The P50 midlatency auditory evoked potential in patients with chronic low back pain (CLBP)

Patients with Chronic Low Back Pain (CLBP) show arousal, attentional and cognitive disturbances. The sleep state-dependent P50 midlatency auditory evoked potential was used to determine if patients with CLBP [with and without co-morbid depression (DEP)] show quantitative disturbances in the manifestation of the P50 potential.

P50 potential latency, amplitude and habituation to repetitive stimuli at 250, 500 and 1000ms interstimulus intervals (ISIs) was recorded, along with the McGill Pain Questionnaire-Short Form (MPQ-SF). CLBP subjects (n=42) were compared with Controls (n=43), and with subjects with DEP only (n=6). Of the CLBP subjects, 20/42 had clinical depression (CLBP+DEP); 8/20 were taking anti-depressant medication (CLBP+DEP+med), the others were not (CLBP+DEP-med).

There were no differences (ANOVA) in age, sex or P50 potential latency, although there was a trend towards increased latencies in CLBP groups. P50 potential amplitude was lower in CLBP groups, but not in sub-groups, again indicating a trend. P50 potential habituation was decreased in the DEP only subjects at the 250m ISI, and decreased in CLBP+DEP-med subjects at the 500ms ISI. This difference was not present in CLBP+DEP+med subjects. The MPQ-SF revealed that patients with CLBP and CLBP+DEP-med showed lower pain scores than CLBP+DEP+med patients.

There is decreased habituation of the P50 potential habituation in unmedicated patients with CLBP+DEP compared to Controls.

Patients with CLBP+DEP-med may be less able to disregard incoming sensory information, including painful sensations, but anti-depressant medications help correct this deficit. However, their perception of pain may be increased by medication.