2Measuring disability and quality of life in established rheumatoid arthritis
Introduction
Rheumatoid arthritis (RA) is a common autoimmune disease that has articular and extra-articular manifestations.1 It has a prevalence of approximately 0.5–1% and is most prevalent in women, with a 2.5/1 ratio between women and men.1 RA can have a major impact on health-related quality of life (HRQoL).2 The aim of this chapter is to present an overview of different instruments that are used to assess disability and HRQoL in patients with RA.
Several definitions of the word disability have been presented. In a recent review, Leonardi et al3 propose the following:
Disability is a difficulty in functioning at the body, person or societal levels, in one or more life domains, as experienced by an individual with a health condition in interaction with contextual factors.
Whereas impairment represents disturbances at the organ level caused by a pathological process; disability reflects the consequences of impairment in terms of functional performance.
HRQoL is a broad concept that can be defined as the impact of health on an individual's ability to function and on the perceived well-being in physical, mental and social domains of life.4 An important part of HRQoL is that it includes a patient's satisfaction or response to his or her health status and limitations.5, *6 The same disease state or limitation can thus affect HRQoL differently across patients, depending on personal factors.
Generic instruments are developed for use in patients regardless of disease. One of the major advantages of such instruments is the opportunity to compare results between disease groups, and so to cover a broad variety of disease-related factors. The disadvantages are that generic instruments might lack aspects that can be important in some diseases but not others; they can also be less sensitive to change.6
The disease-specific instruments described in the following sections have been developed for use in patients with RA or other arthritic diseases. Their advantage is that they aim to cover all the important factors in these conditions - exemplified by dexterity in RA – that is, components that might be less important in tools assessing a wider spectrum of diseases. The disadvantage of any disease-specific measure is that the results obtained cannot be compared with results from patient groups with other diagnoses.
Section snippets
SF-36 physical functioning
The well-known generic health profile the Short Form 36 Health Questionnaire (SF-36) contains a domain concerning physical functioning. This is based on 10 items regarding limitations in physical activities because of health problems.7 This scale can be used as a measure of physical disability. However, none of the items directly addresses dexterity, which is important in RA.
Other
Other generic health profiles (the Sickness Impact Profile, the Nottingham Health Profile) also have items that capture
Instruments measuring health-related quality of life
Two main groups of instruments measure HRQoL: profiles and utility instruments. A profile contains separate scores for several dimensions. A utility score provides only one sum score for each patient on a scale from 0.0 (a health state similar to death) and 1.0 (perfect HRQoL). Some of the instruments also allow values below 0.0, representing health states that are considered worse than death.
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