Pain characteristic differences between subacute and chronic back pain

Abstract

Back pain is commonly classified based on duration. There is currently limited information regarding differences in the clinical features of back pain between these duration-based groupings. Here, we compared the pain characteristics of patients with subacute (SBP; pain 6-16 weeks, n = 40) and chronic back pain (CBP; pain ≥1 year, n = 37) recruited from the general population. CBP patients reported significantly higher pain intensity on the Visual Analogue Scale (VAS) compared to SBP patients. Based on this finding, we investigated group differences and their dependence on VAS for the Beck Depression Inventory (BDI), sensory and affective dimensions of the McGill Pain Questionnaire (MPQ-S and MPQ-A), Neuropathic Pain Scale (NPS), and the variability of spontaneous pain. Correction for VAS abolished significant group differences on the MPQ-S, MPQ-A and NPS. Only a significant difference in the variability of spontaneous pain was independent of VAS. Finally, whereas SBP patients displayed a higher incidence of unilateral pain radiating down the legs/buttocks, there was a shift towards more bilateral pain in CBP patients. In summary, SBP and CBP groups differ on 3 independent parameters: VAS ratings, pain location, and temporal dynamics of spontaneous pain.

Perspective: The present study reports differences in the characteristics of back pain between duration-based groupings in the general population. The main outcome of the study is the demonstration that a small number of descriptors are required to characterize the difference between SBP and CBP.

Figure 1. Differences in sensory and affective dimensions between SBP and CBP failed to survive correction for pain intensity

(a) CBP patients displayed a robust increase in VAS ratings compared to SBP patients. In graphs b–f, we present the mean total scores for the (b) BDI (c) MPQ-S and (d) MPQ-A, (e) NPS and (f) fractal dimension both uncorrected (left) and corrected for VAS rating (right). Before correction for VAS, patients with CBP had significantly higher ratings for MPQ-S, MPQ-A, NPS and lower fractal dimension. Only the significant increase in fractal dimension survived correction, indicating that variability of spontaneous pain is the sole parameter independent of VAS. Bars represent mean ± S.E.M. (n=32–40). *p<0.05; ***p<0.001; ****p<0.0001.

Figure 2. Group differences in scores for sensory and affective pain questionnaire items were abolished by correction for pain intensity

We investigated differences between SBP and CBP in the individual questionnaire items related to the sensory and affective dimensions of pain. Here, we present the mean scores for each questionnaire item of the (a) MPQ- S (b), MPQ-A and (c) NPS, both uncorrected (left) and corrected for VAS ratings (right). Patients with CBP had higher uncorrected scores on nine questionnaire items (six MPQ-S, three MPQ-A, three NPS items). After correction for VAS, the majority of these significant group differences were abolished. Bars represent mean ± S.E.M. (n=37–40). *p<0.05; **p<0.01; ***p<0.001.

Figure 3. Evidence of a shift in the laterality of pain during the transition from SBP to CBP

We characterized pain location based on the body regions that patients had shaded in with pencil on the MPQ form. (a) The body was divided into six sections on the left and right side. (b) We conducted separate between-groups comparisons at each of the twelve body sites, and found that the incidence of reported pain did not differ between SBP and CBP groups for any of the regions. (c) Pain radiating down the legs and/or buttocks (i.e. pain in ≥1 of regions 2–5) was more frequently unilateral in SBP patients, and more bilateral among CBP patients. Bars represent mean ± S.E.M. (n=37–40). *** p<0.001