Neuromuscular diseases (NMDs) encompass many diseases which impair muscle function, either directly through pathologies of the muscles, or indirectly through pathologies of the nerves or neuromuscular junctions. NMDs are progressive diseases which can cause muscle weakness or spasticity, and increased and increasing need for supportive devices and medical and non-medical support. We developed two self-report instruments to measure disability in NMDs and examined the consequences of NMDs on functioning and quality of life. We also examined the prevalence and severity of stigmatization among NMD patients and the impact on quality of life.

In the introduction in Chapter 1, we described the central concepts in this thesis: the pathophysiology and epidemiology of the broad and extensive group of NMDs, and the consequences of NMDs on physical, mental and social functioning. We then introduced the International Classification of Functioning, Disability and Health (ICF) as a suitable classification method for the development of a measurement instrument for the assessment of disease-related functioning and disability. Stigmatization was introduced as a relevant consequence of physical, mental and social disabilities in NMDs. We then described the broad concept of quality of life (QoL) and what is known about the impact of having an NMD on QoL. Finally, we described the characteristics and importance of patient reported outcome measurements (PROMs) and how to examine their psychometric properties.
We concluded with the following research questions:
1 What is the content validity of the initial ICF Core Set for NMDs?
2 How should the prevalence and severity of NMD-related disabilities, using the ICF Core Set for NMDs, be assessed?
3 What is the impact of a broad range of NMD-related disabilities on QoL?
4 How should disability severity be assessed when focusing on extremity functioning in patients with an NMD?
5 What is the impact of stigma on the QoL of patients with an NMD?

In Chapter 2 we described the validation of the initial ICF Core Set for NMDs. This initial Core Set was originally developed for three neurological diagnoses: Multiple Sclerosis, Parkinson’s disease and Neuromuscular diseases. To examine the content validity of this initial ICF Core Set for NMDs, concepts in established and validated NMD quality of life measurement instruments were used. Concepts were linked to relevant ICF categories. Next these categories were compared with the ICF categories in the initial Core Set. The final NMD-ICF Core Set reflects a broad scope of NMD-related problems in functioning. In Chapter 3 we described the development of the Neuromuscular Disease Impact Profile (NMDIP). The first step was to develop an initial questionnaire based on the NMD-ICF Core Set. The second step was to carry out a cross-sectional postal survey on NMD patients. We then constructed robust scales and examined the psychometric properties of these scales. The final NMDIP consists of 36 items divided into eight scales with satisfactory psychometric properties, and four single items. In Chapter 4 we examined the stability over time and the Relative Validity of the NMDIP scales. The NMDIP is sensitive to detecting clinically important differences between relevant subgroups, and performed as well as or better than the concurrent measurement instruments.
In Chapter 5 we reported on the prevalence and severity of a broad range of NMD-related disabilities and the impact of these disabilities on QoL. We found no differences in QoL between diagnosis-based subgroups. ‘Impairments in muscle functions’ had the highest prevalence and severity scores in the overall sample and diagnosis-based subgroups, while ‘impairments in mental functions and pain’ was the most important predictor of QoL, followed by ‘restrictions in participation in life situations’. In Chapter 6 we described the adaptation and combination of two self-report measurement instruments for the assessment of disability-severity in NMD patients and examined the psychometric properties of this measurement instrument. The Extremity Functioning Index (EFI) proved to be a sound and easy to apply self-report disability-severity measurement instrument that was able to detect clinically important differences between relevant disability-severity subgroups.
In Chapter 7 we reported on the influence of stigma on the QoL of patients with an NMD. We performed a postal survey among NMD patients and found that most patients (86%) reported self-stigma, while 64% reported enacted stigma. Self-stigma was a stronger predictor of poorer QoL compared with enacted stigma. In other words, patients suffered more from shame and fear of discrimination (self-stigma) than from actually experienced discrimination and exclusion (enacted stigma).
In Chapter 8 we summarized and reflecte