Tactile thresholds are preserved yet complex sensory function is impaired over the lumbar spine of chronic non-specific low back pain patients: a preliminary investigation

ObjectivesTo investigate impairments in sensory function in chronic non-specific low back pain patients, and the relationship between any impairment and the clinical features of the condition.DesignA cross-sectional case–control study.SettingLaboratory-based study.ParticipantsNineteen chronic non-specific low back pain patients and 19 healthy controls.Main outcome measuresTactile threshold, two-point discrimination distance and accuracy at a task involving recognising letters drawn over the skin of the lower back (graphaesthesia) were assessed over the lumbar spine in both groups. Pain duration, pain intensity, physical function, anxiety and depression were assessed by questionnaire in the back pain group.ResultsNo difference was found in tactile threshold between the two groups [median difference 0.0 mg, 95% confidence interval (CI) −0.04 to 0.04]. There was a significant difference between controls and back pain patients for two-point discrimination (mean difference 17.9 mm, 95% CI 5.9 to 29.8) and graphaesthesia accuracy (mean difference 6.1, 95% CI 1.3 to 11.0). Low back pain patients had a larger lumbar two-point discrimination distance threshold and a greater letter recognition error rate. In the back pain group, no relationship was found between clinical profile and sensory function, and no relationship was found between the sensory tests.ConclusionsThese data support existing findings of perceptual abnormalities in chronic non-specific low back pain patients, and are suggestive of cortical rather than peripheral sensory dysfunction. Amelioration of these abnormalities may present a target for therapeutic intervention.