Reliability of peak expiratory flow percentage compared to endoscopic grading in subglottic stenosis

OBJECTIVE: To determine the reliability of pulmonary function testing compared to endoscopic grading in the assessment of subglottic stenosis. METHODS: Consecutively treated patients with subglottic stenosis at a tertiary care specialty hospital from 2009 to 2019 were identified. Two fellowship‐trained laryngologists and two otolaryngologists blinded to clinical history reviewed laryngo tracheoscopic examinations and assessed the degree of stenosis using the Cotton‐Myer grading system (% stenosis). Nine full flow‐volume loops were performed at the time of each exam. RESULTS: The endoscopic images of 45 subjects were graded for degree of stenosis and the spirometry data were analyzed. The kappa values for Cotton‐Myer grade overall was 0.37, grade I was −0.103, grade II was 0.052, and grade III was 0.045. The overall intraclass correlation of the physician grading of estimated percent obstruction (% stenosis) was 0.712 (P < .01) whereas the overall intraclass correlation for PEF% was 0.96 (P < .01). Within each Cotton‐Myer grade, the intraclass correlation for % stenosis was 0.45 (P = .02) for grade I, 0.06 (P = .30) for grade II, and 0.16 (P = .03) for grade III. The intraclass correlation for PEF% for grade I was 0.97 (P < .01), grade II was 0.92 (P < .01), and grade III was 0.96 (P < .01). CONCLUSION: Cotton‐Myer grading and estimating percent obstruction (% stenosis) for adult subglottic stenosis showed poor reliability as an assessment tool compared to the excellent intraclass correlation seen with pulmonary function tests within each Cotton‐Myer grade subgroup. We recommend pulmonary function testing, specifically PEF% because it is a normalized value, for the assessment and management of subglottic stenosis. LEVEL OF EVIDENCE: 4.