Significance of the pulmonary function test for the diagnosis of subglottic stenosis: a systematic review

Objective: Subglottic stenosis is diagnosed on the basis of clinical presentation and flexible laryngoscopy findings and confirmed by direct laryngobronchoscopy. Other adjunct diagnostic methods have been proposed, including the pulmonary function test. This study aimed to systematically review the existing literature on the parameters of the pulmonary function test in patients with subglottic stenosis in order to provide clinicians with evidence-based information about its diagnostic utility. Methods: We searched the Medline, PubMed, Scopus, Cochrane Library, Cumulative Index to Nursing and Allied Health Literature, and ProQuest dissertation databases for prospective or retrospective studies of adults diagnosed with subglottic stenosis, who underwent the pulmonary function test preoperatively. The data were collected by 2 independent authors who also assessed the quality of each study. Results: Of the 479 studies identified, only 1 article met our inclusion criteria; the study included 42 patients with 251 pulmonary function test measurements (preoperative, n=45; postoperative, n=206). The mean peak expiratory flow and expiratory disproportion index before intervention were 3.19 L/s and 73.8, respectively, and those after intervention were 5.49 L/s and 44.9, respectively. Conclusion: Available evidence suggests that the pulmonary function test alone, without airway visualization, is an unreliable method for diagnosing subglottic stenosis. However, it may be a useful adjunctive diagnostic tool to indicate subglottic stenosis, with an expiratory disproportion index value of 54 and a peak expiratory flow value of 4.4 L/s as presumptive cut-off diagnostic values. The pulmonary function test may also be useful postoperatively to monitor disease progress during follow-up.