Interstitial Lung Disease: Does It Represent a Real Comorbidity in Spondyloarthritis Patients? Results from an Ultrasound Monocentric Pilot Study

Background: Interstitial lung disease (ILD) is a frequent complication in rheumatoid arthritis (RA) where it represents the most common extra-articular involvement (with a prevalence of about 10-60%) and the second cause of mortality (after cardiovascular diseases). Spondyloarthritides (SpA) are chronic arthritides that share with RA both a similar disease burden and similar therapeutical approaches. ILD evaluation is challenging, given the low sensitivity of X-ray and pulmonary function tests, and radiation linked to repetitive HRCT. Lung Ultrasound (LUS) has shown potential in the evaluation of ILD in autoimmune diseases. Objectives: To assess the prevalence of ILD in a cohort of SpA patients (pts) using LUS with respect to healthy subjects (HS). Secondary aim is to assess possible correlations between ILD and clinical features in a cohort of SpA pts using LUS. Methods: Consecutive SpA out-patients were examined by LUS, applying the definition for pleural line irregularity (PLI) recently provided by the OMERACT taskforce for LUS in systemic sclerosis. Seventy-one intercostal spaces were studied (14 in the anterior chest, 27 lateral and 30 posterior) in all the pts/HS using an Esaote MyLab25 Gold US machine with a linear 7.5-10 MHz probe. A total pleural score was calculated. Each patient answered to Italian-validated PROs on respiratory function (Leicester and Saint-George), global health (SF-36) and dyspnea (mMRC scale). Clinical data on disease-duration, disease-onset, disease-activity (at the moment of the examination) and MTX/biologics treatment were collected from the medical records. Results: Seventy-three SpA pts (46 psoriatic arthritis -PsA- and 27 ankylosing spondylitis -AS-) and 56 HS were studied. No significant differences were demonstrated between groups (SpA vs HS and PsA vs AS) for age, sex, BMI and smoking habits. The total PLI score was significantly higher in SpA pts than in HS (p0.001). A positive correlation was found between total PLI score and PLI score from anterior, posterior and lateral chest. The posterior part of the chest showed a higher PLI score than the anterior and lateral one. No statistically significant differences were found between PsA and AS. MTX use was not a risk factor for PLI (no differences were found between SpA MTX+ and SpA MTX- patients). PROs (Leicester, Saint-George and SF-36) were not related to PLI total score. A significant correlation was found only between SF36 score and the presence of PLI in the anterior chest. PROs were instead related among them, showing a good concordance for absence/presence of symptoms. Disease activity, disease duration and age at disease-onset were not related to PLI total score. Smoking habit resulted to be predictive for a significant higher PLI score both in SpA patients and HS. Conclusions: LUS examination shows a higher amount of PLI in SpA with respect to HS. Smoking habit was the only clinical feature correlated to PLI on LUS examination in our population.