Seasonal variations of systemic lupus erythematosus flares in southern France.

Objective: Exposure to sunlight is one of the environmental factors involved in the pathogenesis of systemic lupus erythematosus. We investigated whether there is seasonal variation in the incidence of cutaneous and noncutaneous severe lupus flares in southern France.

Methods: We retrospectively reviewed clinical and biological data from all SLE patients hospitalized for a flare of the disease during a two year period in our centre and collected corresponding meteorological data from the official website of MeteoFrance.

Results: Forty one patients, mean age 36.7 ± 13.8 years, were included. Twenty-six patients (63.4%) had kidney biopsy performed, showing in all cases proliferative nephritis, associated with membranous nephritis in 9 (22%). We found a clear seasonal pattern for overall lupus flares with 39% of flares occurred in Spring. Among patients without any cutaneous involvement, this seasonal pattern was still observed (p=0.024). Patients under antimalarials presented flares significantly later in the sunny season than those without (respectively median in July versus May, p=0.044). There were strong positive correlations between occurrence of lupus flares and maximum temperature increase (ρ=0.87, p<0.001), minimum temperature increase (ρ=0.87, p<0.001), and duration of sunshine increase (ρ=0.78, p=0.003). These correlations were also observed in patients with renal flares.

Conclusion: We confirmed a seasonal pattern for lupus flares among patients living in Southern France, with most flares in spring, in correlation with an increase in temperature and duration of sunshine. A similar seasonal pattern was observed in patients with no cutaneous involvement and with visceral involvement.