Sudden-Onset Platypnea-Orthodeoxia Syndrome in a Patient with Lung Adenocarcinoma and COVID-19 Without a Patent Foramen Ovale.

Background: Platypnea-orthodeoxia syndrome is a rare but important cause of positional hypoxemia, typically resulting from a right-to-left shunt that may be intracardiac or intrapulmonary in origin. Case report: We present the case of a 78-year-old woman with metastatic lung adenocarcinoma and recent mild coronavirus disease 2019 (COVID-19) who developed acute-onset platypnea-orthodeoxia syndrome during hospitalization. Diagnostic workup revealed intrapulmonary shunting in the absence of pulmonary embolism or significant parenchymal lung disease. High-resolution chest computed tomography scan showed hypervascular consolidations, while bubble contrast transthoracic echocardiography confirmed delayed appearance of microbubbles in the left heart, consistent with an intrapulmonary shunt. Conclusion: This case highlights the complex interplay between tumour-induced intrapulmonary vascular abnormalities and possible COVID-19-related endothelial dysfunction in the development of platypnea-orthodeoxia syndrome. It emphasizes the need for heightened clinical suspicion and a multimodal diagnostic approach in patients with unexplained positional hypoxemia, especially in the setting of malignancy or recent viral infections. Diagnostic confirmation relies on imaging and shunt detection techniques, and management should be guided by the patient's overall prognosis and goals of care. LEARNING POINTS: Platypnea-orthodeoxia syndrome should be considered in patients with unexplained positional hypoxemia and/or dyspnoea, especially in the context of malignancy or recent viral infection.Contrast-enhanced echocardiography is key to identifying right-to-left shunts and distinguishing between intracardiac and intrapulmonary causes.Pulmonary malignancies and coronavirus disease 2019 (COVID-19) can independently or synergistically contribute to the development of platypnea-orthodeoxia syndrome through vascular remodelling and angiogenesis.