Bilateral Sciatic Nerve Impairment in Patients with Unilateral Chronic Painful Radiculopathy: A Case-Control Study

Abstract

Introduction: Unilateral peripheral neuropathic pain is a prevalent condition, and individuals with chronic symptoms may present neural alterations beyond the symptomatic limb. Investigating both limbs in comparison with those of asymptomatic individuals may help clarify whether the sciatic nerve presents bilateral involvement. Objective: To compare the cross-sectional area (CSA) and skin-to-nerve distance (SKN) of the sciatic nerve between individuals with probable neuropathic pain and matched asymptomatic controls. Methods: A case-control study was conducted, including 31 individuals with unilateral chronic probable peripheral neuropathic pain and 31 matched asymptomatic controls. Ultrasound assessment of the sciatic nerve was performed at the posterior mid-thigh under two limb positions representing lower and higher neural tension. Group and positional comparisons were analysed using repeated-measures two-way ANOVA. Results: Individuals with neuropathic pain presented significantly greater CSA bilaterally compared with controls, with no differences between symptomatic and asymptomatic sides. In this group, CSA decreased under higher neural tension, a response not observed in controls. Skin-to-nerve distance differed between groups and positions, with controls showing greater values in both conditions. Discussion: The bilateral similarities observed within the neuropathic pain group, combined with differences relative to controls, may reflect adaptive neural changes associated with chronic neuropathic pain. Observed differences in SKN should be interpreted with caution, as they may be influenced by body composition rather than neural alterations alone. Conclusion: The findings suggest that individuals with unilateral chronic probable peripheral neuropathic pain may exhibit bilateral changes in sciatic nerve morphology when assessed by ultrasound.