Pain is common in MS, affecting most people during their disease course, sometimes severely and often persistently. There are interesting results from research which compares pain in all people with MS in a defined geographical area, and age and sex matched controls or national data. The prevalence of pain is similar between MS and non-MS populations, but in MS, pain may be more severe and produces more impact on daily life.
A large sample of people with MS drawn from the North American Research Committee On Multiple Sclerosis (NARCOMS) Patient Registry showed that severe pain was more common in women, in those with MS-related disability and in individuals without higher education. Severe pain was perceived to interfere with many aspects of daily life, notably recreation, work and mobility.
Whether analysing an individual or a population, it can be difficult to understand the relative significance of different types of pain, to quantify pain, and to understand its impact on a person. One way to understand the impact of pain is to study health-related quality of life in people with pain.
Health-related quality of life
Quality of life is a complex concept, often difficult to define. For health-related studies, general concepts such as life satisfaction or living standards are not primarily considered. Instead researchers examine aspects of personal experience that might be related to health and health care. Domains that people consider important include pain, mobility, activities of daily living (ADL), relationships, work, dependence, body image and the future. Most published quality of life scales measure some of these but none all. However, pain is frequently included.
Measurement of health-related quality of life
Health-related quality of life measures can begeneric or disease-specific. Generic measures include areas like pain or mobility which are widely acknowledged to influence health-related quality of life. Generic measures are often familiar to a wide audience and results can be used to compare health-related quality of life between different conditions. Examples of commonly used generic health-related quality of life measures are the SF36, EuroQol and the Nottingham Health Profile. However, studying aspects of quality of life which are associated with a specific condition require a disease-specific health-related quality of life scale. For MS these include the Functional Assessment of MS (FAMS), or two scales based on the generic SF36; the MS Quality of Life health survey (MSQoL 54) which adds 18 additional items relevant to MS, or the MS Quality of Life Index (MSQoLI) which adds nine additional items.
The influence of pain on quality of life
The relationship between pain and health-related quality of life is complex and not fully understood.
Health-related quality of life examined in population-based studies, which compare all people with MS in a specified area to national statistics, report that the physical function, vitality and general health domains of people with MS are worse than the general population. Other research has shown that in MS, mental health correlated with pain, and that anxiety and depression in women were significantly related to chronic pain.
Unpublished British data suggests that people with MS with pain have less energy than those without pain. In summary, the available data suggests that in MS, health-related quality of life may be worse in terms of physical function and energy and, if chronic pain is experienced, mental health may be adversely affected.
Nevertheless these studies also show that healthrelated quality of life in MS may be relatively wellpreserved, with the majority of people satisfied with their quality of life. Researchers in quality of life have long realised that the measured quality of life of groups may be higher than healthy observers would anticipate. For example, 50 percent of a sample with moderate to severe disability experiencing ADL problems, social isolation and limited income reported at least a good quality of life, and people with peritoneal dialysis or haemodialysis showed higher quality of life than the general population. This disability paradox is explained in part by a response shift - that is, the frame of reference by which a person judges quality of life may change over time.
It is important to acknowledge the complexities of analysing the causes of pain, its relation to MS, measuring pain and relating pain to quality of life.
Apart from understanding the difficulties of measuring quality of life over time, research suggests that if quality of life is used as an outcome measure for an intervention, anxiety and depression must also be assessed as they influence the relationship between disability and quality of life.
We need to consider how pain impacts on disability and quality of life. Pain, like fatigue and mood, is not well measured in most disability scales. Therefore, assessing disability using these scales will underestimate issues like pain or fatigue that are important to people with MS. Pain may also directly influence an individual’s participation in life. This may be because physical discomfort causes social withdrawal, or because pain worsens mental health (or poor mental health worsens pain and participation). It is clear that careful studies are needed to unravel these relationships.
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