Impact of interstitial lung disease on the survival of systemic sclerosis with pulmonary arterial hypertension

To assess severity markers and outcomes of patients with systemic sclerosis (SSc) with or without pulmonary arterial hypertension (PAH-SSc/non-PAH-SSc), and the impact of interstitial lung disease (ILD) on PAH-SSc. Non-PAH-SSc patients from the Spanish SSc registry and PAH-SSc patients from the Spanish PAH registry were included. A total of 364 PAH-SSc and 1589 non-PAH-SSc patients were included. PAH-SSc patients had worse NYHA-functional class (NYHA-FC), worse forced vital capacity (FVC) (81.2 ± 20.6% vs 93.6 ± 20.6%, P < 0.001), worse tricuspid annular plane systolic excursion (TAPSE) (17.4 ± 5.2 mm vs 19.9 ± 6.7 mm, P < 0.001), higher incidence of pericardial effusion (30% vs 5.2%, P < 0.001) and similar prevalence of ILD (41.8% vs. 44.9%). In individuals with PAH-SSc, ILD was associated with worse hemodynamics and pulmonary function tests (PFT). Up-front combination therapy was used in 59.8% and 61.7% of patients with and without ILD, respectively. Five-year transplant-free survival rate was 41.1% in PAH-SSc patients and 93.9% in non-PAH-SSc patients (P < 0.001). Global survival of PAH-SSc patients was not affected by ILD regardless its severity. The multivariate survival analysis in PAH-SSc patients confirmed age at diagnosis, worse NYHA-FC, increased PVR, reduced DLCO, and lower management with up-front combination therapy as major risk factors. In conclusion, in PAH-SSc cohort risk of death was greatly increased by clinical, PFT, and hemodynamic factors, whereas it was decreased by up-front combination therapy. Concomitant ILD worsened hemodynamics and PFT in PAH-SSc but not survival regardless of FVC impairment.


Results
At the time of study inclusion, there were 1996 patients enrolled in the RESCLE and 3409 in the REHAP registries. Of these, 1589 (79.6%) RESCLE patients did not have a PAH diagnosis (non-PAH-SSc) and 364 (10.7%) REHAP patients had SSc (PAH-SSc) confirmed on RHC. RHC was only performed in 58 non-PAH-SSc patients ruling out this complication, and specifically in 6 out of 38 patients with sPAP > 40 mmHg by echocardiography. These were the populations analyzed. Autoantibody specificities were available in non-PAH-SSc patients, 687/1413 (48.6%) had anti-centromere antibody, 259/1386 (18.7%) had anti-topoisomerase I antibody and 42/353 (11.9%) had anti-RNA polymerase III antibody. Table 1 summarizes the baseline demographic, clinical, and echocardiography data of patients according to presence of PAH. Compared to non-PAH-SSc patients, PAH-SSc patients were older, had worse New York Heart Association functional class (NYHA FC) and pulmonary function tests (PFTs) (as assessed by % of predicted forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLCO)); more patients had FVC/DLCO ≥ 1.4 and even ≥ 1.6. Furthermore, mean systolic pulmonary artery pressure (sPAP) was greater in PAH-SSc patients, more patients presented sPAP > 40 mmHg, any grade or moderate-severe degree of tricuspid regurgitation, pericardial effusion, or lower tricuspid annular plane systolic excursion (TAPSE) values. No differences were observed in the prevalence of ILD. Regarding medical treatment, most PAH-SSc patients (62.6%) received up-front combination therapy while 15.9% non-PAH-SSc patients received specific vasodilators for peripheral vasculopathy. These differences did not change when the population was compared according to the presence or absence of ILD (online supplementary table II and III).

