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

Objective: To investigate the relation between pain provoking cervical segm ents identified by diagnostic dorsal root blockades and elevation of detect ion thresholds in patients suffering from chronic cervicobrachialgia (CCB). Design: Quantitative sensory testing (light touch) of the cervical dermatom es using Semmes-Weinstein monofilaments. Setting: A university pain clinic. Subjects: Thirty-nine patients with CCB, with no clinical or diagnostic evi dence of radiculopathy or surgically treatable bony lesion and with one mai n pain-provoking cervical segment identified by diagnostic dorsal root bloc kades. Outcome Measures: Detection thresholds with 95% confidence intervals (95% C I) 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) highe r 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 painfu l side were consistently, slightly higher than those on the contralateral s ide. Conclusion: Supporting earlier studies, results from CCB patients in the pr esent study showed systematic elevation of detection thresholds (low thresh old mechanoreceptors), an adaptation in contrast with, but not contradictor y to, central sensitization of high threshold neurons in chronic pain.