Preliminary Analysis of Pain Phenotypes in Multiple Sclerosis on Pain Thresholds, Activity and Function

Research Objectives: Multiple Sclerosis (MS) is an autoimmune disease wherein the immune system attacks the myelin of the central nervous system, affecting approximately 1,000,000 individuals in the United States. Pain is common in people with MS (pwMS), reported as one of the most bothersome symptoms during the course of the disease. Pain exhibits considerable heterogeneity in pwMS, including nociceptive, neuropathic, nociplastic, and mixed pain. The purpose of the present study is to compare 1) pressure pain threshold (PPT) as an objective measurement of pain and 2) mobility and strength across different pain phenotypes in pwMS.

Design: A cross-sectional study

Setting: Academic Medical Center Research Laboratory

Participants: Twenty pwMS (age of 57±7.35, BMI of 29.32±8.78, and 68% women).

Interventions: N/A

Main Outcome Measures: During a single assessment session, pwMS were evaluated for pain, gait, patient determined disease steps (PDDS), level of activity, and grip strength. To determine the pain phenotype, the PainDETECT and FM-2011 questionnaires were utilized. The intensity of pain was measured subjectively using a visual analogue scale (VAS) and objectively with pressure pain threshold (PPT) measured using a digital algometer for both peripheral PPT (lower legs) and central PPT (Back of Thumbnail). Additionally, their level of physical activity was assessed using the short form of the International Physical Activity Questionnaire (short-IPAQ), spatiotemporal parameters of gait were measured with a pressure walkway, and grip strength was evaluated using a handheld dynamometer.

Results: Four participants reported no pain in the past four weeks. Sixteen pwMS experienced various types of chronic pain: nociceptive (n=6), neuropathic (n=2), nociplastic (n=4), and mixed (n=4). Individuals with mixed pain were found to have the highest average pain intensity (VAS: 5.75±0.7) and disability level (PDDS: 5±0.57) as well as the lowest (most severe) central PPT (5.3±0.8 lb/cm2), peripheral PPT at four points of the lower leg (range from 5.8±1.74 to 6.45±2.66), and the lowest grip strength (18±2.82kg). In contrast, the lowest level of physical activity was observed in the neuropathic pain group. Reduced gait speed was also observed in the neuropathic pain (63±22 cm/s) and mixed pain group (72±13 cm/s). While comparing pain versus non-painful pwMS, all variables were inferior in the painful pwMS.

Conclusions: Pain may affect mobility, function, and gait in pwMS, with mixed pain having the most considerable impact. A larger sample size study is warranted.

Author(s) Disclosures: This work was supported in part by a Mentor-based Rehabilitation Research Post-doctoral fellow grant and other funding from the National MS Society (MB-1807-31633; RG-1701-26862), and MS Run the US.