Estimate Precision
We have been unable to find a case report of an AD presenting as ABHL, and compendia of the clinical and radiographic features of TB and lymphoma contain no examples. Estimates of the proportion of ADs that present as ABHLs were derived in each instance by assuming a value high in the range consistent with available data, thus favoring mediastinoscopy. These estimates are necessarily imprecise.
Robustness
If, by a combination of overestimation of IABHL_S1S and underestimation of IAbhl-ad> we overestimated the incidence ratio by 100%, 16,000 patients with ABHL would be required to undergo mediastinoscopy to identify 18 patients with an AD at a cost of $50 to $100 million; 99.89% would be found to have sarcoidosis; 200 would require hospitalization at a cost in excess of $500,000; 100 would experience major morbidity; and the benefit for persons diagnosed as having lymphoma or TB would be minimal and likely offset by the aggregate procedural mortality- Iabhl ad would have to be 1,000-fold higher than our estimates to reduce the cost of case identification to $10,000 to $20,000 and nullify our conclusion.
Angiotensin I-Converting Enzyme
Fanburg et al reported that the enzyme level was 2 SDs above the mean value in normal subjects in 48% of patients with confirmed sarcoidosis and in 10% of patients with TB or lymphoma (90% specificity). A positive test would therefore increase the posterior probability of sarcoidosis by 0.03 to 99.98%. In a cohort of 1,000 patients with ABHL, 480 patients would have a true-positive test, 519 would be incorrectly identified as not having SIS (false-negative), and 1 patient with an AD would be correctly identified (true-negative). Mediastinoscopy would be required in 519 patients with false-negative tests to identify one AD at a cost of $1.5 to $3 million and attendant morbidity. Tracheobronchoscopy
Transbronchial Lung Biopsy
In experienced hands, noncaseating granulomas are obtained in 66% of SIS patients by this means. Bleeding, sometimes fatal, and pneumothorax are its most frequent complications. Because of its far greater sensitivity and specificity, mediastinoscopy is preferred when the intent is to exclude mediastinal TB and lymphoma, both of which may be accompanied by noncaseating granuloma in the lung. Though its cost (approximately $2,000) is less than mediastinoscopy, patients with a nondiagnostic biopsy specimen will require a second procedure.