Objective:

To determine the prevalence and average impact of symptoms and symptomatic themes experienced by adults with myasthenia gravis (MG) and to use this information to develop a regulatory-grade outcome measure for this population.

Background:

In preparation for future clinical trials, it is essential to understand which symptoms affect the disease burden of individuals with MG and to develop a valid outcome measure to monitor these symptoms. 

Design/Methods:

We conducted semi-structured qualitative interviews with individuals with MG to identify the potential symptoms of importance pertaining to their disease burden. We then performed a national cross-sectional study of MG patients to determine the prevalence and relative importance of symptoms identified during the initial qualitative interviews. Symptom questions and symptomatic themes were then selected for the first version of the Myasthenia Gravis-Health Index (MG-HI) based upon their prevalence and importance to the patient population, their generalizability, and their likely ability to respond to therapeutic intervention. Factor analysis was utilized to group symptom questions into subscales of MG health. 

Results:

Fifteen individuals with MG participated in the initial qualitative interviews and provided 1,872 quotes regarding the symptomatic burden of MG. Two-hundred and twenty-two participants completed a cross-sectional survey to determine the prevalence and relative importance of the most relevant symptoms identified through interviews. The first version of the MG-HI was generated and is composed of 14 subscales with optimal internal consistency and relevance to patients. 

Conclusions:

The MG-HI has extensive content and construct validity and is a viable tool to measure disease burden during longitudinal studies. Ongoing work will evaluate the usability, reliability, and known groups validity of the MG-HI in preparation for use in future studies.