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Abstract
The aim of the current study was to assess the relation between working memory dysfunction and clinical and MRI findings in relapsing remitting multiple sclerosis. This study was conducted on fifty patients with clinically definite relapsing remitting multiple sclerosis, they were recruited from the out patient clinic of Alexandria university hospitals; and twenty-five healthy controls matched for age, sex, and educational level, they were selected from general population through personal communication.
All subjects (patients and healthy controls) were subjected to complete medical history, thorough physical, neurological and psychiatric examination, and routine laboratory investigations. Neuropsychological assessment was done including: Digit span, Visual span, N-Back task and Wisconsin card sorting test. The patients group were further subjected to: Expanded disability status scale (EDSS) and brain MRI.
As regarding working memory, this study suggests the following practical model : working memory is not a unitary process, but it is formed from four subcomponents, which are controlling attention, retentive subcomponent, updating subcomponent, and executive subcomponent.
Results of this study were as follow:
This study suggests that according to the resources utilized by cognitive tasks, working memory tasks my be classified into high demanding working memory tasks (2-back task and WCST) and low demanding working memory tasks (1-back task and digit and visual span), and in relapsing remitting multiple sclerosis working memory dysfunction includes mainly high demanding working memory tasks.
Clinically, the present study found no statistically significant correlations between working memory dysfunction and age, age at onset, gender, number of relapses, affected functional system, or EDSS status. Alternatively, there were statistically significant positive correlations between working memory dysfunction and the duration of illness.
Radiologically, the current study found no statistically significant correlations between working memory dysfunction and specific sites of lesions, but we found statistically significant positive correlations between number of the lesions and working memory dysfunction. The current study suggests disconnection as a potential mechanism for working memory dysfunction in relapsing remitting multiple sclerosis.
Based on the results of this study, the following recommendations are yielded:
1. Absence of correlations between the physical disabilities and working memory dysfunction in patients with RRMS infers that the latter cannot be ascertained from a neurological examination. Hence the value of neuropsychological assessment.
2. Positive correlations between working dysfunction and the duration of illness suggest that neurologist should consider periodic screening and/or assessment for working memory deficits in MS as such deficits may not be always be apparent or reported.
3. Future studies aiming at elucidating the pathophysiology of working memory dysfunction in different forms of MS should employ sensitive tests battery covering the low demanding and high demanding working memory tasks .
4. The evidence that normal-appearing white matter is far from normal remains central for understanding the mechanisms of working memory dysfunction in multiple sclerosis. Conventional MRI findings should be extended by newer imaging techniques, such as spectroscopy and diffusion tensor imaging, which are more likely to provide interesting insights about the causes of working memory dysfunction in patients with MS.
5. More research is needed to further evaluate working memory dysfunction in MS and other neuropsychiatric disorders .