Screening for neuropathic characteristics in failed back surgery syndromes: challenges for guiding treatment.

Abstract

Neuropathic pain screening tools have shown promise in identifying common neuropathic pain characteristics that derive from diverse etiologies (e.g., diabetic peripheral neuropathy, postherpetic neuralgia). However, no prior studies have specifically assessed whether these tools are capable of discerning the underlying pain mechanisms in the vast, heterogeneous group of patients diagnosed with failed back surgery syndrome (FBSS). In this clinical observational study, two tests for neuropathic pain characteristics, the Douleur Neuropathique en 4 (DN4) and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) questionnaires, were performed on 43 subjects with FBSS. Subjects underwent physical or neurosensory exam components of the DN4 and LANSS in the region of most severe pain (e.g., axial low back or lower extremities). DN4 and LANSS scores were correlated with clinical history and neurologic exam, pain-related quality of life questionnaires, and compared to an independent assessment of pain distribution. The presence of neuropathic characteristics, determined by the DN4 (62% sensitivity, 44% specificity), LANSS (38% sensitivity, 75% specificity; cut-offs of 4 and 12, respectively), or their combination (20% sensitivity, 58% specificity) was associated with higher pain intensity as measured by the visual analog scale (DN4 > 4, P = 0.001; LANSS ≥ 12, P = 0.042), modified Brief Pain Inventory-Short Form (DN4 > 4, P = 0.001; LANSS ≥ 12, P = 0.082), and Neuropathic Pain Symptom Inventory (DN4 > 4, P = 0.001; LANSS ≥ 12, P = 0.001), and greater pain-related functional impairment as measured by the Roland-Morris Disability Questionnaire (DN4 > 4, P = 0.006; LANSS ≥ 12, P = 0.018). The percentage of subjects characterized as neuropathic by the DN4 and LANSS lacked concordance (67.4 vs. 25.6), and the distribution of most severe symptoms (i.e., axial vs radicular) did not correlate with subjects determined to have neuropathic pain. Unlike other neuropathic syndromes, the neuropathic component of FBSS is less reliably identified by the LANSS and DN4.