What is Cognitive Impairment in Multiple Sclerosis?
Cognitive impairment has been reported at all phases and all subtypes of multiple sclerosis (MS). The severity and type of cognitive impairment varies among individuals and can be observed both in early and in later stages. 
We now know that MS-related cognitive impairment can have many faces and, like other symptoms of MS, cognitive deficits are highly variable.
Prevalence studies of community and clinical samples, indicate that 45-70% of MS patients are cognitively impaired, but severe dementia is relatively uncommon. Cognitive impairment contributes significantly to patients’ disability status, but there is no direct relationship between cognitive deficits and physical disability. 
Cognition refers to all of the high-level functions carried out by the human brain. The areas which have commonly shown more deficits in MS are:
-Information processing speed
How does Cognitive Impairment affect daily life?
It is known cognitive impairment increases patient morbidity and is associated with a decrease in the participation and functioning of activities of daily living, such as driving, medical decision-making and treatment adherence, money management, and work. Cognitive impairment appears to be associated with increased rates of unemployment and lower quality of life. 
Standardized neurological examinations fail to detect emerging cognitive deficits and self-reported cognitive complaints by the patients can be confounded by other subjective symptoms (fatigue, depression). Treating the depression, anxiety and fatigue can improve the cognitive alterations 
Cognitive functions can also be affected by emotional stress, depression, sleep disturbances, menopause, aging or fatigue. Some prescription medications and drug or alcohol abuse can also disrupt cognitive performance.
How can Cognitive Impairment be detected?
Even though the capability of detecting cognitive difficulties has increased over the last years, there are many undiagnosed patients.
In patients with MS and cognitive impairment the complete etiology remains unclear, as little is still known about their relative contribution to the underlying process of cognitive impairment. There is a poor correlation between the symptoms of cognitive impairment and the conventional MRI measures of structural damage. 
A neurologist can perform briefer evaluations: the SMTD (Symbol Digit Modalities Test) test has proceeded to be valuable screening tool for MS cognitive impairment. The recent consensus of the national MS society for cognitive screening recommends that a minimum early baseline screening should be done, and it can be with the SDMT and it is especially important to repeat the same test in different reassessment to show changes. 
A neuropsychologist should do assessment of cognitive function. A formal cognitive evaluation may require several hours.
The neuropsychological assessment should also discriminate between cognitive impairment and other causes for perceived deficits, including anxiety, depression, and quality of life.
Treatment and prevention of cognitive impairment
The options to treat these cognitive symptoms are still insufficient. There is limited evidence that disease-modifying therapies are effective in treating cognitive dysfunction. In cases of relapsing-remitting multiple sclerosis drug treatments may help stabilize and possibly improve cognition if the disease is caught early enough.
However, there are certain medications for MS that would help prevent cognitive decline as they have been shown to slow the progression of brain atrophy, which is a predictor of cognitive disability.
Neuropsychological rehabilitation is currently the mainstay for treatment of cognitive impairment in MS.
There is evidence that cognitive rehabilitation programs are efficacious in treating MS-related cognitive dysfunction.  Cognitive rehabilitation therapy is mental training that helps keep cognitive abilities sharp. Training that improves cognitive function can significantly improve the quality of life of a person with MS.
We should also promote primary prevention of cognitive decline, in part through interventions and healthy lifestyles that promote brain maintenance.
Identifying modifiable risk factors for development of cognitive impairment in early MS is important in order to prevent or slow decline. Smoking is a risk factor for worse cognition and physical outcomes; and co-existent excessive alcohol consumption accentuates these smoking effects. 
Physical exercise may delay the onset of cognitive problems in MS, this may be mediated through its anti-inflammatory immune effects.  There has been increasing interest in the potential of physical exercise to improve cognitive function both in healthy people and individuals with chronic conditions such as multiple sclerosis.
It is essential to include an early screening that detects impaired cognition in patients with MS; this could allow for an earlier intervention, which would include a specific work with patients and their families 
- Oreja-Guevara C, Ayuso Blanco T, Brieva Ruiz L, Hernández Pérez MA, Meca-Lallana V, Ramió-Torrentà L. Cognitive dysfunctions and assessments in Multiple Sclerosis. Front Neurol 2019 Jun 4; 10:581. doi: 10.3389/fneur.2019.00581. eCollection 2019.
- P Hämäläinen, E Rosti-Otajärvi. Cognitive impairment in MS: rehabilitation approaches. Acta Neurol Sacand. 2016 Sep;134 Suppl 200:8-13. doi: 10.1111/ane.12650
- M H Chen, N D Chiaravalloti, J DeLuca. Neurological update: cognitive rehabilitation in multiple sclerosis. J Neurol. 2021 Dec; 268(12):4908-4914. doi: 10.1007/s00415-021-10618-2
- N McNicholas, K O´Connell, S M Yap, R P Killeen, M Hutchinson, C McGuigan. Cognitive dysfunction in early multiple sclerosis: a review. QJM: An International Journal of Medicine, Volume 111, Issue 6, June 2018, pages 359-364, https://doi.org/10.1093/qjmed/hcx070