Background Progressive MS is associated with a high frequency of cognitive impairment.¹ However, it is not clear to what extent this reflects global dysfunction, or independent deficits in specific functions.Reduced speed of information processing, together with impairment in executive functions, recall–memory, and attention are the most frequently described deficits, particularly in the most extensively studied patient group with relapsing–remitting disease.² However, language and visuospatial functions have rarely been evaluated, despite evidence of involvement in large cohort studies,³ as well as in studies specifically assessing these domains.⁴ It therefore remains unclear whether cognitive dysfunction in MS reflects a universal deficit of all functions, or whether impairment of specific functions occurs independently.

Objective To characterise patterns of cognitive impairment in progressive MS on a multi–dimensional cognitive assessment tool well established in neurodegenerative diseases.

Methods Patients with secondary (SPMS; n=60) and primary progressive MS (PPMS; n=28) were assessed using the Addenbrooke's Cognitive Examination–Revised (ACE–R) multi–dimensional cognitive assessment scale. Independent dimensions of impairment and their relative contribution to the overall burden of cognitive dysfunction were then determined by hierarchical factor analysis.

Results Two independent dimensions of impairment were seen: frontal–executive (attention, verbal fluency, recall) on one hand, and language and visuospatial functions on the other. These accounted for 55% and 45% respectively of the variance not explained by a global influence (14.2% and 11.6% respectively of total variance). Isolated language and visuospatial dysfunction was seen in both groups, whereas isolated impairment in frontal–executive functions was underrepresented in SPMS (p=0.001) and not seen in PPMS patients (p=0.040).

Conclusions In addition to a prominent global influence on cognitive performance, patients with progressive MS commonly exhibit independent language and visuospatial deficits. Evaluation of these abilities should therefore be included in clinical assessment of cognition in progressive MS. The underrepresentation of frontal–executive dysfunction also seen in our study raises the possibility that language and visuospatial deficits may be characteristic of cognitive impairment in progressive MS.