Psychophysical evidence for a neuropathic component of chronic neck pain.

Recent studies into the common complaint of chronic neck pain have focused on its anatomical origin, identifying especially the cervical zygapophysial joints. However the pathophysiology of chronic neck pain remains poorly understood. In this psychophysical study, responses to electrocutaneous stimulation in subjects with chronic neck pain were examined. In an ascending method of limits design. electrical stimuli at 100 Hz with variation in current from 0 to 45 mA and in pulse width from 100 to 1000 micros were delivered transcutaneously to two points 2 cm from the midline bilaterally at the levels of C5/6 and C7/T1 in 35 subjects with chronic neck pain and 22 pain-free volunteers. There was a small difference in detection threshold between the two groups: both pain threshold and pain tolerance were significantly lower in the pain group compared with pain free controls. These findings define hyperalgesia psychophysically and, taken together with the absence of tissue damage at the sites of testing. suggest that these painful cervical regions may be examples of secondary hyperalgesia which, in turn, implies central sensitisation of nociceptive pathways. These results are compatible with studies which identify potential anatomical origins of chronic neck pain but provide evidence that central sensitisation may be the relevant mechanism of pain production.