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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
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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,