Just under half of people with MS say that they experience significant cognitive difficulties. When their cognition is formally assessed on psychometric tests in group studies, approximately half will have some demonstrable inefficiency. When the people with MS are recruited from the community, slightly less than half will show this effect on tests. When the people with MS are recruited from a university clinic, slightly more than half will have a demonstrable inefficiency. Test scores do not relate to how people manage in everyday life in a simple way. This is partly because of external factors influencing test performance (see contributory factors).
The types of tasks that are most likely to be affected in MS are those requiring complex attention (for example, difficult arithmetic problems done without paper and pencil) and memory for information that has just been heard or seen (e.g. remembering a list of words). Increasingly, research is pointing towards an underlying slowing in mental processing that explains all other cognitive difficulties.
Change in cognitive abilities over time is often slow or non-existent. In very long studies, which collect information over 10 years or more, it seems that there is a gradual accumulation of cognitive difficulties over time. Such studies indicate that those individuals most at risk of acquiring cognitive difficulties are those who present with them in the earliest stages of the study.
While some studies have pointed towards different cognitive profiles for the different MS subtypes (relapsing/remitting, primary progressive, secondary progressive and benign), such differences are small and very subtle.
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There are few experimental studies of cognitive rehabilitation in MS. This means there is little scientific basis on which to design rehabilitation programmes. Cognitive rehabilitation studies tend to take one of four approaches:
- cognitive retraining through drills and exercises (often computerised);
- neuropsychology-model based interventions, which rely on theories of how the brain stores and processes information to develop and teach strategies which the person with MS can apply to different situations;
- eclectic, drawing on neuropsychology, cognitive psychology and behavioural psychology;
- holistic, addressing motivation, emotion and other psychological needs, in addition to specific cognitive skill training.
When a drug treatment is evaluated, a randomised controlled trial is carried out. Participants are randomly allocated to receive either treatment or placebo. It is relatively hard to tell a placebo tablet from a real tablet, when they have been designed to look the same. But it is much harder to devise a placebo rehabilitation programme. This means that the therapists delivering the programme and usually the participants as well, know who is receiving the “real” treatment. This can compromise the objectivity of the evaluation of the treatment.
Most rehabilitation studies rely on using neuropsychology tests of different mental skills. The scores before and after training are used to determine if positive change has occurred. Not all studies ask the participants if they found the programme useful. Very few attempt to find out if managing in daily life improved.
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