Predictors of Pulmonary Embolism in Interstitial Lung Disease With Worsening Symptoms

Interstitial lung diseases (ILDs) comprise a heterogeneous group of diffuse parenchymal lung disorders characterized by inflammation and fibrosis, often leading to progressive respiratory failure. Patients with ILD carry a heightened risk of venous thromboembolism, specifically pulmonary embolism (PE), driven by chronic inflammation, endothelial dysfunction, hypoxemia, reduced mobility, and a systemic pro-thrombotic state. The development of PE in ILD patients is associated with prolonged hospitalization, increased morbidity, and poor survival outcomes.

Diagnosing PE in this specific population remains clinically challenging because the acute manifestations, such as worsening dyspnea and hypoxemia, closely mimic those of an acute ILD exacerbation. Furthermore, conventional clinical prediction models, such as the Wells and Revised Geneva scores, frequently exhibit limited diagnostic accuracy in this cohort because respiratory distress and baseline hypoxia are already common underlying features of ILD.

To address this diagnostic gap, this prospective observational study will evaluate patients with a confirmed diagnosis of ILD who present with an acute, unexplained worsening of respiratory symptoms and undergo Computed Tomography Pulmonary Angiography (CTPA).

Comprehensive clinical, laboratory, and radiological data will be systematically collected for all participants to identify independent predictors of PE. The study workflow includes:

• Clinical Scoring: Calculation of established pre-test probability and mortality risk scores, including the traditional and simplified Wells score, Revised Geneva score, Pulmonary Embolism Severity Index (PESI), and Simplified PESI (SPESI).
• Laboratory Assessment: Evaluation of novel inflammatory indices, including the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR). Additional laboratory profiling includes D-dimer, C-reactive protein (CRP), serum total protein, serum albumin, renal and liver function tests, and arterial blood gas analysis to calculate the A-a oxygen gradient.
• Radiological & Echocardiographic Evaluation: High-Resolution CT (HRCT) will be used to quantify ILD disease severity and extent via the Warrick Score. CTPA scans will be analyzed for embolus location, right ventricular (RV) diameter, RV/LV diameter ratio, and main pulmonary artery diameter. When available, transthoracic echocardiography will assess RV size and systolic function, TAPSE, fractional area change, McConnell sign, the 60/60 sign, and inferior vena cava collapsibility.

Through multivariable logistic regression and Receiver Operating Characteristic (ROC) curve analysis, the study will compare these parameters between patients with CTPA-confirmed PE and those with negative scans. The goal is to validate the predictive strength of these biomarkers and imaging parameters, supporting the development of a disease-specific diagnostic prediction model to enhance clinical decision-making for ILD patients.

Inclusion criteria

• Age ≥ 18 years
• Confirmed diagnosis of ILD based on multidisciplinary discussion and HRCT findings, with or without histopathological confirmation
• Acute unexplained worsening of dyspnea, hypoxemia, chest pain, syncope, or clinical suspicion of PE
• Undergoing CTPA as part of routine clinical management
• Provision of informed consent

Exclusion criteria

• Age < 18 years
• Pregnancy
• Previously diagnosed acute pulmonary embolism receiving anticoagulant therapy
• Active malignancy
• Known inherited or acquired thrombophilia
• Acute myocardial infarction or ischemic stroke within the previous month
• Major surgery or trauma within four weeks
• Severe renal impairment contraindicating contrast-enhanced CTPA