Cognitive performance was evaluated using the Paced Auditory Serial Addition Test (PASAT), in which a series of single digit numbers are presented and the two most recent digits must be summed. This test has high sensitivity in detecting MS-related cognitive deficits as it relies strongly on working memory and information processing speed abilities. Fatigue was evaluated through the Modified Fatigue Impact Scale (MFIS), which assesses the effects of fatigue in terms of physical, cognitive, and psychosocial functioning.
Of the 50 clinically diagnosed patients, 17 had less than 13 years of schooling, without obtaining any secondary level diploma, and 33 had received more than 13 years of schooling, leading to a diploma at university level. Both groups were administered a short neuropsychological battery including standardized tests for vigilance, alertness and divided attention. None of the tasks showed differences between the groups.
Patients were also classified using the US census categories into low occupations (student, housewife, unskilled/semiskilled, skilled trade or craft, clerical/office worker) and high occupations (manager business/government and professional/technical), where the occupational attainment categories are based on the cognitive complexity and cognitive effort needed to carry out the job efficiently. They were then further divided into three groups: low occupation and low education, low occupation and high education, and high occupation and high education.
The researchers found that high speed PASAT versions were more suitable for identifying compensatory capacities compared to low speed PASAT versions. MS patients with low education performed worse than matched healthy controls at faster PASAT speeds. By contrast, no difference was observed between MS patients with high education
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