Altered descending modulation in patients with chronic primary low back pain assessed by non-invasive functional near-infrared spectroscopy

<i>Objective</i>. Low back pain (LBP) is a significant public health issue. Despite current medical imaging and neurophysiological tests, up to 90% of patients lack a clear cause, leading to a diagnosis of chronic primary LBP (CPLP). Non-invasive functional near-infrared spectroscopy (fNIRS) was employed to detect spinal cord dysfunctions by recording perispinal neurovascular response (NVR).<i>Approach</i>. In a prospective study of 71 CPLP patients and 65 healthy age-matched volunteers, pain maps, visual analog scale (VAS), body mass index (BMI), posterior tibial nerve conduction velocity (NCV), and lumbar and cervical NVRs triggered by non-noxious electrical stimulation of this nerve were assessed.<i>Main results</i>. CPLP patients exhibited a 53.29% reduction in NVR amplitude at the cervical level compared to the controls, with no significant difference at the lumbar level. CPLP patients compared to controls show a rise time of 6.64% and 5.14% larger in cervical and lumbar recordings, respectively, but a duration of 10.11% and 5.32% shorter, respectively. Posterior tibial NCV was within normal clinical range in both groups. In CPLP patients, VAS scores were negatively correlated with NVR rise time, amplitude, and duration at the lumbar site, as well as with rise time and duration at the cervical site (<i>p</i>< 0.05). Additionally, BMI showed a negative correlation with all NVR parameters at both recording sites in CPLP patients, but not in controls (<i>p</i>< 0.05).<i>Significance</i>. This is the first report of perispinal NVR dysfunction in patients with CPLP. Its results suggest a loss of inhibitory regulation in the lumbar spinal cord in CPLP patients and demonstrate the potential of fNIRS to detect and quantify spinal cord neurovascular dysfunctions. For the first time, perispinal NVR dysfunction is reported in CPLP patients, suggesting an altered descending modulation system at the lumbar spinal cord.