The present study investigated the neuropathic components of chronic low back pain (LBP) in patients with and without lower limb pain using the DN4 questionnaire and confirmed its psychometric properties. Patients (n = 132) from 11 French multidisciplinary pain or rheumatology centers were classified by a first investigator into 4 groups derived from the Quebec Task Force Classification of Spinal Disorders (QTFSD): group 1 (pain restricted to the lumbar area); group 2 (pain radiating proximally); group 3 (pain radiating below the knee without neurologic signs); and group 4 (pain radiating towards the foot in a dermatomal distribution, with neurological signs, corresponding to typical radiculopathy). A second investigator applied the DN4 questionnaire to the lower limb (groups 2 to 4) and lower back. A comparison of groups 1 and 4 confirmed the psychometric properties of DN4 (sensitivity 80%; specificity 92%, for a cutoff of 4/10, similar to other neuropathic conditions). In the lower limb, the proportion of patients with neuropathic pain (NP) was related to the distality of pain radiation (15, 39, and 80% in groups 2, 3 and 4, respectively; P < .0001). In the lower back, the proportion of patients with NP was higher for patients with typical radicular pain compared with the other groups (P = .006). Thus, typical radiculopathy has similar characteristics as other neuropathic conditions and is confirmed as the commonest neuropathic syndrome in LBP patients. The observation that neuropathic and nociceptive components of LBP vary in the back and lower limb probably accounts for the discrepancies of reported prevalence rates of NP in LBP. As this study was essentially based on a questionnaire, future studies combining standard clinical sensory testing, specific questionnaires, and more objective assessment of the sensory lesion are now required to further investigate the neuropathic component of chronic LBP.

This study confirms the psychometric properties of the DN4 questionnaire to assess neuropathic pain in patients with low back pain. Neuropathic mechanisms largely contribute to pain in the lower limb as compared to the back, but neuropathic pain is not restricted to typical radiculopathy. This may have significant implications for the choice of treatment strategy in these patients.