Epidemiological studies of multiple sclerosis in a Sardinian population, insular Italy : cluster studies and health status
Pugliatti, M.; Riise, T.; Nortvedt, M.; Carpentras, G.; Sotgiu, M. A.; Sotgiu, S.; Rosati, G.; Self-perceived physical functioning and health status in fully ambulatory MS patients. Preprint. Accepted for publication in Journal of Neurology. Published by Springer-Verlag. (368.3Kb)
American Journal of Epidemiology 164, Pugliatti, M.; Riise, T.; Sotgiu, M. A.; Satta, W. M.; Sotgiu, S.; Pirastru, M. I.; Rosati, G., Evidence of early childhood as the susceptibility period in multiple sclerosis. Space-time cluster analysis in a Sardinian population, pp. 326-333. Copyright 2006 Oxford University press. http://dx.doi.org/10.1093/aje/kwj190 (107.3Kb)
Neuroepidemiology 25, Pugliatti, M.; Riise, T.; Sotgiu, M. A.; Sotgiu, S.; Satta, W. M.; Mannu, L.; Sanna, G.; Rosati, G., Increasing incidence of multiple sclerosis in the province of Sassari, northern Sardinia, pp. 129-134. Copyright 2005 S. Karger AG. This article is copyright protected. Any distribution without written consent from S.Karger AG, Basel is a violation of the copyright. http://dx.doi.org/10.1159/000086677 (167.4Kb)
Neurology 58, Pugliatti, M.; Solinas, G.; Sotgiu, S.; Castiglia, P.; Rosati, G., Multiple sclerosis distribution in northern Sardinia: spatial cluster analysis of prevalence, pp. 277-282. Copyright © 2002 by AAN Enterprises, Inc. Copyright 2002 Lippincott, Williams & Wilkins. (241.9Kb)
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MS is a disorder of the central nervous system, manifesting as acute focal inflammatory demyelination and axonal loss, and culminating with chronic multifocal sclerotic plaques. MS involves several nervous functional systems resulting in disability, has a rather unpredictable course, and thus leads to poorer quality of life. It is a disorder of young adults, and the most common cause of non post-traumatic neurological disability. It is believed to be caused by interplay between genes and the environment. Potentially any environmental agent can have a role in determining MS in susceptible populations and yet be neither a necessary nor a sufficient cause. Potential risk factors have been investigated, such as infectious agents, vaccines, stress, occupation, climate and nutrition. At what age in a genetically predisposed individual’s life, exogenous factors can interact to initiate MS is rather controversial, although this probably occurs within the first 15 years of life. The present work involves two broad areas in MS research: (i) epidemiological descriptive studies aimed at disclosing clues to disease etiology and mechanisms of disease induction, and (ii) the study of determinants of health-related quality of life in the MS population at large. The specific objectives to this work were: to disclose MS variation at a microgeographic level, as a possible expression of the spatial distribution of disease risk factor(s) (Paper I); to update and characterise MS incidence patterns, as a possible expression of temporal distribution of disease risk factor(s) (Paper II); to assess whether individuals that later develop MS have shared the same environment at the same age indicating common exposure to disease factor(s), and if so at what age has this occurred (Paper III); and to compare the self-perceived health status to the general population, with special regards to physical functioning, in MS patients with no or mild disability as objectively measured (Paper IV). All these studies have been conducted on the province of Sassari, northern Sardinia, insular Italy (450,000 pop. circa) based on a registry system of MS cases. Epidemiological studies conducted over the past two decades using repeated assessments have shown that Sardinia is at high risk for MS with a prevalence of 150 per 100,000 and an annual mean incidence of 6 per 100,000. To investigate the distribution of MS in Sardinia at microgeographic level a spatial analysis of the disease prevalence in the study area for year 1997 was conducted (Paper I). To overcome random variability due to small numbers of cases per geographic unit, a hierarchical Bayesian approach was adopted. Spatial clustering patterns in the province south-west and a west-to-east gradient were observed. An incidence study was performed on 689 MS patients with disease onset between 1965 and 1999 in the study area (Paper II). The mean annual incidence rate increased significantly from 1 per 100,000 pop in 1965–69 to 6 in 1995–99, with no differences for gender and province sub-areas. The mean age at onset increased significantly during the same period from 25.7 to 30.6 years, while the proportion of patients with progressive initial course declined over time. Space-time cluster analysis was performed in the study area to indicate a possible shared exposure to MS risk(s) factors during the disease latent period, and the individuals’ age for this susceptibility period (Paper III). Residence changes from birth to clinical onset were recorded for all MS patients with clinical onset between 1965 and 1999 in the study area. Closeness in space and time was defined as living in the same commune, at the same time and at the same age differing only by 1, 2 or 5 years. The analysis was performed from birth until age 25 years or disease clinical onset, and by demographic and clinical subgroups. Clustering was substantial in early childhood. It was most marked in the most recent cases, among women and in patients with relapsing-remitting course. No clustering was found when closeness in time was defined as a fixed number of years before onset, arguing against a fixed latency period of the disease. MS heterogeneous spatial distribution at microgeographic level, its increased incidence and change of clinico-demographic phenotypes over a relatively short period of time, and evidences of clustering in space and time in early childhood especially occurring recently, are suggestive for the action of an exogenous factor(s) in determining MS. Ecological and case-control studies need to be designed and implemented to validate and characterise these observations. The self-perceived health status among MS patients with no or mild disability according to EDSS and the impact of self-rated physical functioning have been compared between a sample of fully ambulatory (EDSS ≤3.5) MS patients and the general population (Paper IV). SF-36 was used to self-rate health status. The 197 MS patients analysed (150 women and 47 men) had significantly lower mean SF-36 scores than the general population, except for bodily pain. Similar results were found for a sub sample of 107 patients (81 women and 26 men) with even lower disability (EDSS ≤2.0). EDSS correlated weakly with the physical functioning subscale, explaining only 2% of the variance in such SF-36 subscale. The regression of the physical functioning subscale on the other seven SF-36 subscales was significantly lower among MS patients than in the general population for all subscales, except for role limitation due to physical health problems and social functioning. Therefore factors other than physical functioning contribute to the low scores for the other dimensions compared with the general population. Neither disease course nor duration correlated significantly with SF-36 subscales. Strategies targeting a broad spectrum of health related issues for MS patients should be implemented starting already in the disease early stage. For cost-of-illness studies these findings provide clues to indicators to the disease socio-economic burden in the early stages, and elements for disease-specific interventions.