Reliability of the six-minute walk test in patients with generalized myasthenia gravis

Abstract

The purpose of this study was to assess the reliability of the six minutes walking test (6MWT) as a functional capacity test for patients with generalized myasthenia gravis (MG). Eleven patients with generalized MG (5 men, six women), aged 55±9 years, were first assessed as to pulmonary function and then submitted to three 6MWT in different days. Heart rate and oxygen saturation were measured (by means of portable oxymeter) during, and dyspnea (by the Borg scale) and distance walked were measured after, each test. At the three tests distances walked were 498 m, 517 m and 520 m (respectively 99%, 103%, and 104% of predicted values). Mean heart rate, oxygen saturation, and dyspnea values showed constant behaviour through the three tests. A high relative reliability was found between the tests, with interclass coefficient correlation over 0.90 (6MWT1-6MWT2, 0.960; 6MWT1-6MWT3, 0.945; and 6MWT2-6MWT3, 0.970); absolute reliability of 4%, 3.5% and 4.8%, as well as good repeatability of 11%, 9.8% and 13.4% were found for respectively the first, second, and third tests. Upper and lower agreement limits, as well as bias mean values by the Bland-Altman test show clinically acceptability. It may hence be said that the 6MWT proved safe, reliable and reproducible, and may be used for exercise tolerance assessment and follow up of patients with generalized myasthenia gravis.