Introduction: Accurate measurement of myasthenia gravis (MG) severity is required for appropriate clinical monitoring of patients with MG and assessment of the benefit of new treatments in clinical trials. Our objective was to explore how MG severity can be measured and to determine how the newly developed MG Symptoms Patient-Reported Outcome (PRO) instrument complements the available measures of MG severity.
Methods: The conceptual coverage of the Quantitative MG (QMG), MG Composite (MGC), MG-Activities of Daily Living (MG-ADL), and MG Symptoms PRO was scrutinized against core symptoms of MG: muscle weakness in three muscle groups (ocular, bulbar, and respiratory), muscle weakness fatigability, and physical fatigue. Post hoc analyses of the MG0002 study, a Phase 2a clinical trial of rozanolixizumab in adults with moderate to severe generalized MG, included correlation and Rasch model analyses.
Results: The qualitative appraisal highlighted that only the MG Symptoms PRO captured physical fatigue. Data from 541 assessments (43 unique patients) were used for the analyses. Correlations ranged between 0.56 and 0.74 for the MG-ADL, QMG, MGC, and MG Symptoms PRO Muscle Weakness Fatigability score, and between 0.20 and 0.71 for the MG Symptoms PRO scores focusing on independent muscle groups. Analyses with the Rasch model estimated a meaningful continuum of severity of MG, including all items, except ocular muscles, from the four instruments. The QMG and MG Symptoms PRO had the broadest coverage of the MG severity continuum. Muscle fatigability and physical fatigue were more characteristic of low severity while bulbar weakness indicated more severe MG.
Conclusion: The severity of MG can be reflected in a meaningful continuum underpinned by the MG-specific outcome measures. Only ocular muscle manifestations were shown to reflect a possibly different facet of MG severity. With its modular nature and comprehensive content, the MG Symptoms PRO provides complementary information to the outcome measures widely used in MG.
Trial registration: ClinicalTrials.gov identifier: NCT03052751.
Keywords: Clinician-reported outcomes; Myasthenia gravis; Outcome measure; Patient-reported outcomes; Symptoms.
Myasthenia gravis (MG) is a chronic disease affecting the communication between nerves and muscles. People with MG experience muscle weakness that worsens after activity and improves after rest. MG can affect different groups of body muscles (e.g., around the eyes, in the limbs, and face or throat).We show that the various symptoms of MG can be used to summarize the overall severity of the disease: people with mild and moderate MG often report only the fast onset of weakness in their limb muscles and mild physical fatigue, while those with more severe MG report more severe fatigue and also difficulties associated with weakness in facial and throat muscles (leading to difficulty with swallowing or speaking) and in respiratory muscles (making breathing difficult). This ordering of MG manifestations will help create more accurate methods to assess the severity of MG that can be used to evaluate new treatments or to monitor patients in the clinic.We also suggest that weakness of muscles around the eyes (leading to eyelid drooping or double vision) may represent a unique aspect of MG, and may not provide as much information to summarize the severity of MG as other symptoms. However, this needs further investigation as our study did not include participants who had weakness in eye muscles as their only symptom.We also document the ability of the MG Symptoms Patient-Reported Outcome questionnaire, a new questionnaire completed by patients, to provide useful information for measuring the severity of MG.
© 2023. The Author(s).