Supplementary Material for: Development and Validation of a Self-Administered Questionnaire for Myasthenia Gravis Patients

Background: To date, the investigation of the epidemiological profile of myasthenia gravis (MG) is sparse, and the influence of environmental and lifestyle factors on the occurrence of the disease remains thus unknown. The main aim of this study, which is part of a European collaborative project (EuroMyasthenia), was to develop a self-administered questionnaire to investigate these potential predisposing factors for MG. No instrument for investigating these particular factors has previously been designed for MG patients. Material and Methods: The questionnaire was developed in 3 stages: (1) devising a draft questionnaire based on questions derived from previously validated questionnaires and self-designed questions on MG characteristics; (2) testing the questionnaire on Norwegian MG patients (n = 57), and (3) assessing the content and criterion validity, and test-retest reliability, of the final questionnaire. Results: The questionnaire was easy to use and showed good feasibility for MG patients. Psychometric evaluation established the validity and reliability of the self-designed questions on MG characteristics. Conclusion: This is the first validated instrument developed to identify self-assessed environmental factors and potential predisposing factors for MG, and suitable for use in large-scale epidemiological studies.