Combined Growth Differentiation Factor-15 (GDF-15) and Lung Ultrasound for ILD Screening in Rheumatoid Arthritis and Systemic Sclerosis

Overview

The goal of this observational study is to detect the lung affection in patients with Rheumatoid Arthritis(RA) or Systemic sclerosis (SSc) before appearance of symptoms(Subclinical) using combined diagnostic modalities which are Lung Ultrasound and a blood marker called Growth Differentiation Factor-15 (GDF-15). The main question it aims to answer is: Does the combination of these 2 modalities have the diagnostic accuracy similar to the gold standard test which is High Resolution Computed Tomography (HRCT) of the Lungs? Does this combination have the potential to become a validated screening tool? Participants will be in 2 groups: the RA group and the SSc group, each will have the diagnostic combination and a reference HRCT for comparison of results.

Interstitial lung disease (ILD) represents one of the most severe extra-articular and systemic manifestations of Rheumatoid Arthritis (RA) and Systemic Sclerosis (SSc). ILD significantly increases morbidity and remains a leading cause of mortality in both disease entities. Accumulating evidence demonstrates a high prevalence of subclinical interstitial lung disease, occurring in up to 33% of patients with rheumatoid arthritis and 50% of patients with systemic sclerosis. Therefore, Early detection during this subclinical window is paramount to initiate timely immunomodulatory or antifibrotic therapies before irreversible fibrotic replacement occurs. Although high-resolution computed tomography (HRCT) of the chest remains the gold standard for diagnosing interstitial lung disease, its high cost and associated radiation exposure restrict its utility as a routine screening tool for all patients, particularly in resource-limited settings. Consequently, there is a clinical demand for a validated, non-invasive, radiation-free, and cost-effective triage tool to screen populations at risk and identify those who genuinely require diagnostic HRCT evaluation. Growth Differentiation Factor-15 (GDF-15), a stress-responsive cytokine belonging to the Transforming Growth Factor-beta (TGF-β) superfamily, has emerged as a novel systemic biomarker reflective of cellular stress, inflammation, and fibrogenesis . GDF-15 is significantly elevated in active systemic autoimmune conditions such as Behcet disease, Inflammatory bowel disease and Sjogren's disease . Importantly, GDF-15 is overexpressed in pulmonary epithelial cells during active fibrogenesis and serves as a key circulating biomarker in idiopathic pulmonary fibrosis as well as connective tissue disease-associated ILD and pulmonary hypertension. As a cellular stress cytokine, serum GDF-15 reflects the distinct pathogenetic mechanisms driving ILD in each condition: RA-ILD: Mucosal citrullination and anti-CCP immune complex deposition 2022induce alveolar epithelial injury and inflammatory cytokine release. Here, elevated GDF-15 primarily reflects acute epithelial stress and immune-mediated inflammatory intensity. SSc-ILD: Microvascular damage and endothelial apoptosis trigger TGF-β signaling and myofibroblast expansion. Here, GDF-15 acts downstream of TGF-β, reflecting chronic endothelial ischemia and fibrogenesis. Concurrently, point-of-care Lung Ultrasound (LUS) has revolutionized bedside assessment in rheumatology. LUS detects interstitial pulmonary changes-specifically B-lines and pleural line irregularities-with exceptional sensitivity. Recent evidence highlights that LUS achieves remarkable diagnostic accuracy compared to HRCT in both RA-ILD and SSc-ILD. While GDF-15 reflects early molecular and cellular fibrotic activity and LUS identifies early structural lung affection, whether combining these two non-invasive modalities yields superior diagnostic accuracy for subclinical ILD screening compared to either modality alone remains unexplored. Combining a molecular circulating marker with a physical point-of-care imaging tool could establish a robust triage model for outpatient rheumatology clinics. Therefore, this is a diagnostic accuracy study to determine the outcomes of this combination.