The association of outdoor temperature and self-reported Raynaud's phenomenon severity among people with systemic sclerosis: a Scleroderma Patient-centered Intervention Network Cohort study

Background:
Raynaud's phenomenon is the earliest and most common systemic sclerosis manifestation. Episodes can be triggered by cold exposure and ambient temperature changes. Small studies have found that Raynaud's phenomenon outcomes were associated with season. We aimed to map the degree that differences in ambient temperature are associated with Raynaud's phenomenon outcomes across the temperature spectrum.

Methods:
People with Raynaud's phenomenon secondary to systemic sclerosis in the Scleroderma Patient-centered Intervention Network Cohort completed past-week Raynaud's phenomenon severity assessments (0–10 numerical rating scale) at enrolment and longitudinally at 3-month intervals. Mean daily temperature and feels like temperature, which incorporates wind chill and humidity, for the week before each assessment were extracted for each participant from a weather site close to the participant's recruiting centre via the Iowa Environmental Mesonet. We used linear mixed models with basis splines to flexibly model non-linear changes in Raynaud's phenomenon severity across the temperature spectrum. People with lived experience of systemic sclerosis contributed to the study design and interpretation.

Findings:
Between April 15, 2014 and Aug 1, 2023, we included data on 20 233 Raynaud's phenomenon severity assessments from 2243 participants. 1964 (88%) of 2243 participants were women, 279 (12%) were men, and 1813 (82%) were White. Mean age was 54·8 (SD 12·7) years. The maximum predicted Raynaud's phenomenon severity score was 6·8 points (95% CI 5·6–8·1), which occurred at –25°C. Severity scores decreased minimally from –15°C to 5°C (0·05–0·21 points per 5°C difference), then decreased in larger steps between 5°C and 25°C (0·37–0·54 points per 5°C difference). The minimum predicted score was at 25°C (2·6 points [95% CI 2·5–2·7]). Scores increased at temperatures above 25°C to 3·5 points (3·0–4·1) at 35°C and 5·6 points (4·5–6·8) at 40°C. Results were similar for feels like temperature.

Interpretation:
Raynaud's phenomenon severity is worst at very cold temperatures but also increases with very warm temperatures, presumably due to air conditioning. Clinical management and Raynaud's phenomenon intervention trial designs should consider temperature patterns.

Funding:
Scleroderma Society of Ontario, Scleroderma Canada, Sclérodermie Québec, Scleroderma Manitoba, Scleroderma Atlantic, Scleroderma Association of BC, Scleroderma SASK, Scleroderma Australia, Scleroderma New South Wales, Scleroderma Victoria, the Canadian Institutes of Health Research, the Arthritis Society, the Lady Davis Institute for Medical Research of the Jewish General Hospital, the Jewish General Hospital Foundation, and McGill University.