DIFFERENTIAL ELECTROMYOGRAPHIC RESPONSE TO EXPERIMENTAL COLD PRESSOR TEST IN CHRONIC LOW-BACK-PAIN PATIENTS AND NORMAL CONTROLS

Objectives. To identify painful stressor-induced surface electromyogra phy [sEMG] responses in chronic low back pain [CLBP] patients and pain -free controls to experimental noxious stimulation, the cold presser t est [CPT] and investigate potential differences in pain report. Method s. Fourteen CLBP patients and 12 age/gender matched controls underwent an identical sEMG recording protocol in six stages: baseline, hand in 15 degrees C cool water, a recovery period, a CPT, a second recovery phase and a post-test evaluation. Surface electromyography was recorde d at bilateral trapezius, and paraspinal sites at L5. Results. Across all stages of the experiment there was no statistically significant di fference in pain report. However, following the experiment patients re ported significantly higher retrospective pain ratings than the contro ls using the Short Form-McGill Pain Questionnaire [SF-MPQ]. During bas eline conditions, no differences in sEMG were noted between the groups . During the cool water condition, patients showed increased L5 sEMG i n the left side compared to controls. Patients' elevated sEMG persiste d after the hand was taken out of the cool water and increased further during the CPT. These group differences occurred for both sides and w ere most marked on the contralateral side to hand immersion. The incre ases on the ipsilateral side failed to reach significance. In contrast , the control subjects demonstrated increased sEMG activity in the tra pezius muscles across the testing stages but this only reached signifi cance for the right side. Conclusions. These results suggest a prefere ntial activation of the lumbar paraspinal muscle activation in CLBP pa tients during painful hand stimuli. In addition retrospective rating o f experimental pain by CLBP patients, using the SF-MPQ may be unrepres entative of the experimental condition.