Multicenter Validation Study of the Evergreen Myometric Strength Test for Lower Extremities (EMST-LE) in Multiple Sclerosis

Background: Quantitative measurement of leg strength may improve the accuracy and sensitivity of strength examination for both clinical and research purposes in MS.

Objectives: This was a multicenter validation of the Evergreen Myometric Strength Test of lower extremities (EMST-LE) using a hand-held dynamometer (HHD) with comparison to manual muscle testing (MMT).

Methods: We tested 27 people over 3 EDSS categories, Group 1) 0-3.5, Group 2) 4.0-5.5, Group 3) 6.0-7.5. Subjects were tested using standardized protocols for HHD and MMT by two trained physical therapists in random order at two visits (4 tests per subject). Testing occurred at three sites: a community hospital, a university hospital and a Veterans Affairs Medical Center. Four bilateral muscle groups [hip flexors (HF), knee extensors (KE), knee flexors (KF), and ankle dorsiflexors (AD)] were tested. A lower extremity strength sum score (LE-SSS) was calculated by summing the HHD measurement for each muscle group. Intra-class correlation coefficients (ICC) were used to assess inter-rater and intra-rater agreement.

Results: Strength testing took on average 10 minutes for HHD and 4 minutes for MMT. Both types of testing were well-tolerated. Group 1 had the highest strength measurements for all muscle groups (HHD and MMT) and for the HHD-derived LE-SSS, there was a linear decline across the three EDSS categories (Group 1 = 152.3kg, Group 2 = 121.7kg, Group 3 = 78.2kg). Inter-rater reliability was higher for HF and KF than for KE and AD by both HHD and MMT methods. Whether testing by HHD or MMT, inter-rater reliability was high at Sites 1 and 2, but poor at Site 3. For the LE-SSS, ICC were the following: Inter-rater: 0.93 (Site 1); 0.86 (Site 2); 0.24 (Site 3); Intra-rater: 0.97 (Site 1); 0.93 (Site 2); 0.83 (Site 3). Inter-rater ICC were generally lower for Group 1 than for Groups 2 and 3.

Conclusions: The EMST-LE provides a quantitative composite measure (LE-SSS) of lower limb strength that may be used for EDSS levels up to 7.5. With this method, inter-rater reliability was higher for patients with higher rather than lower EDSS, suggesting that strong subjects could overwhelm the resistance of some examiners. This method had high intra-rater reliability, but low inter-rater reliability at one site where there was a change of one evaluator during the study. This suggests the importance of training and consistent personnel for test reliability.