Changes in Pain Sensitivity and Conditioned Pain Modulation During Recovery from Whiplash Associated Disorders

OBJECTIVES: To investigate the pain-sensory profile of patients with whiplash-associated disorders (WAD) prior and post 2-weeks of standardized rehabilitation and after at 6-months follow-up.

METHODS: Twenty-two WAD-participants (Grade-II; 14 women) and 22 sex-and age-matched healthy controls were enrolled. Pressure pain thresholds (PPTs) were assessed at local and distal muscles. Conditioned pain modulation (CPM) of PPTs was assessed using cuff-pressure around the upper-arm. Referred area of pain following supra-threshold pressure stimulation of the infraspinatus muscle was recorded on a body chart. Psychometric variables (Pain intensity, area of perceived pain, pain catastrophizing, kinesiophobia, sleep problems, depression level) were assessed. WAD-group additionally completed the Neck Disability Index (NDI).

RESULTS: The WAD-group demonstrated lower local PPTs compared to controls at all timepoints (P<0.05) and lower distal PPTs at baseline and at 2 weeks when compared to 6-months (within-group) (P<0.05). The WAD-group had a reduced CPM response and larger induced referred pain areas compared to controls (P<0.05), while no within-group changes were observed at any time point. The WAD-group reported higher pain intensity and perceived area of pain compared to controls at all timepoints (P<0.05) and a mean NDI-score of 41% at baseline, 16% at 2-weeks, and 4% at 6-months. Furthermore, the WAD-group reported improvements in all other psychometric variables (P<0.05), although only pain catastrophizing levels were comparable to controls at 2-weeks.

DISCUSSION: PPTs but not CPM improved in the WAD-group and were comparable to controls following 2-weeks following standardized rehabilitation, indicating that normalization of CPM may not be required to recover from WAD.