Left pleural effusion and fever of unknown origin--a clue to thoracic arterial pathology.

The subset of patients who have both fever of unknown origin (FUO) and a nondiagnostic pleural effusion on presentation has not been previously investigated. A retrospective search of all patients classified as 'classic' FUO one week after admission to a department of general internal medicine identified 71 patients over 15 years. Seven were found to have associated pleural effusion(s) on admission (9.8%). In three patients thoracic large vessel pathology was diagnosed (chronic aortic dissection, giant cell arteritis and Takayasu arteritis). In these patients, the pleural effusion was predominantly left-sided, small to moderate in amount and nondiagnostic on thoracentesis. The effusions resolved spontaneously or with appropriate treatment. Thus, in patients with prolonged fever and systemic symptoms, a 'bland' left-sided pleural effusion may be a diagnostic clue to underlying inflammation of large thoracic arteries. Pleural irritation due to its anatomical proximity to the large arteries on the left side of the thorax may underlie the pathogenesis. Recognition of this sign may lead to a more timely diagnosis of occult thoracic large vessel pathology.