Course of Itch from Systemic Sclerosis Onset: a Scleroderma Patient-Centred Intervention Network Cohort Longitudinal Study

ABSTRACT Background Itch in systemic sclerosis (SSc) is thought to be most significant in early disease, but no longitudinal studies have examined itch course. We estimated itch presence and severity from SSc disease onset, accounting for participant age and time since onset at each assessment. Methods People with SSc from the multinational Scleroderma Patient-centred Intervention Network Cohort completed past-week itch severity assessments (0 to 10 numerical rating scale) at enrolment and longitudinally at 3-month intervals. To estimate itch probability (score > 0) and, if present, itch severity, we used two-stage mixed effects models with basis splines to address non-linearity. The primary predictor was age at each assessment, partitioned into age at non-Raynaud phenomenon symptom onset and time since onset. We estimated prevalence and severity for onset ages of 20, 30, 40, 50 and 60 years and, for each onset age, at 2 years, 3 years, 4 years, 5 years, 7 years, and 5-year intervals 10 years to 35 years post-onset. Findings We included 2173 participants with 19 733 itch assessments (mean [standard deviation] 9·1 [6·9] assessments). 1896 of 2173 (87·3%) participants were women. Mean age at enrolment was 54·7 (SD 12·7) years. 873 (40·2%) participants had diffuse cutaneous SSc. Predicted itch probability was between 35·0% (95% CI 31·8% to 38·5%) and 36·8% (95% CI 33·3% to 40·4%) at all onset age and disease duration combinations. Mean itch severity, when present, was moderate, between 4·1 (95% CI 4·1 to 4·1) and 4·4 (95% CI 4·3 to 4·4), for all age and duration combinations. Interpretation Itch prevalence and mean severity were stable across onset ages and over time within onset ages. Findings suggest that itch is common in SSc and not as closely related to disease duration as previously thought. Research is needed to elucidate itch pathophysiology and identify effective management strategies. Funding Funding for the study was provided by a Skin Investigation Network of Canada Team Development Award. Funding for the Scleroderma Patient-centred Intervention Network Cohort has been received from the Canadian Institutes of Health Research (TR3-119192; PJT-149073; PJT-148504; PJT-195879; PJT-203755); the Arthritis Society; the Lady Davis Institute for Medical Research of the Jewish General Hospital, Montréal, Québec, Canada; the Jewish General Hospital Foundation, Montréal, Québec, Canada; McGill University, Montréal, Québec, Canada Scleroderma Society of Ontario; Scleroderma Canada; Sclérodermie Québec; Scleroderma Manitoba; Scleroderma Atlantic; the Scleroderma Association of BC; Scleroderma SASK; Scleroderma Australia; Scleroderma New South Wales; Scleroderma Victoria; and the Scleroderma Foundation of California. RESEARCH IN CONTEXT Evidence before this study We searched PubMed using the terms “itch” or “pruritus” with “systemic sclerosis” or “scleroderma” on March 26, 2025, to identify previous studies that have evaluated the trajectory of itch prevalence or severity in systemic sclerosis (SSc) from the time of disease onset. We did not find any longitudinal studies. We identified 4 cross-sectional studies, and none found statistically significant associations between disease duration and itch. Three of the studies included between 56 and 126 participants. The fourth study included 959 participants and found that itch was experienced on most days in the last month based on a single dichotomous item among 46% of participants between 1 and 4·9 years since non-Raynaud phenomenon (non-RP) symptom onset and 41% for those 5 or more years since onset (not statistically significant). Added value of this study This was the first longitudinal study of itch prevalence and severity in SSc. We evaluated 2173 Scleroderma Patient-Centred Intervention Network participants from 7 countries who reported itch severity in the past week (0 to 10 numerical rating scale) at cohort enrolment and subsequently at 3-month intervals (19 733 total itch assessments). We simultaneously modelled probability of having any itch and, if present, itch severity. We accounted for both normal aging and SSc disease duration by including age of onset of non-RP symptoms and time since onset in our models. We found that itch prevalence and mean severity were stable across the course of the disease. Between 35% and 37% of participants reported itch (numerical rating scale score > 0) across all ages of onset and time since onset combinations. Mean itch severity, among participants with itch, was between 4·1 and 4·4 points, a moderate level, at all onset age and disease duration combinations. Findings were consistent for subgroups defined by participant country, sex, and diffuse versus limited cutaneous SSc. Implications of all the available evidence Itch is rarely researched in SSc, and itch assessment and management are typically not part of routine SSc care. It is commonly assumed that itch is most prominent, if present, in early disease. Our study showed that, contrary to this assumption, itch is present for many people with SSc across the course of the disease; itch prevalence and mean severity were stable across time regardless of age of SSc onset. Findings from our study underline the need for research on the pathogenesis of itch in SSc and the development and testing of treatments. Itch assessment and management should be part of routine SSc care.