A population-based follow-up study of maximal muscle strength and mobility in patients with myasthenia gravis

It is uncertain whether residual muscle weakness in myasthenia gravis (MG) can improve, and whether it reflects deficits and disability. In a population-based follow-up study of 107 patients with MG and 50 healthy controls, maximal shoulder, knee and ankle strength was measured using isometric dynamometry and related to the quantitative MG (QMG), the MG Composite (MGC), the MG-activities of daily living (MG-ADL), the MG quality of life 15-items (QOL15) and a 400 m walk test (400MWT). During a mean follow-up of 4.6 (±0.04) years, patients improved 10.8% (P < 0.001) in isometric shoulder strength, whereas their isometric knee strength did not improve (3.2%, P = 0.151). Higher age, longer disease duration and greater baseline impairment had no negative impact. Change in isometric shoulder and knee strength did not correlate with changes in the QMG, the MG-ADL or the QOL15. Change in isometric knee strength correlated with change in the 400MWT (r = -0.357), and the 400MWT correlated with changes in the QMG (r = 0.439), the MG-ADL legs subitem (r = 0.419) and the QOL15 (r = 0.310). Overall, muscle strength improved over time, and the MG clinical scales were related to impaired mobility and muscle strength. Change in residual muscle weakness was unrelated to disability (MG-ADL) and quality of life (QOL15).