Chapter 12. Demyelinating Diseases

MS, or multiple sclerosis, sclerosis disseminata is a chronic demyelinating and neurodegenerative disease that leads to damage to myelin and nerve fibers. MS develops due to the influence of an external pathological factor (infectious or toxic) on a genetically predisposed organism. In this disease, a multi-focal involvement of the white matter of the CNS occurs. In addition, changes are observed in the visually intact white matter and in the gray matter (cortical foci). In the settings of chronic inflammatory process, which is based on autoimmune mechanisms, damage to the myelin sheaths of nerve fibers (demyelination) occurs. At the same time, focal and diffuse neurodegenerative changes develop. In most cases, MS has a steadily progressive, often cyclic (remitting) course, which in the future, as the neurodegenerative changes increase, can be replaced by a gradual progression (secondary progression). In some patients (up to 10%), MS initially has a steadily progressive course with progressing disability (primary progressive MS). In this disease, young and middle-aged patients first lose their ability to work, and in later stages, in the absence of adequate pathogenetic treatment, they lose the ability to move and self-care. Temporary disability associated with exacerbations of the disease in the early stages (remitting course), in many patients, it is subsequently accompanied by an increase in irreversible disorders and the development of persistent disability.

Epidemiology

First MS signs present more often at the age of 18 to 50 years. Currently, early onset of MS is increasingly reported in children (under 15 years of age), which is up to 10% of the total number of patients, and in people over 50 years of age.

The prevalence and incidence of MS has traditionally been higher in geographical regions farthest from the equator, especially in Northern Europe and North America. In recent years, this relation is much less pronounced, as the disease has become common in many southern regions of Europe, as well as in North Africa, Asia and Latin America. The direct relationship between the prevalence of MS and latitude is most likely due not only to the geographical location, but also to the genetic, ethnic, and medico-social factors. Nutrition, socio-economic and environmental characteristics have a significant impact on the risk of disease.

The main epidemiological characteristics of MS :

• mostly, people of the European race are affected; there are ethnic groups (Majori, Eskimos and peoples of the Far North, indigenous Indians and indigenous people of Central Africa), where MS is very rare;
• the presence of familial MS, that is, several cases of the disease;
• in blood relatives (from 3 to 10% of all cases of MS);
• in all populations, women predominate among MS patients; in recent years, the men-women ratio is 1:2, it increases to 1:3 and higher, especially in the age group from 16 to 25 years, but men are prone to an unfavorable primary progressive course of MS;
• the change in the frequency of MS among the displaced population revealed a change in the risk of MS when changing the zones of residence (migration), depending on the age of relocation (before and after 15 years);
• there are “MS clusters” — regions of sharply increased frequency of MS and “MS microepidemia” — a severe increase in the incidence of MS in a limited area in a certain time period;
• as shown in a number of regions, in neighboring countries, even within the same country, the prevalence and incidence of MS can vary significantly; it may result from the sum of hereditary, external and social factors.

There is a high-risk zone with a disease frequency of more than 50 per 100,000 population (Northern and Central Europe, southern Canada and northern USA, southern Australia and New Zealand). The medium-risk zone has a disease rate of 10-50 per 100,000 population and includes the center and south of the United States, the Hawaiian Islands, Southern Europe, Israel, Iran, the Middle East, South Africa, most of the regions of Russia including the southern regions, Siberia and the Far East. The low-risk zone with a frequency of 10 or less per 100,000 population includes a number of territories in Asia, northern South America, Central America, and most of Africa (except North Africa and South Africa).

The main trend in the epidemiology of MS in recent decades is thought to be a widespread increase in the prevalence and incidence. In Russia, in addition to the historically established high-risk areas for MS in the north and north-west of the country, high-risk areas in the south of the European part, in the central regions, the Volga region, Eastern Siberia and the Far East are described in this century. The main reasons for the increase in the frequency of MS are considered a true increase in the incidence, that is, the number of new cases, and the influence of medical and social factors (an increase in the average life expectancy of patients due to early correct diagnosis and improved treatment).

Etiology

Currently, MS is defined as a multifactorial disease, i.e., both external and hereditary factors are involved.

The following factors attract special attention of researchers:

• viruses (endogenous retroviruses, herpes groups, Epstein–Barr virus), bacterial infection (streptococcus, staphylococcus, etc.);
• chronic intoxication (organic solvents, gasoline, metals, other chemicals); stay in environmentally unfavorable living conditions, especially in childhood, plays a significant role;
• nutritional characteristics (in particular, the predominance of animal fats and proteins), especially at the age of 15 years, a lack of vitamin D both in food and due to insufficient insolation has a certain significance; changes in the intestinal microbiome in MS are also actively studied;
• convincing evidence has been obtained in favor of the role of smoking both as one of the factors that increase the risk of developing MS, and as a factor that aggravates its course;
• chronic psychoemotional stress; neuroimmunological and psychoimmunological mechanisms, which determine predisposition and characteristics of the MS are extensively studied.