The epidemiology of interstitial lung disease (ILD) in systemic sclerosis (SSc) in Belgium is unknown. In literature, its prevalence varies between 19% and 52% in limited/diffuse cutaneous SSc (LcSSc/DcSSc). However, its prevalence in "early" SSc (pre-clinically overt SSc without [yet] skin involvement), nor its incidence rate in SSc (LcSSc/DcSSc/"early" SSc) has ever been described. Against this background, we aimed to determine the prevalence/incidence (rate) and progression of ILD in SSc.
12-year follow-up data of consecutive SSc patients, included in two Flemish cohorts (University Hospitals Ghent and Leuven), were retrospectively analysed. ILD was classified according to the simplified Goh algorithm. Progression of ILD was defined as a relative decline of FVC ≥10%, a combined relative decline of FVC 5-10% and DLCO ≥15%, or as an increase in HRCT extent.
722 patients (60% LcSSc/ 20% DcSSc/ 20% "early" SSc, median (IQR) follow-up 39 [12-80] months) had baseline HRCT. 243 were rated to have ILD at baseline and 39 during follow-up (prevalence of 34%/ incidence rate of 20.3/1000PY, 95%CI:14.5-27.8). Amongst those with baseline ILD, 60% had lung functional progression at five years of follow-up. In the "early" SSc subgroup, eight patients were rated to have ILD at baseline and three during follow-up (prevalence of 6%/ incidence rate of 5.8/1000 PY, 95%CI:1.2-17.0).
Both LcSSc and DcSSc patients should be monitored for ILD evolution. The low prevalence and incidence of ILD in the "early" SSc subgroup may instruct future decisions on the construction of uniform patient follow-up pathways in "early" SSc.