Discussion
By linking two nationwide registries this study, the largest conducted to date, further highlights the huge impact that PAH has on SSc patients. Approximately half of the patients were diagnosed with ILD independently of the presence of PAH. In PAH-SSc patients, ILD was found to worsen PFTs and hemodynamics but did not have a direct significant impact on survival, regardless of the severity of the ventilatory restrictive pattern. Older age, worse NYHA FC stages, higher PVR, and reduced DLCO at the time of diagnosis were independently linked to poor prognosis. Current treatment strategies (i.e., greater use of up-front combination therapy) are likely to have had an impact on survival of PAH-SSc patients even when they experienced mild-moderate ILD.
PAH-SSc patients had higher sPAP and tricuspid regurgitation velocity, were older, had worse NYHA FC, lower DLCO and elevated FVC/DLCO ratio (> 1.6 and 1.4), and greater prevalence of pericardial effusion; all of them well known clinical features of SSc-associated PAH. The devastating effect of PAH on SSc was reflected by a reduction of nearly 60% in 5-year transplant-free survival (41.1% vs. 93.9% in non-PAH-SSc patients). Three-year survival rate of PAH-SSc patients in our study (59.1%) was similar to that reported by other registries 9,19,24-28 and a meta-analysis performed by Lefevre et al. 29 . Only in the large prospective PHAROS study 3-year survival rate was higher (75%) 30 . This has been attributed to earlier diagnosis of PAH as reflected by the greater percentage of patients with NYHA FC I-II (59% vs. ~ 30% in the above-mentioned registries and in our series). Availability of new PAH-targeted therapies and treatment strategy changes during follow-up are also likely to affect survival. However, in the meta-analysis published by Lefevre et al. 29 survival did not change between studies over time, and disease's severity at baseline was the most important prognostic factor. Up to 60% of PAH-SSc patients in our series received up-front combination therapy in contrast to the 43% in the French registry and the 34% in  Patients with SSc-PH-ILD had lower FVC and lower DLCO. Use of first-line PAH-specific therapies was similar in both groups and included endothelin receptor antagonists (80%), phosphodiesterase 5 inhibitors (13%), or a combination of both (6%). Only 3 patients received a prostacyclin analog as initial treatment.
In our study, PAH-SSc patients with ILD and FVC ≥ 60% presented with FVC/DLCO ≥ 1.6 more frequently, indicating a more prominent vascular involvement in this subgroup. The threshold determining the extension of ILD leading to one or another classification PH group is blurred and remains to be defined. Thus, when patients present with precapillary PH and mild ILD they are classified into PH Group 1, and when they have more severe ILD they are classified into PH Group 3 (PH-ILD). Despite this fact, a significant proportion of patients present with intermediate severity of ILD and with different degrees of PH, which make PH classification and the following treatment decision especially challenging.
In this cohort, the worse hemodynamics and pulmonary capacity at PAH-SSc diagnosis associated with concomitant ILD did not turn into worse transplant-free survival, although a trend to higher 5-year survival was observed in patients with lower FVC. Previous studies have reported increased mortality in patients with PAH-SSc and ILD 15,29,34 , but most of them merged PAH-SSc patients with mild ILD (PH group 1) with PH-ILD patients. As in our series, Volkmann et al. reported similar 3-year survival rates in PAH-SSc patients with and without ILD (50% and 60%, respectively) 35 , which were associated with early use of aggressive treatment (i.e., prostanoid therapy was used in 52% of patients with ILD). Recently, Young et al. have described a prospective cohort of 93 patients with ILD, identifying a PH prevalence of 29 (31.2%) with a 3-year survival of 91% 36 . Such optimal survival may be explained by the intensive PH screening program and the extensive use of vasodilator therapy (82.8% of the patients with PH). Conversely, the survival in the French registry was significantly shorter in patients with SSc-PH-ILD compared to those with SSc-PAH. In SSc-PH-ILD patients, the survival rates at 1, 2, and 3 years were 91.9%, 78.8%, and 58.5%, respectively, compared to 95.9%, 91.3%, and 78.6% in SSc-PAH patients (P = 0.04) 33 .
A more conservative treatment approach with higher use of PAH monotherapy at diagnosis was observed for patients with ILD and FVC < 60%. This was probably due to safety concerns associated with the use of PAHtargeted therapies in patients with PH-ILD 18 as these latter patients have traditionally been excluded from PAH clinical trials 37 .
Facing the reality that we still cannot precisely classify PH-SSc when associated with ILD, there is increasing evidence suggesting that early use of pulmonary vasodilator treatment improves outcomes, and nationwide registries confirm a widespread off-label use of these drugs in real life, reflecting that treating PAH is a priority for clinicians irrespective of the severity of ILD. Our results reinforce this idea and indicate that treating PAH-SSc aggressively from onset improves outcomes regardless of the presence of ILD.
In PAH-SSc patients, prognostic factors identified in univariate survival analysis were similar to prior metaanalysis 29 , although lower FVC or DLCO, increased FVC/DLCO ratio ≥ 1.4, and lower use of up-front combination therapies at the time of PAH diagnosis were also identified as indicators of poorer survival. Interestingly, the presence of ILD or reduced FVC were not identified as risk factors in the multivariate analysis, whereas older age, worse NYHA FC, elevated PVR or reduced DLCO, and monotherapy at PAH diagnosis were associated to www.nature.com/scientificreports/ worse prognosis. Conversely, in the French PH registry only the presence of ILD, chronic kidney disease, and 6-min walk distance at baseline were associated with greater mortality 33 . Concerning the age at PAH diagnosis, the French national study conducted between 2006 and 2017, has described an improvement in survival in patients ≤ 70 years but not in older ones 28 . That may be explained by the higher proportion of patients that, in the later years, has been treated with pulmonary vasodilator up-front combination therapy both in the first 4 months Table 3. Factors associated to survival in univariate analyses. Significant values are in bold. † Parameter not included in the multivariate analysis as it was available in less than 60% of non-PAH-SSc patients. ‡ Parameter not included in the multivariate analysis as it was available in less than 60% of PAH-SSc patients. *All death patients in non-PAH-SSc had TAPSE ≥ 18 mm. www.nature.com/scientificreports/ (48.6% vs 25.6%) and throughout the study (64.3% vs 39%). Our results support the use of up-front combination therapy at early PAH diagnosis regardless of age in order to improve transplant-free survival. Several limitations have to be recognized in the interpretation of this study, some of them (e.g., only using variables common to both registries, not analyzing treatments during follow-up nor the last one reported) have been already noted. RHC was not performed for the selection of non-PAH-SSc patients due to it is an invasive procedure, and it is indicated after cautious doctor's decision. ILD-targeted therapy was not available in PAH-SSc cohort that may also influence on survival of this patients. Both registries are voluntary, which leads to a lack of information on variables that may impact prognosis. To mitigate this limitation, multivariable analysis was carried out using only variables available in > 60% of patients.

