Cognitive impairments in multiple sclerosis: a review

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Cognitive impairment (CI) may develop at any time during the course of the disease in the presence or absence of neurological disability. On the basis of comprehensive neuropsychological studies, there is now a consensus among investigators that 45 percent to 65 percent of MS patients suffer from some degree and form of cognitive difficulty. Features of CI include bradyphrenia; impaired attention, concentration and abstract reasoning; reduced manual speed and dexterity; deficits in memory retrieval; and language deficits in both the relapsing-remitting and progressive forms of MS. Impairments in all cognitive domains may result from the diffuse spread of microscopic pathology, although a preferential lobar distribution of plaques can present with a predominant deficit in the corresponding cognitive function. Nevertheless, the severity of CI best correlates with total microscopic and macroscopic disease burden of the brain as defined by recently developed magnetic resonance imaging (MRI) sequences. A disruption of connecting intercortical and subcortical pathways is likely to be the main cause of metabolic and functional abnormalities in neurons. However a direct toxic effect of soluble inflammatory products may also compromise neuronal function and survival. Early treatment of MS with interferons and copaxone can prevent or delay the onset of both neurological and cognitive disabilities by reducing the inflammatory activity and damage in the CNS. Until more powerful neuroprotective agents become available, simple neuropsychological screening and cognitive rehabilitation for memory and language impairments will remain important components in the care of MS patients.