Utility of microRNA analysis in exhaled breath condensate of sarcoidosis and mediastinal tuberculosis patients: a pilot study.

Background: Sarcoidosis and tuberculosis (TB) are the two most common causes of granulomatous mediastinal lymphadenopathy. These often exhibit overlapping clinical and radiological characteristics, rendering accurate diagnosis difficult. MicroRNA (miRNA) analysis is increasingly utilised as a potential biomarker for various diseases. Exhaled breath condensate (EBC) is a noninvasive technique for biomarker evaluation in different respiratory conditions. We attempted to identify differentially expressed miRNAs in the EBC of sarcoidosis and mediastinal TB patients.

Methods: EBC was obtained from subjects with a definitive diagnosis of sarcoidosis and mediastinal TB. EBC was also obtained from age- and sex-matched control subjects. From EBC, miRNA isolation, cDNA preparation and qPCR array were performed. Differentially expressed miRNAs were shortlisted. Further validation was conducted in the EBC of a new subset.

Results: Subjects with a definitive diagnosis of sarcoidosis (50) and TB (50), and control subjects (50) were included. qPCR array from EBC (20 subjects from each group) shortlisted eight differentially expressed miRNAs (miR-126, miR-132, miR-139-3p, miR-139-5p, miR-181c, miR-454, miR-512-3p and miR-362-5p). In the validation set (EBC of 30 subjects from each group), miR-126 and miR-132 were differentially expressed significantly. The miR-126 and miR-132 expression ratio could differentiate sarcoidosis from mediastinal TB with an AUC of 0.618 (82% specificity and 41% sensitivity).

Conclusion: While EBC miRNA expression is significantly and differently altered in sarcoidosis and mediastinal TB, a simple ratiometric approach failed to provide clinically useful signatures for differentiating between the two in patients with mediastinal lymphadenopathy.