Spatial clustering of motor neuron disease mortality in Western Mediterranean countries, 2003–2022

Background

Motor neuron diseases (MND) are a group of rare, progressive neurodegenerative disorders with marked geographic variability, suggesting the potential influence of environmental and contextual factors. However, evidence on spatial patterns at a high geographical resolution in Europe remains limited. This study aims to assess the spatial distribution and clustering of MND mortality across Western Mediterranean Europe.

Methods

Mortality data (ICD-10: G12.2) from 2003–2022 were obtained for France, Italy, Spain, and Portugal at the NUTS3 level (n = 288 regions). Age-standardized mortality rates and standardized mortality ratios were calculated. Spatial autocorrelation was assessed using Moran’s I (spatial autocorrelation measure), and local clustering was identified using Local Indicators of Spatial Association.

Results

Mortality rates increased over time in all countries, particularly in Portugal. A strong and significant spatial autocorrelation was observed (Moran’s I = 0.62, p < 0.001), indicating a non-random spatial distribution. Clustering was slightly more pronounced in men (I = 0.60) than in women (I = 0.53). Local spatial analysis identified significant high-risk clusters in northwestern France and central regions, while extensive low-risk clusters were observed across Spain and different parts of Portugal. These patterns were consistent in both sexes, although clustering was clearly defined in men, whereas women showed a more diffuse spatial distribution with a higher presence of local outliers, particularly in Italy.

Conclusions

MND mortality shows a clear and non-random spatial structure across Western Mediterranean Europe, with consistent clusters of high and low risk. These findings support the hypothesis that shared environmental or territorial factors may contribute to the geographic distribution of the disease. Further research is needed to explore potential environmental exposures underlying these patterns.

Key messages

• MND mortality shows strong spatial clustering (Moran’s I = 0.62), highlighting geographic inequalities across Western Mediterranean populations.

• Persistent high- and low-risk clusters suggest environmental and territorial determinants relevant for targeted public health action.