Longitudinal study of multiple scherosis in southern Tasmania : description of cohort and impact of demographic, disease, individual and lifestyle factors on clinical multiple sclerosis disability and progression

This thesis presents results of a prevalence survey and longitudinal cohort study (2002 to 2005) of people with clinically definite Multiple Sclerosis (MS) resident in Southern Tasmania (62-telephone area code). Case ascertainment was from multiple sources. In the longitudinal study, exposures included demographic (eg gender), disease (e.g. MS course), individual (e.g. BMI) and lifestyle (e.g. smoking) characteristics. Clinical outcome measures included the Expanded Disability Status Scale, Multiple Sclerosis Severity Score, Scripps Neurological Rating Scale and Multiple Sclerosis Functional Composite. Participants were reviewed face-to-face at baseline and 6 monthly thereafter during winter and summer. Questionnaires were filled and blood samples taken at every review. Clinical outcome measures were assessed at baseline and during subsequent winter reviews. The aim of this report was to identify the prevalence of MS in Southern Tasmania, to assess whether the longitudinal cohort was representative and to determine whether various exposures influenced clinical MS disability. Univariate linear regression and generalised estimator equations (GEE) models were used to examine associations between exposures and clinical outcomes. Adjustment for confounders was conducted for significant associations. On census day (7/08/2001) 256 cases were identified in the study region which had an eligible source population of 223 602, giving a crude prevalence rate of 114.5/100 OOO. In total 198 people (70% of eligible individuals) were recruited to the longitudinal study. Over 90% of participants remained in the study from their initial review to study end. Several novel results were obtained regarding exposure and MS disability. Highest level of education completed at baseline was negatively associated with disability (population average EDSS coefficient -0.57, 95% Cl -1.15 to -0.00, P<0.05, adjusted GEE model) and progression (annual change EDSS coefficient -0.22, 95% Cl -0.37 to -0.06, P<0.05, adjusted GEE model). Overweight participants had faster disease progression over the study period (annual change EDSS coefficient 0.19, 95% Cl 0.02 to 0.35, P<0.05, adjusted GEE model). Level of smoking during the study period was positively associated with disease progression. Participants born in summer progressed more than those born in other seasons with level of in utero UVR exposure during the third trimester negatively associated with MS disability. Females who were >13 years old at menarche were less disabled and had slower disease progression. In conclusion, this thesis demonstrates that the prevalence of MS in Southern Tasmania has increased, that several modifiable factors hasten MS progression and that exposures in early life may impact on MS progression.