Platypnea-orthodeoxia syndrome in a patient with poor activity of daily living: Struggling with a definitive diagnosis.

A 73-year-old female patient was diagnosed with lumbar spinal stenosis by an orthopedic surgeon. During admission for further evaluation, she was found to have hypoxemia. Contrast-enhanced computed tomography revealed a 43-mm ascending aortic aneurysm, but there were no signs of pulmonary embolism, and no abnormalities were detected in the lung fields. Upon initiating rehabilitation in the standing position, respiratory distress and hypoxemia worsened. Careful observation revealed that hypoxemia worsened in the seated position but normalized while lying down. We considered the possibility of platypnea-orthodeoxia syndrome (POS), in which hypoxemia worsens in the seated position. Transesophageal echocardiography revealed that a patent foramen ovale (PFO), which was hardly noticeable while lying down, worsened in the seated position. A pulmonary perfusion scan showed a 27 % right-to-left shunt. Cardiac catheterization confirmed the presence of right-to-left shunting during right atrial injection. Consequently, it was diagnosed that the ascending aortic aneurysm aggravated the PFO in the seated position, leading to POS. The PFO was unsuitable for transcatheter treatment. Consequently, the patient underwent direct closure surgery in the cardiac surgery department. Postoperatively, the patient's hypoxemia and respiratory distress in the seated position improved, and subsequent progress has been favorable. Learning objective: Diagnosing platypnea-orthodeoxia syndrome in patients with poor activities of daily living (ADL) is challenging. Careful observation of the percutaneous oxygen saturation in both supine and seated positions is crucial, and a transesophageal echocardiogram in the supine and seated positions is inevitable. Lung perfusion scintigraphy is often used to evaluate the cause of hypoxemia; however, whole-body scans are important for detecting the presence and number of right-left shunts. This case report highlights the pitfalls of diagnosis in patients with poor ADL.