Multiple Sclerosis: Changing Trends in Latin Americans. Epidemiology and Regional Characteristics
Victor M. Rivera
Multiple Sclerosis (MS) is a multifactorial disease of the central nervous system (CNS) in which environmental factors interact with the immunological milieu of a genetically susceptible individual. MS is considered the second most common cause of neurological disability in the young adult after head trauma (1). Its complex challenges (from diagnosis to management) constitute a realistic public health concern in Latin America (LATAM), where the disease exerts an enormous socioeconomic burden despite its relatively low prevalence, considering the majority of these countries are emergent economies (2). The disease is highly prevalent among white Caucasian populations of northern European ancestry and racial groups derived from their genetic admixtures. MS has a distinct geographic distribution being more prominent in the northern and most southern areas of the globe. Its prevalence appears to increase by 0.33/100,000 inhabitants per each degree of latitude away from the equator’s line (3, 4). The reason for this tendency is not completely understood. Susceptible genetics affecting peoples living in the high risk areas appears to be a major factor (i.e. populations from Iceland, Scandinavian countries, the British Isles, north and central Europe, Canada, USA, New Zealand and Australia ). Other theories suggest as contributing factor decreased exposure to ultraviolet solar radiation (UVSR) in these areas, hence reduction of metabolic vitamin D utilization particlarly in the northern areas of the globe. Insufficient serum vitamin D (25-hydroxyvitamin D) levels have been associated to early conversion to “Clinically Definite MS” and to severity of disease (5). There is also evidence that MS may develop in individuals whose mothers were vitamin deficient during their pre-natal period (6). A link exists between the vitamin D coding genes and the MS propensity human leukocyte (HLA) DRB1 (7). Microbial agents particularly viruses of the herpes family (Epstein Barr, Human Herpes Virus-6 or HHV-6 and Varicella-Zoster) as well as the bacteria Chlamydia pneumoniae, have been proposed as environmental agents acting as non-self-antigens in the pathogenesis of MS contributing to the initiation of the erroneous inflammatory autoimmunological cascade that eventually damages the CNS, so characteristic of the disease (8). Most likely due to the introduction of high risk European genes into diverse world populations MS has become a universal disease affecting groups that were considered naïve to this disorder being transformed at present into susceptible cohorts. A clear example of this historical phenomenon is MS in LATAM. While MS prevalence has globally increased, a documented epidemiological augmentation has also affected the regional frequencies in the tropical countries of this hemisphere. This development is most likely influenced by several factors including utilization of modern criteria for diagnostic ascertainment (9), increasing access to MRI equipment and trained neurologists, and public awareness of a neurological condition that is no longer an exotic disease in the region.