Abstract Title A Clot Conundrum: Reassessing Interstitial Lung Disease as Pulmonary Embolisms with Aubagio Use Background Interstitial lung disease and pulmonary embolism are rare side effects reported post teriflunomide use. Based on a trial evaluating the potential long-term effects of teriflunomide, reports of such adverse reactions have emerged from the TOWER extension study1 as well as several case studies2,3,4 . There are case reports of suspected pneumonia with a CT angiogram performed upon lack of clinical improvement, with pulmonary embolisms found there after. Here we report a case of suspected interstitial lung disease in the setting of teriflunomide use and upon further investigation, multiple pulmonary embolisms were discovered. Case Presentation A 46 year old female with a past medical history of multiple sclerosis, who was started on Teriflunomide four years prior, presented with progressive dyspnea, with persistent deoxygenation for one year based on an Apple watch monitoring device. The patient had several CT chest without contrast studies that were suggestive of interstitial lung pneumonitis prompting discontinuation of Teriflunomide and initiation of steroids. When the patient had no clinical improvement, a CT Angiogram with contrast later revealed extensive pulmonary artery emboli at multiple levels. Transthoracic echocardiogram revealed significant right heart strain. She was then started on a heparin drip and underwent a bilateral pulmonary endarterectomy. Following this, the patient was started on oral anticoagulation and was continued on steroids. Discussion There have been a few reported cases of either interstitial lung disease and pulmonary embolism linked to Aubagio use in multiple sclerosis patients. In our case, a patient presumed to have interstitial lung disease was later diagnosed with multiple pulmonary embolisms. A more comprehensive evaluation of potential side effects could have resulted in earlier, more effective treatment. Thus, we caution against solely attributing symptoms to one side effect and recommend early consideration of multifactorial and broader adverse effects of Aubagio.