Transient Bilateral Atrial Thrombi in a Patient With Multiple Sclerosis and Massive Pulmonary Embolism: A Case Report and Review of the Literature.

Pulmonary embolism (PE) can present with complex and atypical features that challenge diagnosis and management, particularly when coexisting with intracardiac thrombi and neurological symptoms. We report a case of a 67-year-old woman with multiple sclerosis (MS) who presented with bilateral PE, bi-atrial thrombi, and a subsequent embolic stroke. Despite initial imaging suggesting a possible atrial septal defect (ASD) as the route for paradoxical embolism, both transthoracic echocardiography and cardiac magnetic resonance imaging failed to confirm any intracardiac shunt. The case underscores the diagnostic difficulties in differentiating between stroke and MS relapse, as well as limitations of imaging modalities in transient thrombotic or shunt-related phenomena. The patient was managed with therapeutic anticoagulation, which resulted in thrombus resolution and clinical improvement. This case highlights the need for high clinical suspicion and multidisciplinary evaluation in patients with overlapping cardiovascular and neurological presentations, especially in the setting of chronic inflammatory diseases such as MS.