabolic disorders (yes/no b ) 1.42 1.18, 1.71 < 0.001 0.93 0.73, 1.17 1.92 1.72, 2.15 < 0.001 1.31 1.15, 1.49 < 0.001 Anxiety (yes/no b ) 2.54 2.29, 2.82 < 0.001 1.82 1.62, 2.05 < 0.001 1.15 0.98, 1.34 0.081 2.28 2.07, 2.51 < 0.001 – – – – – 3.53 b Gastrointestinal disorders (yes/no b ) Disorders of the CNS (yes/no b ) Urogenital disorders (yes/no b ) Tumours/cancer (yes/no b ) Depression (yes/no b ) 0.084 0.075 0.533 – 0.807 0.048 0.91 0.66, 1.25 0.910 1.13 0.95, 1.34 0.169 * n  = number of complete cases included in the models out of a total of 11,386 respondents. a Baseline spread of pain was entered to the models as covariate with 5 levels 0=no pain, 1=local pain, 2=Regional Pain-Medium, 3=Regional Pain-Heavy, and 4=widespread pain. b Reference category. OR: Odds ratio; CI: Wald confidence interval; NP: No pain; LP: Local pain; RP-Medium: Regional pain medium; RP-Heavy: Regional pain heavy; WSP: widespread pain; CNS: central nervous system; Multivariable 1: all baseline variables together in 1 model without baseline pain dimensions; Multivariable 2: all baseline variables from multivariable model 1, including baseline pain dimensions. Significant differences in bold. Predicting pain sensitivity at T1 The univariable and multivariable analyses are presen- ted in Table IV. The univariate analysis showed that all the examined variables at T0, except for traumatic inju- ries, had p-values below 0.05 in their associations with pain sensitivity at T1 (all p < 0.05). In the multivariable analysis without the pain, characteristics at T0 included female, immigrant, RA/OA, pulmonary, GI, urogenital, and metabolic disorders, and were positive significant predictors (Table IV; multivariable model 1). When the 3 pain characteristics at T0 were intro- duced as predictors, only pain sensitivity at T0 was a positive significant predictor of pain sensitivity at T1 (Table IV; multivariable model 2). Only immigrant and metabolic disorders remained as positive significant predictors. The results of the current study regarding all 3 outcome variables remained to a great degree when the spread of pain at T0 was used as an ordinal cova- riate in a subsequent sensitivity analysis (Table SII 1 ). DISCUSSION Estimate (OR) 95% CI Several socio-demographic features and comorbidities at T0 were significant predictors of pain intensity, spread and sensitivity 2 years later (T1). When the pain characteristics at T0 (i.e. intensity, spread and www.medicaljournals.se/jrm sensitivity) were included, these were relatively strong significant predictors of intensity and spread at T1. After that adjustment, both socio-demographic and comorbidity predictors were substantially fewer and for those significant predictors their effect estimates had generally decreased. It is notable that being female and traumatic injuries were likewise significant pre- dictors, together with the 3 pain characteristics, for pain intensity and spread at T1; unique predictors (education level and being an immigrant) also existed for these 2 pain characteristics. Pain sensitivity was the only characteristic of pain at T0, and being an immigrant and metabolic disorders that significantly predicted sensitivity at T1. It should be stressed that the inclusion of pain cha- racteristics at baseline changes the interpretation of the model from a prediction of pain at T1 (multivari- able model 1) to a prediction of the change in pain at T1 (multivariable model 2). The results indicate that socioeconomic factors and comorbidities were more common and stronger risk factors for the cumulative burden of pain than for changes during the medium- to short-term. The results also indicate that current pain intensity, anatomical spread, and sensitivity strongly influence the course of CP intensity and spread. The im- pact of single pain characteristics on the burden of pain over time has been reported previously. For example,