People with multiple sclerosis (MS) are at a greater risk than the general public of developing any type of dementia, with that of Alzheimer's disease being more than twice as high and vascular dementia nearly four times as high, a study from Korea suggested. This risk also was higher in MS patients than in those with neuromyelitis optica spectrum disorder (NMOSD), a related neurological disorder of the central nervous system (CNS, brain and spinal cord). While cognitive dysfunction is known in MS, it "can be modulated by disease-modifying drugs and cognitive rehabilitation," the researchers wrote. But such treatment differs from those specific so Alzheimer’s disease, so that "the coexistence of these disorders not only needs to be recognized, but it is important to distinguish them from one another." The study, “The risk of dementia in multiple sclerosis and neuromyelitis optica spectrum disorder,” was published in the journal Frontiers in Neuroscience. Slower information processing is a known cognitive challenge of MS. MS is marked by the immune system mistakenly targeting the myelin sheath, the protective coating around nerve fibers that facilitates efficient transmission of electrical signals. Damage to myelin disrupts nerve cell communication, leading to a wide range of disease symptoms, including cognitive impairment. Cognitive problems in MS generally concern slower information processing speeds and the emergence of new learning disabilities. They are estimated to affect around 30% to 70% of adult patients, "depending on study population and definition of cognitive impairment," the researches noted. These problems are more prominent in people who have advanced to secondary progressive MS from the disease's initial relapse-remitting MS form. As patients age, other types of dementia can overlap with MS-specific cognitive deficits, exacerbating cognitive decline. For instance, problems with verbal fluency, which is not a typical MS-associated symptom, have been observed in patients with an average age of 62, the researchers wrote. “However, knowledge regarding the association between CNS demyelinating diseases and dementia of other pathologies, such as [Alzheimer’s disease] or vascular dementia, is limited,” they noted. Information from the Korean National Health Insurance Service database, spanning January 2010 to December 2017, was used to assess the likelihood of dementia in people with MS and with NMOSD, a demyelinating disease that primarily affects the optic nerve, which transmits signals to and from the eye, and the spinal cord. These data covered 1,347 MS patients and 1,460 NMOSD patients, 40 years or older, who had not been diagnosed with dementia over the previous year. Healthy adults, serving as controls, were matched for each group based on age, sex, and the presence of comorbid diseases, including diabetes, hypertension (high blood pressure) and dyslipidemia (abnormal level of fats in the blood), as these have been associated with dementia in previous studies. Risk of any type of dementia with MS 2.34 times higher than for healthy adults. Among MS patients, most were women (58.1%), and about one-fifth (20.8%) were older than age 65. The group's mean age was 56.2, and 43.9% had high blood pressure, 31.3% had dyslipidemia, and 16.9% had diabetes mellitus (type 2 diabetes). During a mean 4.4 years of follow-up, the incidence of any dementia among these MS patients was 17.08 per 1,000 person-years compared with 7.36 for controls. This corresponded to a 2.34 times higher risk of developing dementia. (Person-years is a composite measure; here it reflects the number of events that happen in a group of 1,000 individuals within the span of one year.) Based on similar calculations, the risk of people with MS developing Alzheimer’s disease was 2.23 times higher than for controls, and that of vascular dementia — changes in memory, thinking, and behavior resulting from conditions affecting blood vessels in the brain — was 3.75 times higher. For NMOSD patients, the risk of developing any dementia was 2.19 times higher than for healthy controls, with an incidence of 9.04 per 1,000 person-years compared with 4.56 (controls). These patients were also at a higher risk of developing Alzheimer’s disease (1.99 times higher than controls) and vascular dementia (3.21 times higher). Compared with MS patients, however, NMOSD patients were 33% less likely of having any dementia and 38% less likely of having Alzheimer’s. Vascular dementia risk was similar between the two groups. A patient's age also affected relative risk. The likelihood of any dementia, including Alzheimer’s, was more pronounced among MS or NMOSD patients ages 40 to 64 than those older than 65. Dementia due to Alzheimer's may affect MS patients of younger ages. While Alzheimer's is generally associated with advanced age, "our results may suggest that in younger patients, where the effect of age on [Alzheimer's disease] risk is small, MS or NMOSD contributes to the increased risk of [Alzheimer's] much more than in older patients," the researchers wrote. Across both patient groups, those without high blood pressure also were at a higher risk of developing any dementia or Alzheimer’s disease than were those with high blood pressure. "The risk of dementia was higher in MS and NMOSD patients than in the general population and the dementia risk in MS patients was higher than in NMOSD subjects," the researchers concluded. One possible reason is the "ongoing neurodegeneration" that marks an advance to secondary progressive MS, while secondary progression is unlikely in NMOSD. "Clinicians should be vigilant regarding cognitive impairment in patients with MS and NMOSD," they added, as the potential causes of dementia can be beyond those of MS or NMOSD itself, and prevention and treatment strategies differ according to the underlying disease. Further study is needed into the mechanisms behind dementia, particularly Alzheimer's and vascular dementia, in people with MS and NMOSD, the researchers wrote.