Elevated substance P levels in nasal lavage fluids from patients with chronic nonproductive cough and increased cough sensitivity to inhaled capsaicin

The exact mechanism of a chronic nonproductive cough is sometimes unclear when patients who are without symptoms or signs indicating the major causes of chronic cough remain undiagnosed. We hypothesized that some neurochemical alterations in the sensory nerves in the cough reflex may occur in the upper airway of chronic nonproductive cough patients. We took nasal lavage fluid (NLF) specimens from 38 patients with a chronic nonproductive cough as the sole presenting symptom. All 38 had normal chest radiography, spirometry, and bronchial responsiveness. We likewise took NLF specimens from 14 healthy control subjects. We used a capsaicin cough provocation test to determine cough sensitivity and considered the value of C 5 (the lowest capsaicin concentration inducing 5 consecutive coughs) as an index of cough sensitivity. We measured levels of substance P of NLF specimens by using ELISA. In addition, we evaluated the clinical response of each patient after subsequent therapeutic trials with an antihistamine and decongestant for 2 weeks. By using capsaicin cough sensitivity as the basis for grouping the study subjects, we divided the patients into 2 groups: an increased cough sensitivity group (ICS, C 5