Expiratory muscle strength as a predictor of functional exercise capacity in generalized myasthenia gravis

OBJECTIVES: To investigate the correlations between the 6-minute walk test and disease severity, pulmonary functions, and respiratory muscle performance in patients with generalized myasthenia gravis (MG) and to determine whether MG disease severity, pulmonary functions, and respiratory muscle performance contribute to 6-minute walk test distance in generalized MG. METHODS: This cross-sectional trial was conducted at Hacettepe University in Ankara, Turkey. The study was carried out from February to August 2017. Twenty-eight class II-III MG patients participated in the study. Patients’ disease severity was determined with the Myasthenia gravis composite scale. All participants underwent the 6-minute walk test, pulmonary function tests, and respiratory muscle strength and endurance assessment. RESULTS: Approximately 40% of patients’ expiratory muscle strength were under the lower limit of normal. Multiple linear regression analysis revealed that the percentage of predicted expiratory muscle strength that patients reached were significant and independent predictor of percentage of 6-minute walk test distance that patients reached according to reference values (R2=0.493, F [1-27]=25.275, p<0.001). CONCLUSION: Expiratory muscle strength is a significant determinant of functional exercise performance in generalized MG with mild or moderate weakness affecting muscles other than the ocular muscles.