Correlation of Quantitative Myasthenia Gravis and Myasthenia Gravis Activities of Daily Living scales in the MGTX study

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.