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Elevated detection thresholds for mechanical stimuli in chronic pain patients: support for a central mechanism.

OBJECTIVE
To investigate the relation between pain provoking cervical segments identified by diagnostic dorsal root blockades and elevation of detection thresholds in patients suffering from chronic cervicobrachialgia (CCB).


DESIGN
Quantitative sensory testing (light touch) of the cervical dermatomes using Semmes-Weinstein monofilaments.


SETTING
A university pain clinic.


SUBJECTS
Thirty-nine patients with CCB, with no clinical or diagnostic evidence of radiculopathy or surgically treatable bony lesion and with one main pain-provoking cervical segment identified by diagnostic dorsal root blockades.


OUTCOME MEASURES
Detection thresholds with 95% confidence intervals (95% CI) of pain-provoking segments, compared with surrounding and contralateral segments and with normal values for cervical dermatomes.


RESULTS
Patients' detection thresholds were significantly (p < .001) higher than those for normal subjects: 3.51 (95% CI, 2.71-4.31) and 3.10 (95% CI, 2.34-3.86), respectively. No significant differences existed between the segments. The elevations were systematic. However, thresholds on the painful side were consistently, slightly higher than those on the contralateral side.


CONCLUSION
Supporting earlier studies, results from CCB patients in the present study showed systematic elevation of detection thresholds (low threshold mechanoreceptors), an adaptation in contrast with, but not contradictory to, central sensitization of high threshold neurons in chronic pain.