Cognitive dysfunction is a common feature of multiple sclerosis (MS) and affects approximately 40 to 60% at some point in the progression of the disease. Cognitive impairment often manifests as deficits in recent memory, attention, speed of information processing, executive functions, and visuospatial perception. Cognitive impairment is the loss of certain mental functions, such as learning, memory, perception, and problem solving. While the term tends to be associated with dementia or Alzheimer's disease, it's not always as serious or debilitating with other diseases, such as multiple sclerosis (MS).
The relationships between cognitive impairment that exist during the clinical course of multiple sclerosis (MS) remain poorly described. The effect of disease duration has been studied in a few longitudinal cohorts and in some cross-sectional studies that suggest that cognitive deficits tend to extend with the duration of the disease. However, the effect of the duration of the illness seems to be confused with the effect of age. In the preclinical stage, cognitive deficits have been observed in patients with radiologically isolated syndromes, and their profile is similar to that of clinically isolated syndromes (CIS) and relapsing-remitting MS (RRMS).
The frequency of cognitive decline tends to be higher in the RRMS than in the CIS. In these phenotypes, slow information processing speed (IPS) and episodic deficits in verbal and visuospatial memory are frequently observed, but executive functions and, in particular, verbal fluency can also be affected. More frequent and severe deficits are reported in SPMS than in RRMS, with more serious deficits in memory, working memory, and IPS tests. Similar to what is seen in SPMS, patients with primary progressive MS (PPMS) have a wide range of cognitive deficits in IPS, attention, working memory, executive functions and episodic verbal memory, with more tests and altered domains than patients with RRMS.
Taken together, these data suggest that not only the duration of the disease and age play an important role in the cognitive profile of patients, but also the phenotype itself, probably due to their specific pathological mechanism. Tests commonly used to detect cognitive deficits in dementia, such as the Mini-Mental State Examination (MMSE) or the Montreal Cognitive Assessment (MoCA), which mainly assess cortical function, are not sensitive or specific enough to assess cognition in MS, as this condition often affects other domains. Unlike the results mentioned above, in another study (which included 53 patients with RRMS with a duration of illness of one to five years and EDSS scores ≤ 5.0), general cognitive impairment was not correlated with any of the demographic, clinical, or MRI variables at the start of the study. Experiencing deficits in cognitive functioning can be alarming and annoying, but keeping up with treatments for multiple sclerosis and learning to manage problems with alternative solutions can help.
In fact, when considering the two most common cognitive processes that deteriorate in the early stage of the disease, IPS and memory, different mechanisms could be discussed. Meningeal B-cell follicles in secondary progressive multiple sclerosis are associated with the early onset of the disease and with serious cortical disease. Table 3 presents the frequency of deterioration of the different domains in the larger studies using BRB-N. Posterior lobes of the cerebellum and speed of information processing in various stages of multiple sclerosis.
The number of NP scores studied was higher than in other studies, so the criterion of two altered tests was more easily met. The cognitive profile in the RRMS is very similar to that observed in the CIS, with deficits mainly in the IPS, the deterioration of verbal and visuospatial memory and EF (studied through verbal fluency tests in previous studies). In this group of patients, the lesion burden was very small, suggesting that they were at a very early stage of the disease. One of its important components, which occurs in up to 90% of patients with multiple sclerosis, is cognitive fatigue, defined as a decrease in task performance as a result of continuous cognitive effort.
To better understand the role of the different mechanisms involved in IC, it might be worthwhile to study specific cognitive domains separately and focus on the early stages, when all the mechanisms could be more easily disentangled. In the study designed to determine the separate impact of depression and anxiety on cognition, higher depressive symptoms were associated with worse processing speed, as well as with lower employment, greater fatigue, and greater physical disability, but anxiety showed no such correlation. .