Conclusion
The largest assessment ever of the impact of PAH on SSc confirms the very relevant clinical and prognostic repercussion of PAH on SSc. When associated with ILD, PAH-SSc presents with worse hemodynamic features and PFTs, but not poorer survival independently of ILD severity. Baseline treatment with pulmonary vasodilator up-front combination therapy was established in a majority of PAH-SSc patients regardless of the presence of ILD and was independently associated with longer survival.

Materials and methods
Patients. Study design, inclusion and exclusion criteria, and data collection of RESCLE and REHAP registries have been published elsewhere 20,23 . All methods were carried out in accordance with relevant guidelines and regulations and the study was approved by the Hospital Vall d'Hebron Institutional Review Board [PR(AMI)280/2018]. In brief, RESCLE is a voluntary nationwide registry of patients with SSc diagnosed on the 2013 ACR/EULAR criteria for SSc 38 and/or on the modified LeRoy and Medsger classification criteria 39 . The onset of scleroderma was defined as the first symptom related to SSc including Raynaud's phenomenon. Both prevalent and incident non-PAH-SSc patients from RESCLE registry were included in the analysis, and excluding PH-SSc patients. REHAP is also a voluntary nationwide registry designed to prospectively collect exhaustive information on the demographics, management, and outcome of patients newly and previously diagnosed with PAH by RHC 23 . PAH was defined as a mean pulmonary arterial pressure (mPAP) ≥ 25 mmHg at rest with a pulmonary artery wedge pressure ≤ 15 mmHg and pulmonary vascular resistances ≥ 3 Wood units at RHC 32 . For the purposes of this study, only prospectively recruited incident patients with SSc-associated PAH (PAH-SSc) from REHAP registry were included in this analysis. Data collected. Baseline data from RESCLE and REHAP registries at the time of diagnosis of SSc and PAH respectively were collected. The following variables, considered potential risk factors for PAH in SSc [40][41][42] , were common to both registries and included in the analyses: (1) Demographics: age at the time of diagnosis (SSc or PAH) and gender 24,41 ; (2) Clinical: New York Heart Association functional class (NYHA FC) and time since SSc diagnosis 20,24,40,41 (only for RESCLE patients); (3) Pulmonary function test (PFT): predicted forced vital capacity (FVC %), predicted diffusing capacity for carbon monoxide (DLCO %) 24,40,41 and the FVC%/DLCO% ratio > 1.6 43 . We also evaluated a less restrictive cut-off value of 1.4, which has been associated to PH in patients with ILD 44,45 . ILD was defined as the presence of an interstitial pattern on high-resolution computed tomography (HRCT) in REHAP, and by HRCT or chest x-ray in RESCLE. Comparative analyses were performed only in patients with HRCT-confirmed ILD; (4) Echocardiography assessments: left ventricular ejection fraction (LVEF), systolic PAP (sPAP), degree of tricuspid regurgitation, pericardial effusion, and tricuspid annular plane systolic excursion (TAPSE) 24 ; (5) Causes of death, which were homogenized as both registries had different approaches of capturing these data (online supplementary table I). For the definition of independent prognostic factors in PAH-SSc and to analyze the impact of ILD on PAH-SSc, we also selected prognostic variables including 6-min walk test (6MWT), hemodynamic parameters (cardiac output [ Patient demographics, clinical variables, cardiac, and pulmonary assessments were prospectively recorded by participating physicians according to a standard protocol. Both registries required all patients to provide written informed consent in order to participate. The Institutional Review Boards of the participating hospitals approved the respective registries. Statistical analyses. Continuous variables were summarized as the mean ± SD or the median and interquartile range (IQR) as appropriate and compared using Student's t-test or Mann-Whitney U test, respectively. Categorical variables were compared using the chi-square and Fisher's exact tests as appropriate. P values < 0.05 (2-tailed) were considered significant. Bonferroni correction was applied in multiple comparisons. Patients lost to follow-up were censored on the day of their last visit. Time-to-event analyses were performed using the Kaplan-Meier method until date of lung transplantation or death. Transplant-free survival was estimated since the time of SSc diagnosis in non-PAH-SSc patients, and since PAH diagnosis in PAH-SSc patients. Factors associated with worse prognosis were identified using the Cox proportional hazards models. Variables collected in > 60% of patients that were found to be significant in univariate analysis (P < 0.05) were incorporated into a step-wise multivariate model.

Data availability
The data that support the findings of this study are available on request from the corresponding author.