Predictors of chronic pain
189
Table IV. Baseline predictors (T0) for pain sensitivity (Pain Sensitivity Questionnaire (PSQ)) at 2-year follow-up (T1)
Multivariable 1
Multivariable 2
(N=9,880; 13.3% missing data) * (N=8,873; 22.1% missing data) *
Univariable
Baseline predictors
Estimate (B) 95% CI
p-value
Estimate (B) 95% CI
Pain intensity 0.16 0.14, 0.18 < 0.001 Pain spreading a
Pain sensitivity
Age, years 0.21
0.72
0.05 0.19, 0.24 < 0.001
0.70, 0.73 < 0.001
0.02, 0.07 < 0.001 –
–
–0.03 –
–
–0.07,
0.16 0.10, 0.21 < 0.001 0.11 0.06,
0.05 0.02, 0.08 < 0.001 0.01 –0.04,
–0.17 –0.21, –0.14 < 0.001 –0.14 0.19 0.14, 0.27 < 0.001 0.03 0.79 0.69, 0.89 < 0.001 0.64 0.53,
0.52
–0.11 0.32, 0.72 < 0.001
–0.13, –0.08 < 0.001 –
–0.03
Sex (female/male b )
Marital status (married/other 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
b
Traumatic injuries (yes/no )
–
– 0.02
0.72
0.03
0.074
–0.03, 0.02
p-value
0.089
–0.02, 0.06 0.391
0.69, 0.74 < 0.001
–0.04, 0.09 0.420
0.17 < 0.001 0.02 –0.03, 0.06 0.484
0.05 0.03 –0.02, 0.08 0.310
–0.18, –0.10 < 0.001 –0.01 –0.06, 0.04 0.714
–0.03, –0.03, 0.13 0.246
0.10
0.807
0.330
0.05
0.75 < 0.001
–
–0.05, 0.01
0.28
–
0.070 –
–0.01
– –
0.16, 0.40 < 0.001
–
–0.04, 0.02
– 0.07, 0.22 < 0.001 –0.02 Pulmonary disorders (yes/no b ) 0.18 0.12, 0.4 < 0.001 0.03 –0.04, 0.11 0.373 –0.02 –0.09, 0.06 0.665
0.16 0.07, 0.25 < 0.001 –0.03 –0.12, 0.07 0.654 –0.03 –0.12, 0.07 0.662
Disorders of the CNS (yes/no b ) 0.27 0.20, 0.35 < 0.001 0.13 0.05, 0.21 0.001 0.03 –0.06, 0.11 0.506
0.20 0.13, 0.26 < 0.001 0.07 –0.01, 0.14 0.062 –0.01 –0.08, 0.07 0.936
0.35 0.22, 0.47 < 0.001 0.16 0.02, 0.30 0.025 –0.06 –0.19, 0.08 0.419
0.10 0.02, 0.18 0.014 0.04 –0.05, 0.13 0.358 0.02 –0.08, 0.11 0.724
–0.07, 0.26 0.188 0.17 –0.01, 0.34 0.067
Skin diseases (yes/no b )
Tumours/cancer (yes/no b )
–
–
0.486
0.14
Urogenital disorders (yes/no b )
0.217
–0.02
–
Gastrointestinal disorders (yes/no b )
0.15
0.03
– 0.24, 0.37 < 0.001
Cardiovascular disorders (yes/no b )
–0.03,
p-value Estimate (B) 95% CI
–
0.31
Rheumatoid arthritis/osteoarthritis (yes/no b )
0.06
–
–0.09, 0.05
–
0.518
0.24 0.09, 0.38 0.002 0.09 Depression (yes/no b ) 0.36 0.27, 0.45 < 0.001 0.25 0.15, 0.35 < 0.001 0.13 0.03, 0.22 0.014
0.41 0.32, 0.48 < 0.001 0.25 0.16, 0.33 < 0.001 –0.02 –0.12, 0.08 0.662
Anxiety (yes/no ) 0.41 0.34, 0.49 < 0.001 – –
Metabolic disorders (yes/no b )
b
–
–
–
–
*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.
B: unstandardized regression coefficient; CI: Wald confidence interval; 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.
pain intensity has been shown to predict increased pain
intensity (31, 42) and to predict CP (single characte-
ristics of pain not presented) (43). Spread of pain was
associated with CP (single characteristics of pain not
presented) at follow-up (44, 45) and anatomical spread
of pain at follow-up (46, 47). In non-longitudinal stu-
dies, spread of pain has been found to be significantly
correlated with pain intensity (48, 49). In a systematic
review, both pain spread and intensity were considered
prognostic factors for CP (single pain characteristics
not presented) (50). The multivariable models 2 in
the current study provides a comprehensive overview
on the impact of 3 characteristics of pain (intensity,
spread and sensitivity) on the burden of pain over time.
Based on the results of the present study and the above
studies, future longitudinal studies should investigate
risk factors for several characteristics of pain and in-
clude these characteristics of pain at baseline in order
to predict accurately how pain develops.
Other longitudinal studies that tried to detect signi-
ficant predictors in relation to CP thus restricted their
analysis mostly to 1 characteristic of pain or to a general
label of pain. As argued in the introduction, such a uni-
dimensional approach is from a clinical point of view
a too simplistic description of pain per se. To the best
of our knowledge, this study is the first comprehensive
attempt to ascertain predictors of different common
clinical characteristics of CP in the light of the concept
and perception of pain as a multifaceted phenomenon.
The results of the current study highlight that the features
of the predictors in the final models are only to a limited
extent common for the 3 characteristics of pain investi-
gated. Furthermore, this study suggests that CP, as most
often defined and as defined in this study, constitutes
a general indicator for several clinical characteristics
of CP. It appears that characteristics of pain, such as
intensity, anatomical spread, and sensitivity, only partly
reflect similar underlying neurobiological mechanisms
both in the cross-sectional and longitudinal perspec-
tives. Hence, recent cross-sectional studies of muscle
and plasma in patients with CP conditions have shown
that pain intensity and pain sensitivity (i.e. pressure
pain thresholds) are associated with different molecular
mechanisms from a protein pattern perspective (51, 52).
Moreover, the characteristics of pain investigated may
be, at least partly, processed differently in the CNS and
have different associations with other conditions, such
as psychological symptoms.
The current longitudinal results confirm the results
of previous (mostly cross-sectional) studies, sugges-
ting associations between sociodemographic factors
and single characteristics of pain (1, 15, 16, 53–55)
and that such factors are less predictive of short- to
medium-term changes in pain.
The present longitudinal study found being female to
be a predictor for pain intensity (Table II, multivariable
J Rehabil Med 51, 2019