Survival analysis of geospatial factors in the Irish ALS cohort

Abstract

Variations in environmental risk factors potentially influence incidence and progression in complex multifactorial diseases. Few studies have examined the association of survival in amyotrophic lateral sclerosis (ALS) with environmental geospatial variables. Here we use data from the Irish ALS cohort to perform such an analysis. Geographic data sources were used to generate small area values for four geospatial variables (population density, social deprivation, distance to coast, and distance to ALS multidisciplinary (MDT) clinic) for each ALS case on the Irish ALS register. These were combined with follow-up data and used as covariates in Royston-Parmar regression survival analysis including age of onset, site of onset, diagnostic delay, riluzole prescription and MDT clinic attendance as covariates. One thousand, two hundred and thirty-two patients with median survival of 2.31 years from disease onset were included. After addition of the individual geospatial variables in turn, none of the four variables was found to be associated with survival with a p-value <0.05. The results may reflect the public healthcare system that provides riluzole prescription and access to the MDT to all patients free of charge, and is also congruent with our recent finding that social deprivation is not associated with ALS incidence in Ireland.

Key words:

• ALS
• spatial epidemiology
• survival
• geospatial variables
• prognosis
• environment

Acknowledgements

James Rooney was funded by the Health Research Programme Clinical Fellowship Programme. Miriam Galvin and Katy Tobin are HRB Interdisciplinary Capacity Enchancement Fellows.

Orla Hardiman is funded by the Health Research Board Clinician Scientist Programme. She has received speaking honoraria from Novartis, Biogen Idec, Sanofi Aventis and Merck-Serono. She has been a member of advisory panels for Biogen Idec, Allergen, Ono Pharmaceuticals, Novartis, Cytokinetics and Sanofi Aventis. OH serves as Editor-in-Chief of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia.

The research leading to these results has received funding from the Health Research Board Interdisciplinary Capacity Enhancement Programme, the European Community's Seventh Framework Programme (FP7/2007-2013) under the Health Cooperation programme and the project EUROMOTOR (n°259867), from the European Joint Progamme in Neurodegeneration(SOPHIA and ALS-CarE) and the Charities Research Motor Neurone and Irish Motor Neurone Disease Association. The funding sources played no role in the preparation of this manuscript.