Effects of Type 2 Diabetes Mellitus and Peripheral Neuropathy on Mechanosensitivity of Lower Extremity Neurodynamic Testing
Background: Type 2 Diabetes Mellitus (T2DM) and diabetic symmetrical polyneuropathy (DSP) impact multiple types of sensation including light touch, temperature, position sense and vibration perception. No study to date has examined the mechanosensitivity of peripheral nerves during limb movement in this population. Objective: The objective was to determine the unique effects T2DM and DSP have on nerve mechanosensitivity in the lower extremity. Design: This cross-sectional study included 43 people with T2DM and 20 age-matched controls without diabetes. Methods: Straight leg raise neurodynamic tests were performed with ankle plantar flexion (PF/SLR) and dorsiflexion (DF/SLR). Hip flexion range of motion (ROM), lower extremity muscle activity and symptoms were measured at rest, first onset of symptoms (P1) and maximally tolerated symptoms (P2). Results: The reduction in hip flexion ROM that ankle dorsiflexion induced at P2 was approximately 50% smaller in the T2DM group compared to the control group. Individuals in the T2DM group with signs of severe DSP had no difference in hip flexion ROM between PF/SLR and DF/SLR at P1 or P2. DF/SLR did not trigger the same global increase in protective muscle guarding and did not increase symptom intensity by the same magnitude in the T2DM group compared to the control group. Limitations: This study did not assess the effects of sex on neurodynamic assessments. Conclusions: These findings support the hypothesis that increased neural loading during DF/SLR induces protective muscle guarding, reduced hip flexion motion and increased symptom intensity in healthy individuals. The SLR to the onset of symptoms is a valid assessment tool that allows for structural differentiation and is an appropriate end point for lower extremity neurodynamic testing in healthy individuals. Our study findings call into question the appropriateness of performing SLR neurodynamic testing in people with T2DM and signs of severe DSP. Without the ability to respond to the increased neural loading associated with neurodynamic testing, this population is at potential risk for harm and the information gathered will be of questionable clinical value.