The late whiplash syndrome: a psychophysical study.
Some patients who have sustained whiplash injuries present with chronic widespread pain and mechanical allodynia. This single-blind, case control matched study of 43 chronic whiplash patients sought to examine psychophysical responses to non-noxious stimuli and their relationship to psychological profiles. Symptom Check List 90-R (SCL-90-R), Neck Disability Index and Shortform McGill Questionnaire were completed prior to testing. Qualitative stimuli comprised light touch, punctate pressure, moderate heat and cold. Additionally, sustained vibration was administered using a vibrameter which allowed ramping of either frequency or amplitude. Twenty-eight patients reported vibration-induced pain. No control subject experienced pain in response to vibration. No significant differences in perception threshold to vibration were noted between patients and control group. Twenty-three patients and ten control subjects reported painful responses to cold. Eleven patients and nine control subjects experienced pain in response to moderate heat. Four patients rated punctate pressure and one patient rated light touch as painful. SCL-90-R profiles revealed an overall elevated level of distress in the whiplash group. No significant difference was found between patients with and without vibration-induced pain for any dimension of the SCL-90-R. Pain in response to non-noxious stimulation over presumably healthy tissues suggests that central mechanisms are responsible for ongoing pain in at least some whiplash patients. The additional findings of pain on punctate pressure and hyperalgesic responses to heat and cold stimuli are consistent with enhanced central responsiveness to nociceptor input. These results have important therapeutic and prognostic implications.