Psychometric Properties of Pressure Pain Threshold Algometry for Pain in Multiple Sclerosis: An Exploratory Study

Abstract

Background and purpose: Pain is a frequent symptom of multiple sclerosis (MS). Algometry as a method to measure pressure pain threshold (PPT) has not yet been validated for test-retest reliability and construct validity in persons with MS (pwMS). This research aims to investigate the test-retest reliability and construct validity of the pressure algometry for pain in MS.

Methods: Sixty pwMS with pain were included (mean age: 51.08 ± 11.61, Expanded Disability Status Scale [IQR]: 3.75 [3.3]). The reliability (test-retest, measurement error) and construct validity (hypothesis testing) were analyzed. A digital algometer (Somedic Sales AB, Hörby, Sweden) was applied perpendicularly and bilaterally on the trapezius muscle, thumbnails, low back, and quadriceps muscle to assess local PPTs. Three trials were performed on each body site, and the mean of the trials was used for statistical analysis. To investigate test-retest reliability, participants repeated the testing at 3- to 8-day intervals.

Results: PPTs obtained by algometry showed good to excellent test-retest reliability (ICC [95% CI]: 0.82 [0.70-0.89]-0.91 [0.85-0.95]) in 4 different body parts. PPT measures had significant negative moderate correlations with pain outcome measures (the Neuropathic Pain Scale, Neuropathic Pain Symptom Inventory, Brief Pain Inventory-Short Form, Douleur Neuropathique en 4, and painDETECT) (Spearman's rho = -0.265 to -0.456) and the Modified Fatigue Impact Scale (Spearman's r = -0.281 to -0.392). Weak nonsignificant correlations were found between PPT measures and clinical variables (Spearman's r = -0.201 to 0.227).

Discussion and conclusions: PPT measurement can reliably assess pain in MS with weak to moderate validity in the neck, thumbnails, lower back, and legs.

Keywords: algometer; multiple sclerosis; pain; pressure pain threshold; reliability; validity.