Seasons and ALS time of death

Respiratory complications are the main cause of death in amyotrophic lateral sclerosis (ALS). Season-associated-death risk was not addressed before.

To assess month/season-associated death risk in ALS.

We included all patients followed in our unit who died before 1 January 2016, excluding those with uncertain information. A χ² test assessed differences between months/seasons. A two-step cluster analysis explored the significant survival independent factors. Values of p < 0.05 or p < 0.01 (multiple comparisons) were considered significant.

From 778 patients, 543 had died at censor date. Absolute death number was 46,46,37,47,38,50,41,43,41,48,40,66, for each month from January to December. No significant difference existed when considering all months and seasons globally (p > 0.05). Significant differences were found comparing December (highest rate, 12.2%) with March, May, July, August, September, November (p < 0.05). Deaths were higher in winter than in spring (p = 0.031), but similar between winter and summer (p = 0.16), and winter and autumn (p = 0.087). Bulbar-onset patients had a relatively increased death rate in summer, while spinal-onset patients died more frequently in winter.

Death risk factors are probably dehydration for patients with dysphagia during summer and respiratory infections for patients with weak cough during winter. Flu vaccination, better ventilatory/cough assistance in winter and hydration in summer are recommended.