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September 1, 2010

Low prevalence of Multiple Sclerosis in Ecuador: an ethnic factor?

Multiple sclerosis (MS) is a debilitating autoimmune disease, although some new studies have raised the possibility that there is more than one pathway to the final pathological changes, and that different pathways may predominate in different clinical forms of MS. It has two major components, ie, axonal degeneration and inflammation, resulting in loss of the myelin-coated axons in the central nervous system (CNS).  MS is most commonly seen in the adult Caucasian population of Western European ethnic origin,  and most frequently affects women aged 20–40 years.4 A definite diagnosis of MS requires the occurrence of at least two neurological events consistent with demyelination that are separated both anatomically in the CNS and temporally. There are three clinical forms of the disease, the most common being the relapsing–remitting form (RRMS), which is characterized by episodes of neurological impairment followed by complete or nearly complete recovery. 

Prevalence: Globally, the median estimated prevalence of MS is 30 per 100,000, with a range of 5–80. Regionally, the median estimated prevalence of MS is highest in Europe at 80 per 100,000, followed by the Eastern Mediterranean (14.9 per 100,000), and the US (8.3 per 100,000). The countries reporting the highest estimated prevalence of MS are Hungary (176 per 100,000), Slovenia (150), Germany (149), and the US (135). The total estimated female:male ratio is around 2.0, and the prevalence rates reported are higher for women.  Other studies in the US have reported a prevalence of 58–95 per 100,000.  Moreover, in the past 25 years, prevalence studies of specific US regions have produced a range of estimates, up to 177 per 100,000 in Olmstead County, Minnesota.

Incidence: Globally, the median incidence of MS is 2.5 per 100,000. Regionally, the median estimated incidence of MS is greatest in Europe (3.8 per 100,000), followed by the Eastern Mediterranean (2), and the US (1.5). The countries reporting the highest estimated incidence of MS include Croatia (29), Iceland (10), and Hungary (9.8).

An interesting paper published by Patricio Abad and collegues showed that the prevalence of MS in Ecuador goes from 0.75 to 5.05 per 100,000 inhabitants being most frequent in Quito. The paper is:

Abad P, Pérez M, Castro E, Alarcón T, Santibáñez R, Díaz F. Prevalence of multiple sclerosis in Ecuador. Neurologia. 2010 Jul;25(5):309-313.

Abstract
Introduction: Multiple sclerosis (MS) is less frequent in areas near to the Equator, while the incidence and prevalence rises with increasing distance from this particular area, determining a clear north to south gradient. During the last decade several published reports provide recent data on the prevalence in Latin America. The main objective of this article is to report prevalence data in the three largest cities of Ecuador, a South American Country located on Latitude zero North-South.
Methods: In order to determine the prevalence and other epidemiological variables we conducted a cross-sectional, observational study in the three largest cities of Ecuador. Based on capture and recapture methodology we identified patients with MS who received medical care in the 12 state and private hospitals and in the Ecuadorian Foundation of Multiple Sclerosis (FUNDEM-Quito). The main inclusion criteria to determine the diagnosis of MS was based on the criteria proposed by Poser. For the relative and absolute frequencies calculation, as well as the 95% confidence interval, the EpiInfo 6.01 and EpiDat 3.1. programs were used.
Results: A total of 159 patients were identified in the three largest cities included in the study. In Quito, the capital city: 5.05/100,000 inhabitants (95% CI, 4.03-6.03), Guayaquil, on the coast: 2.26/100,000 inhabitants (95% CI, 1.62-2.91) and Cuenca in the south: 0.75/100,000 inhabitants (95% CI, 0.024-0.175).
Conclusions: Ecuador is a low prevalence country although we believe it is possible that the number of MS cases is underestimated since this is not a population based study. We believe that more studies should be carried out on general populations where the disease has been seldom reported or as non-existent. Important exogenous factors may be involved in the pathogenesis of MS in Ecuador.

Here the abstract in Spanish…
Abad P, Pérez M, Castro E, Alarcón T, Santibáñez R, Díaz F. Prevalence of multiple sclerosis in Ecuador. Neurologia. 2010 Jul;25(5):309-313.

Resumen
Introducción: La esclerosis múltiple (EM) es menos frecuente en las áreas cercanas a la línea ecuatorial, mientras que la incidencia y la prevalencia aumentan conforme se alejan de estas áreas, creando un gradiente norte-sur bien definido. Reportes publicados en la última década proveen datos recientes de la prevalencia en Latinoamérica. El objetivo de este artículo es comunicar las cifras de prevalencia en las tres ciudades más importantes del Ecuador, país localizado en la misma línea ecuatorial latitud N0-S0.
Métodos: Se realizó un estudio observacional transversal en un determinado periodo con el fin de determinar la prevalencia y otras características epidemiológicas de la EM en 12 hospitales de tercer nivel en las tres ciudades principales de Ecuador. Basados en el método captura y recaptura y utilizando una encuesta, se procedió a identificar los pacientes con EM que cumplen los criterios señalados por Poser y que acuden a los principales hospitales estatales, privados y a la Fundación Ecuatoriana de Esclerosis Múltiple (FUNDEM-Quito). Para el cálculo de frecuencias absolutas y relativas, comparación de porcentajes e intervalos de confianza (IC) del 95% se utilizaron los programas EpiInfo 6.01 y EpiDat 3.1.
Resultados: Se identificó a 159 pacientes en las ciudades donde se llevó a cabo el estudio. Quito, la ciudad capital, 5,05/100.000 habitantes (IC del 95%, 4,03-6,03); Guayaquil, en la costa, 2,26/100.000 habitantes (IC del 95%, 1,62-2,91); Cuenca, en el sur, 0,75/100.000 habitantes (IC del 95%, 0,024-0,175).
Conclusiones: Ecuador es un país de baja prevalencia, aunque creemos que hay un subregistro importante del número de pacientes, ya que éste no es un estudio poblacional. Creemos que se deben realizar estudios de prevalencia en poblaciones abiertas y en áreas en que la enfermedad es rara o inexistente. Importantes factores exógenos parecen estar involucrados en la patogénesis de la EM en Ecuador.

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