Diaphragmatic ultrasonography as a predictor of respiratory muscle fatigue in myasthenia gravis

Introduction/AimsEasy fatigability, the clinical hallmark of generalized myasthenia gravis (GMG), cannot be detected in a dynamic way. The aim of this study was to assess respiratory function dynamically through diaphragmatic ultrasonography (DUS) in GMG patients.MethodsGMG patients and controls were recruited in a 1:1 ratio. DUS was performed during one quiet breath and 15 consecutive deep breaths. The diaphragm thicknesses were measured at different positions. Diaphragm thickening fraction (TFdi) and the maximal change in diaphragm thickness (Tmax) during 15 consecutive deep breaths were calculated and transformed to normality, named N-TFdi and N-Tmax, respectively. The percentages of changes in TFdi and Tmax compared with baseline were named Delta TFdi and Delta Tmax, respectively. The diagnostic parameter for respiratory muscle fatigue was chosen from Delta TFdi and Delta Tmax at different deep breath times according to their ability to distinguish GMG patients from controls and the interrater reliability of TFdi and Tmax.ResultsThirty-four GMG patients and 30 healthy controls were enrolled. N-TFdi and N-Tmax significantly changed as the number of deep breaths increased (p < .001) in GMG patients, but not in controls. Delta Tmax of the 15th deep breath (Delta Tmax15) was selected as the diagnostic parameter for respiratory muscle fatigue. There were no significant differences in percentage of predicted values of forced vital capacity and arterial partial pressure of carbon dioxide between patients with normal and abnormal Delta Tmax15.DiscussionDUS could identify diaphragm fatiguability in GMG patients, which may be more reliable and sensitive in assessment of diaphragm fatigue than conventional methods.