Motor Neuron Disease is not clustered or associated with socioeconomic deprivation in Scotland

Background and Objectives Understanding risk factors and spatial variation of risk may provide insights into the pathological mechanism of motor neuron disease (MND). Socioeconomic status (SES) has been hypothesised as a risk factor, but results from previous studies are inconsistent. No spatial epidemiology studies examining geographic clustering of MND have been performed in Scotland to date. We investigated the effect of SES and geography on MND risk in Scotland using the highly curated and nationally representative Scottish MND Register (CARE-MND) that has over 95% case ascertainment. Methods Patients on the Scottish Clinical Audit Research Evaluation for Motor Neurone Disease platform, with date of diagnosis between 01 Jan 2015 and 28 Feb 2021 were included and geocoded with data zones using their residence at diagnosis. Indirectly standardised incidence ratio (SIR) accounting for age and sex was calculated for each health board. Poisson regression was used to examine the effect of SES on MND risk, adjusted for age and sex of population at risk. Geographic clustering was assessed using global Moran’s Index, Bayesian conditional autoregressive models and SaTScan software. Results Among 1149 patients included, 1126 (98%) were successfully geocoded. Significantly lower SIR was shown in Highland (0.60, 95% CI 0.44 – 0.80, p <0.001). After adjusting for age and sex in Poisson regression, there was no significant effect of SES on MND risk. Moran’s Index indicated a weak but significant spatial autocorrelation (I=0.017, p =0.008). However, risk maps using Bayesian modelling showed a relatively homogeneous distribution without distinct patterns across Scotland. Similarly, SaTScan did not detect any significant cluster of high or low risks. Discussion Our findings support the notion that MND risk is mostly random-distributed and independent of SES in Scotland. Our results are generalizable to other MND populations.