The World Health Organization defines health as a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity. (Callahan, 1973) The International Classification of Functioning, Disability, and Health (ICF) delineates key categories of health and health-related domains, divided into two main components: Functioning and Disability and Contextual Factors. Functioning and Disability encompass Body Functions and Structures, which pertain to physiological and anatomical impairments, while Activities and Participation address an individual’s capability to perform tasks within both standard and specific environments. According to the ICF, disability arises from the interaction between symptoms, activity limitations, participation restrictions, and personal and environmental factors (World Health Organization, 2001). Health-related quality of life (HRQoL) goes beyond disability by encompassing a subjective and multifaceted view of well-being, which includes physical functioning, mental health, work status, and social relationships. Body function and structure impairments are less influenced by social and environmental conditions, making them more indicative of disease severity (World Health Organization, 2001). This is why outcome measures for disease severity typically focus on signs and symptoms, while measures of disability and HRQoL consider the broader impact on the individual. In clinical trials, aligning the primary outcome with the type of intervention is crucial. For instance, a phase II trial for a new drug would likely target changes in symptoms, while a psychosocial intervention may primarily influence HRQoL or disability rather than symptoms alone (Barnett et al., 2018).

Applying this framework to myasthenia gravis (MG) underscores the importance of assessing various health and health-related domains for a comprehensive assessment of the disease and its impact on affected individuals. Fig. 1 illustrates the interplay between these domains and how different currently used assessments relate to them. Given that muscle endurance is markedly compromised in MG, understanding the implications of this impairment on task execution within an individual’s current environment is crucial for developing robust outcome measures. This approach can guide clinicians and researchers in assessing the multidimensional impact of MG on patient functioning.

Due to the fluctuating nature of MG symptoms, disease assessment is challenging, requiring outcome tools that are both reliable and sensitive to change. To address this, the Myasthenia Gravis Foundation of America (MGFA) has encouraged the use of instruments that emphasize patient-reported outcomes (PROs) and health-related quality of life (HRQoL) (Benatar et al., 2012). While PROs primarily focus on the functional consequences of the disease, HRQoL scales are broader and encompass physical, social and psychological well-being (Burns et al., 2010a). These tools offer a more holistic view of the patient experience and are essential complements to clinician-related measures of disease activity (Barnett et al., 2018; Muppidi, 2017).

This chapter reviews validated English-language outcome measures, alongside emerging domains such as electrophysiological markers and serology, which extend beyond the traditional disability paradigm.