Construction and validation of a quality of life questionnaire for neuromuscular disease (INQoL)

Background: Because there is no muscle disease specific measure of quality of life (QoL), we wanted to develop and validate an individualized muscle disease specific measure of QoL for adults suitable for both clinical and research use. Methods: A literature review exploring QoL and its measurement resulted in the development of a theoretical model of QoL. This was used alongside qualitative interviews (n = 41) and a postal survey (n = 252) to design a questionnaire. The psychometric properties, validity (n = 95), reliability (n = 40), and responsiveness (n = 25) of the scale were assessed. Results: The Individualized Neuromuscular Quality of Life questionnaire (INQoL) consists of 45 questions within 10 sections. Four of these focus on the impact of key muscle disease symptoms (weakness, locking [i.e., myotonia], pain, and fatigue), five look at the impact (degree and importance of impact) muscle disease has on particular areas of life, and one section asks about the positive and negative effects of treatment. The questionnaire is structured to allow for variations in the individual characteristics that influence quality of life. Psychometric evaluation established construct validity and test-retest reliability. A preliminary assessment of responsiveness was obtained. Conclusions: The Individualized Neuromuscular Quality of Life is a validated muscle disease specific measure of quality of life developed from the experiences of patients with muscle disease and can be used for individuals or large sample