Cognitive domains which were observed to be affected in our patients were attention, memory, language, visuospatial, information-processing speed, and executive functions. This proposed that MS can affect both cortical and subcortical cognitive functions. This was in agreement with numerous previous studies which described cognitive dysfunction in people with MS [12,13,14,15]. MS-related cognitive dysfunction results from domain-specific disconnection phenomena. Reduced functional connectivity between cortico-cortical and cortico-subcortical cognitive processing regions results in impairment to specific cognitive domains [16]. Cortical lesions may also responsible for cognitive deficits in people with MS [17].
Intelligence and education are responsible for the formation of cognitive reserve level which can affect the brain’s resilience in the presence of insult [18]. In the current study, people with MS who have higher levels of education showed significant better performance in only ACE language and information-processing speed compared to those having lower educational level. This was in accordance with Benedict and his colleagues who found that MS patients with a low cognitive reserve at baseline suffered a noteworthy cognitive decline [5]. However, Russo and colleagues [19] found no significant differences in the educational level between patients whose cognition was unimpaired, mildly impaired, and severely impaired.
The current work revealed that people with MS who had high EDSS showed more impairment in attention, memory, language, fluency, information-processing speed, and to a lesser extent task switching for executive functions. Amato and colleagues found that MS patients with cognitive dysfunction had higher EDSS score than those without. Also, they found that EDSS score correlate weakly with impaired cognitive functions. Moreover, they revealed that cognitive functions correlates with physical disability and may predict disability levels [20].
People with MS who experienced frequent relapses had significant impairment in attention, memory, and language. Duration of illness also affected the cognitive performance especially in memory and language as concluded in this work.
The current study showed that MS course has a significant impact on cognitive abilities. People with SPMS experienced significant worse performance in tasks of attention, memory, language, information-processing speed, and executive functions compared to those with RRMS. This agreed with Borghi and colleagues, who concluded that people with progressive MS showed a marked cognitive deficit as compared to those with RRMS and healthy controls [21].
Type of first attack may correlate to cognitive functions in MS. In this study, patients with cerebellar followed by sensory attacks showed the worst performance in attention tasks compared to patients with motor and visual attacks. Patients with cerebellar followed by motor attacks showed the worst performance in language tasks compared to patients with visual and sensory attacks; these findings may direct attention to the role of cerebellum in cognition.
Treatment type may contribute to impairment of cognitive functions in people with MS. We found that attention, memory, language, and information-processing speed were significantly better in patients receiving immunomodulatory drugs compared to those on immunosuppressive medications. This agreed with Fischer and colleagues, who reported that interferon Beta 1a had a significant favorable effect on attention, memory, visuospatial abilities, information processing, and problem solving [22]. Available immune-modulatory treatments for multiple sclerosis rapidly inhibit the inflammation and reduce the progression of brain atrophy, and they may also have neuro-protective properties [6].