Diaphragmatic ultrasound could unmask subclinical respiratory dysfunction in non-severe myasthenia gravis: a cross-sectional analysis.

While myasthenic crisis is well-characterized, subclinical respiratory muscle dysfunction in non-severe disease (MGFA Class I-III) remains under-recognized. To evaluate estimated diaphragmatic contractility using ultrasound in non-severe MG, and to determine its association with concurrent pulmonary function and generalized disease severity. 50 patients with confirmed non-severe MG (MGFA Class I-III) underwent concurrent evaluation using B-mode diaphragmatic ultrasound, spirometry and validated clinical scales (QMG, MG-ADL). Diaphragmatic thickness was measured at end-expiration (Tmin) and maximal inspiration (Tmax) at the zone of apposition. The Thickening Ratio was calculated as TR = Tmax/Tmin. While resting thickness (Tmin) was preserved, patients with abnormal spirometry exhibited significantly lower Tmax (p = 0.02) and TR (p = 0.016). TR showed a modest positive correlation with FVC % predicted (r = 0.298, p = 0.036) but did not correlate with QMG or MG-ADL. The absolute between-group TR difference was small, and its clinical significance remains uncertain. In non-severe MG, lower estimated diaphragmatic contractility (TR) is associated with abnormal spirometry, independent of generalized severity scores. We hypothesize this TR relative reduction could reflect a loss of individualized physiological respiratory reserve. However, the clinical significance of this absolute TR difference remains uncertain, strictly requiring prospective longitudinal confirmation.