Validity and reliability of two muscle strength scores commonly used as endpoints in assessing treatment of myasthenia gravis

Valid and reliable measurements of muscle impairment are needed to assess t herapeutic efficacy in patients with generalized myasthenia gravis (MG). In 22 patients we compared the validity and interobserver reliability of two scoring methods commonly used as main endpoints in clinical trials, i.e., t he Myasthenic Muscle Score (MMS) ranging from 0 to 100 (normal) and the Qua ntified Myasthenia Gravis Strength Score (QMGSS) ranging from 0 (normal) to 39. Each score is correlated more with functional scale and less with the patient's self-evaluation. Using intraclass correlation we found strong agr eement between observers for both the MMS (r = 0.906) and the QMGSS (r = 0. 905). The correlation between MMS and QGMSS was high (r = 0.87). The reliab ility of neither score depended on any specific item, since the removal of individual items did not significantly alter the intraclass correlation coe fficient (ranging from 0.86 to 0.93).