“Airway hyperresponsiveness in postnasal drip syndrome: assessment using methacholine challenge – a prospective cross-sectional study”

Abstract

Background
Airway hyperresponsiveness refers to exaggerated bronchoconstriction in response to stimuli that elicit minimal effects in healthy individuals. Postnasal drip syndrome, also termed upper airway cough syndrome, arises from excessive nasopharyngeal secretions draining into the pharynx. This study evaluated the prevalence and degree of bronchial hyperresponsiveness in patients with postnasal drip syndrome using methacholine bronchial provocation testing.


Methods
In this cross-sectional study, a total of 79 participants with confirmed postnasal drip syndrome were recruited consecutively from the outpatient clinics of the Pulmonary and ENT Departments. Diagnosis of PNDS was established by rigid nasal endoscopy performed at the ENT clinic. Consecutive sampling was used, and participants were enrolled until the target sample size of 79 was achieved. Patients with lower airway disease were excluded. All participants underwent methacholine bronchoprovocation testing. Airway hyperresponsiveness was defined as ≥20% decline in FEV1, with severity graded by the provocative concentration causing a 20% fall (PC20). Patients were subsequently stratified into BPT-positive and BPT-negative groups based on the test results.


Results
Mean age 37.6 years, 64.6% female, 49.4% had a positive methacholine BPT. Chronic sinusitis (54.4%) and GERD (49.4%) were the most common etiologies. GERD, chronic sinusitis, and allergic rhinitis were significantly more prevalent in BPT-positive patients. Post-bronchodilator FEV₁ was lower [2.36 vs 3.19 L, p < 0.001] and median percentage fall in FEV₁ was higher [23.0% vs 5.0%, p < 0.001] in the BPT-positive group. A dose-response relationship was observed between AHR severity and bronchoprovocation parameters. On multivariable analysis, chronic sinusitis was the only independent predictor of BPT positivity (aOR 7.98, p = 0.002). GERD was significantly associated with lower PC₂₀ values [0.70 vs 6.10 mg/mL, p < 0.001], indicating greater AHR. No correlation was found between percentage fall in FEV₁ and PC₂₀ (r = -0.172, p = 0.295).


Conclusions
Postnasal drip syndrome is associated with airway hyperresponsiveness regardless of overt lower airway disease, with chronic sinusitis and GERD as key associated etiologies. Chronic sinusitis independently predicted BPT positivity, while GERD correlated with greater AHR severity. These findings support screening for AHR and aggressive management of underlying PNDS causes.