Relationship between Soleus H Reflex and Balance Metrics in People with Multiple Sclerosis

Abstract

Multiple Sclerosis (MS) is a disease of the central nervous system with poor balance as one of the most reported symptoms. Previous research has shown limb to limb differences in a number of physiological measures (e.g., leg strength). One measure yet to be evaluated between limbs in MS patients is the soleus Hoffmann (H) reflex, which is regarded as the electrical analogue to the stretch reflex. PURPOSE: The intent of this study was to 1) quantify the soleus H reflex in both legs to determine whether asymmetry was present and 2) correlate H reflex asymmetry to balance performance. METHODS: The study consisted of six visits. The first visit consisted of paperwork and familiarization. The soleus H reflex was measured twice in both legs over four visits (V2 - V5) to assess bilateral differences in 17 participants (MS=9, Age=49.3±11.3 years; Non-MS=8, Age=48.6±11.3 years). Balance testing was conducted on the final visit, and consisted of a sensory organization test (SOT) and limits of stability (LOS). RESULTS: One MS participant was unable to complete balance testing, leaving 16 participants in the balance analyses. The mean expanded disability status score for the MS participants was 3.4±2.2 (range=1 to 6; median=2), indicating mild-to-moderate disability. No difference was observed between limbs in the soleus H reflex for either group; however, when converted into an asymmetry score (AS) the MS group had significantly more asymmetry (MS=26.1±16.6, Non-MS=4.6±3.9; p=0.01). The MS group had a significantly lower SOT composite score (MS=80.4±4.0, Non-MS=85.8±2.9, p < 0.05). Sagittal plane endpoint excursion (EPE) and maximum excursion (ME) were significantly less in the MS group (EPE: MS=36.8±9.2, Non-MS=69.0±11.4, p <0.001; ME: MS=61.5±16.4, Non-MS=83.0±10.2, p <0.01) during LOS testing. A significant negative relationship was observed between AS and EPE (r=-0.625), ME (r=-0.709), and directional control (r=-0.615) during LOS testing in the sagittal plane. A significant positive relationship (r=0.518) was observed between AS and reaction time in the sagittal plane during LOS testing. CONCLUSION: Differences in the soleus H reflex asymmetry was observed between groups, which appears to significantly influence balance performance as the Non-MS participants generally performed better than the MS participants.