To immunosuppress or not: Behcet's syndrome presenting as an eosinophilic pleural effusion.

Etiologic diagnosis of an eosinophilic pleural effusion (EPE) presents a diagnostic challenge when intrapleural air and blood have been ruled out as its proximate causes. Among the causes of EPE, those that require immunosuppression for the underlying disease include connective tissue diseases, sarcoidosis, vasculitis, and eosinophilic pneumonia. We present a case of clinically suspected Behcet's syndrome based on a 10-year history of recurrent multiple oral ulcers and human leukocyte antigen-B51 positivity who presented with only an EPE. Computed tomography pulmonary angiogram ruled out central thoracic vein thrombosis but was inconclusive in ruling out a subsegmental pulmonary embolism. The patient declined immunosuppressants and while on follow-up developed bilateral extensive acute lower limb deep venous thrombosis and pulmonary embolism. Upper infrarenal inferior vena cava demonstrated chronic thrombosis suggestive of its antecedent role in pulmonary embolism-related EPE during the first instance. Behcet's syndrome-related EPE can be associated with venous thromboembolism, and immunosuppressive therapy prevents the subsequent thrombotic episodes.