Structural and dynamic characteristics in sonographic evaluation of the sciatic nerve in patients with probable neuropathic pain - A cross-sectional study.

Introduction: Structural and dynamic alterations of peripheral nerves are commonly observed in patients with radiculopathy. The current study aimed to compare the cross-sectional area (CSA), echogenicity index (ECHO), and skin-to-nerve distance (SKN) of the sciatic nerve between the symptomatic and asymptomatic sides of patients with probable neuropathic pain under different levels of nerve tension.

Methods: A cross-sectional study was conducted with 31 participants classified as having probable chronic neuropathic pain. The CSA, ECHO, and SKN of the sciatic nerve of both lower limbs were measured in the following positions: A) flexed knee and neutral ankle, B) extended knee and ankle plantarflexion, and C) extended knee and ankle dorsiflexion. Sonographic measurements of both lower limbs were compared using repeated measures analysis of variance.

Results: The mean age of the sample was 44 years (SD 10; 77.4% females), and the mean pain intensity was 5.3 (SD 1.9) out of 10 on the Numeric Pain Rating Scale. No significant differences were found for CSA, ECHO, or SKN measurements between the symptomatic and asymptomatic sides for the three tested positions. Position C had a smaller CSA of the sciatic nerve on both sides compared to position A. Both sides exhibited the nerve being more superficial in position C compared to the other positions.

Conclusion: Participants with probable chronic neuropathic pain had similar CSA, ECHO, and SKN of the sciatic nerve between the symptomatic and asymptomatic lower limbs. Increasing sciatic nerve tension (position C) reduced CSA and caused superficial nerve displacement on both sides.