Introduction: Quantitative Myasthenia Gravis (QMG) and Myasthenia Gravis Activities of Daily Living (MG-ADL) scales were compared using the data from the Thymectomy Trial in Non-Thymomatous Myasthenia Gravis Patients Receiving Prednisone Therapy (MGTX) study.
Methods: Correlation between QMG and MG-ADL raw and change-from-baseline scores was calculated every 3 months for 60 months based on treatment groups and minimal manifestation status (MMS).
Results: QMG and MG-ADL change-from-baseline scores correlated significantly, with increasing strength of correlation over time, in both treatment groups. QMG and MG-ADL raw scores correlated significantly in both treatment groups, with increasing correlation only in the prednisone-alone group. Correlation between raw scores was weaker in patients who were in MMS, demonstrating a "floor effect" on the MG-ADL scale. Raw QMG scores could be modeled assuming a normal distribution, whereas raw MG-ADL scores could not be modeled this way.
Discussion: The floor effect and skewed distribution of the MG-ADL measure should be taken into account in the design of myasthenia gravis clinical trials.
Keywords: MG-ADL; MGTX; QMG; myasthenia gravis; outcome measure; trial design.
© 2020 The Authors. Muscle & Nerve published by Wiley Periodicals, Inc.