Information about seasonal distribution of Neuromyelitis optica spectrum disorders (NMOSD) attacks have rarely been described and are non-conclusive.
To quantify the seasonal variation of relapses in Neuromyelitis Optica Spectrum Disorders in a country at the equator.
Descriptive retrospective cohort study between January 2008 and December 2019. Data of demographic and clinical information including relapses and follow up of all patients with NMOSD at Instituto Neurológico de Colombia (INDEC) were recorded. The annual, monthly and intra-annual seasonal variation of NMOSD relapses were quantified. Seasonal temporal variation was defined as first dry season (FDS) (January-March), first rainy season (FRS) (April-June), second dry season (SDS) (July-September) and second rainy season (SRS) (October-December).
There were 99 patients and 242 relapses (191 with data of the month of admission). The mean age was 45±14 and 90 (88%) were women. 87 (88%) patients were AQP4 Ab (+). Spinal cord 127 (52%) followed by optic neuritis 89 (36.5%) were the most common relapses. Attacks were treated with methylprednisolone 99 (54.5%) and methylprednisolone + plasmapheresis 56 (30.8%). Analysis of 191 relapses per month, showed higher frequency of attacks in November and December. The incidence of seasonal temporal variation (rainy or dry season) was FDS 21%, FRS 22.4%, SDS 26.2% and SRS 30.4% respectively. The incidence of relapses in rainy season compared to the dry season (52.8% vs 47.2%) was greater and this difference reached statistical significance (p= <0.05 U de Mann-Whitney).
NMOSD attacks tend to occur more frequently during the rainy season, further studies should focus on possible environmental risk factors as relapse triggers.