Thrombus Size Matters: A Risk Assessment Model for Predicting Pulmonary Embolism in Isolated Distal Deep Vein Thrombosis.

Rationale And Objectives: Isolated distal deep vein thrombosis (IDDVT) is an insidious condition that can lead to pulmonary embolism (PE). This study aimed to develop and validate a risk assessment model based on thrombus size and patient characteristics to predict the risk of concomitant PE in IDDVT patients.

Methods: A retrospective analysis of 494 IDDVT patients was conducted, divided into a derivation cohort (n=398) and a validation cohort (n=96). Patients were categorized into PE and non-PE groups based on computed tomography pulmonary angiography (CTPA) results. Clinical, laboratory, and ultrasound data-including thrombus diameter and length-were collected. Independent risk factors for PE were identified using multivariate logistic regression, and a nomogram was developed. Model performance was evaluated through internal and external validation. Additionally, the study compared the diagnostic efficacy of the thrombus size threshold for IDDVT complicating PE with the threshold recommended by the guidelines.

Results: Independent predictors of PE in IDDVT patients included thrombus diameter ≥5mm, thrombus length ≥30mm, pulmonary artery pressure >40 mmHg, elevated D-dimer, male sex, and recent surgical history. The model achieved a C-statistic of 0.78 and a Brier score of 0.19. Internal validation confirmed robust discriminative power (C-statistic 0.78, 95% CI 0.73-0.82), while external validation yielded a C-statistic of 0.71 and a Brier score of 0.22. DCA demonstrated a net benefit within a threshold risk range of 12-83%. Compared to previous thrombus size thresholds (7 mm diameter and 50 mm length), the new thresholds (5 mm diameter and 30 mm length) improved discrimination by 11% (95% CI 0.08-0.15, p<0.001) and net reclassification by 52% (95% CI 0.33-0.71, p<0.001).

Conclusion: This retrospective study developed a validated risk assessment model using thrombus size indices of ≥5 mm in diameter and ≥30mm in length, alongside clinical factors, to effectively evaluate the risk of concomitant PE in IDDVT patients. This model may offer a valuable tool for individualized risk stratification and clinical decision-making.