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 low back pain (CPLP). Non-invasive functional near-infrared spectroscopy (fNIRS) was employed to detect spinal cord dysfunctions by recording perispinal neurovascular response (NVR). Approach: In a prospective study of 92 CPLP patients and 65 healthy age-matched volunteers, the pain maps, Visual analog scale, body mass index, posterior tibial nerve conduction velocity (NCV), and lumbar and cervical NVRs triggered by non-noxious electrical stimulation of this nerve were assessed. Main results: CPLP patients showed a 60.58% lower NVR amplitude at the cervical level compared to the controls, with no significant difference at the lumbar level. The NVR rise time was 44.25% and 33.29% lower in cervical and lumbar recordings, respectively, in CPLP patients compared to controls, with no significant difference in NVR duration. 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 (ptextless0.05). Additionally, BMI showed a negative correlation with all NVR parameters at both recording sites in CPLP patients, but not in controls (p textless 0.05). Significance: 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 dysfunctions. For the first time, perispinal NVR dysfunction is reported in CPLP patients, suggesting an altered descending modulation at the lumbar spinal cord.