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

<b>Background/Objectives:</b> Interstitial lung disease (ILD) is a frequent complication of rheumatoid arthritis (RA), representing the most common extra-articular manifestation (with a prevalence of about 10-60%) and the second cause of mortality. Spondyloarthritides (SpAs) are chronic arthritides that share with RA both a similar disease burden and similar therapeutical approaches. The evaluation of ILD is challenging, given the low sensitivity of X-ray and pulmonary function tests, and the radiation exposure linked to repetitive HRCT. Lung ultrasound (LUS) has shown potential in the evaluation of ILD in autoimmune diseases. The purpose of this study is to assess the prevalence of ILD in a cohort of SpA patients (pts) using LUS in comparison with healthy subjects (HSs). The secondary aim is to evaluate potential correlations between ILD and clinical features within the SpA cohort using LUS. <b>Methods:</b> 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 methotrexate (MTX) or biologics treatment were collected from the medical records. <b>Results:</b> 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 (<i>p</i> < 0.001). A positive correlation was found between the total PLI score and the PLI score from anterior, posterior and lateral chest. The posterior region of the chest showed a higher PLI score than the anterior and lateral regions. 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 the PLI total score. A significant correlation was found only between the SF36 score and the presence of PLI in the anterior chest. PROs were instead correlated with each other, 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 was found to be predictive of a significantly higher PLI score both in SpA patients and HSs. <b>Conclusions:</b> LUS examination shows a higher amount of PLI in SpA patients with respect to HSs. Smoking habit was the only clinical feature correlated to PLI on LUS examination in our population.