Cognitive phenotypes in multiple sclerosis

Abstract

Background: Cognitive impairment is a debilitating symptom experienced by ~ 50% of multiple sclerosis patients, with processing speed (PS) and memory most affected. Until now, the field has considered cognition in a binary fashion: patients are designated as impaired or not impaired. This designation is typically arrived at by administering a full cognitive battery and assigning a cutoff (e.g., 4 of 11 tests failed) to distinguish impaired/non-impaired. This relatively coarse approach yields a heterogeneous group of "impaired" patients, some of whom may have isolated memory or PS deficits, others with combined deficits. The goal of this study is to determine whether predominant patterns of deficits, "cognitive phenotypes", can be identified in a large sample of MS patients. Proportional representation of four cognitive phenotypes will be evaluated: (1) not impaired, (2) PS-impaired only, (3) memory-impaired only, (4) PS + memory impaired.

Methods: Cognition was measured in 128 relapsing-remitting MS patients using validated tests of verbal/visual memory, and PS. Cognitive phenotype representation was evaluated. Differences in age, education, disease duration, and IQ across cognitive phenotype groups were evaluated.

Results: Four cognitive phenotype groups were represented: 56.3% not impaired, 7.8% PS-impaired, 18.8% memory-impaired, 17.2% PS + memory impaired. Across groups, there were no differences in age, education, disease duration. IQ in non-impaired was higher than PS + memory impaired.

Conclusions: Adopting a novel classification taxonomy for cognitive phenotypes will advance understanding of cognitive impairment and enable a precision medicine approach to the development of effective, targeted treatments for cognition in persons with MS.

Keywords: Cognition; Cognitive impairment; Multiple sclerosis; Neuropsychology.