Utility of the expiratory disproportion index in early detection of idiopathic subglottic stenosis masked by asthma

Idiopathic subglottic stenosis (iSGS) is a rare fibrotic condition causing fixed extrathoracic airway obstruction, predominantly affecting postmenopausal women. The expiratory disproportion index (EDI), calculated as forced expiratory volume in one second (FEV1) (mL)/peak expiratory flow (PEF) (L/min), can help differentiate fixed extrathoracic obstruction from obstructive lung diseases. Here we present the case of a 62-year-old woman with mild intermittent asthma who presented with progressive dyspnea and dry cough following COVID-19 infection. Spirometry revealed expiratory flattening with preserved FEV1/forced vital capacity, markedly reduced PEF, and inadequate inspiratory curves. Laryngotracheoscopy confirmed iSGS, and surgical excision with balloon dilation resolved the stenosis. Routine EDI calculation in pulmonary function testing may facilitate earlier iSGS detection and reduce diagnostic delay in patients with refractory asthma-like symptoms.