The Extent of Cognitive Impairment in Multiple Sclerosis
In his original characterisation of multiple sclerosis (MS), Jean Martin Charcot noted a loss of memory and reduced understanding,1 but this wisdom was overlooked for a century. It is only since the early 1980s that cognitive impairment in MS has begun to be scientifically investigated and understood.2
In part this may be because reduced functioning in the context of complex physical disability may seem reasonably attributable to physical impairments. In addition, the typical pattern of cognitive deficits in MS, with intact language masking inefficiencies in concentration, memory and reasoning, may escape casual (or even clinical) observation.
The prevalence of cognitive impairment in large heterogeneous groups of MS patients has been demonstrated by formal psychometric assessment to be 43–70%, with the higher prevalence rates from clinic samples.3 Cognitive impairment has been reported at all stages and in all subtypes of the disease. In the comparative study by Potagas et al., the cognitive impairment prevalence rates were 27.3% in clinically isolated syndrome (CIS), 40.0% in relapsing–remitting MS (RRMS), 56.5% in primary progressive MS (PPMS) and 82.8% in secondary progressive MS (SPMS).4 A cognitive impairment prevalence of 45% has been demonstrated in benign MS.5 Cognitive impairment tends to progress over time, but rarely in the space of a few years.6
The Impact of Cognitive Impairment in Multiple Sclerosis
Cognitive impairment has been shown to have an adverse effect on the lives of people with MS, over and above that imposed by their physical impairments. Cognitive impairment leads to reduced employment, social function,7 physical independence, sexual function,8 progress in rehabilitation,9 everyday life activities,10 safety in driving11 and adherence to medication.12 Poorer self-reported scores on formal measures of quality of life have also been linked to cognitive status. Reduced information-processing speed has been associated with lower quality of life.13