Introduction Up to 80% of patients with sarcoidosis report a chronic cough. The aim of this study was to investigate whether heightened cough reflex sensitivity (CRS) is an important mechanism and to establish if factors such as gender, serum ACE level and radiographic stage influence sensitivity thresholds.
Methods Twenty-four patients with sarcoidosis (mean (SEM) age 49 (2) years, 63% female) were recruited from a specialist clinic and underwent assessment of CRS by a single-breath inhalation capsaicin cough challenge test to determine the concentration causing 5 or more coughs (C5). Anthropometric data, spirometry, serum ACE levels and radiographic stage were recorded. The effects of gender, age, ethnicity, radiographic stage and serum ACE levels on cough reflex sensitivity were investigated. CRS data of 134 healthy subjects from a previous study were used for comparison (Prudon B et al, Chest 2005;127:550).
Results CRS was heightened in patients with sarcoidosis compared to healthy subjects (geometric mean (logSD) C5 13.5 (0.5) vs 158.5 (0.6) μmol/l, p<0.001). Female patients had a more sensitive cough reflex compared to males (geometric mean (logSD) C5 8.1 (0.5) vs 31.8 (0.5) μmol/l, p=0.007). Seven patients did not complain of cough; there was no difference in CRS compared to patients who reported cough (p=0.68). There was no difference in CRS between patients of Afro-Caribbean origin compared to non-Afro-Caribbean patients (geometric mean (logSD) C5 10.1 (0.5) vs 24.3 (0.6) μmol/l, p=0.09). Serum ACE levels correlated significantly with logC5 (r=0.74, p<0.001), with lower ACE levels being associated with a more sensitive cough reflex. There was no relationship between logC5 and age (r=−0.40, p=0.054) or radiographic stage (p=0.83).
Conclusions Patients with sarcoidosis have a heightened CRS. This was increased to a greater degree in females, but age or radiographic stage had no effect. We report for the first time a link between serum ACE levels and cough reflex sensitivity, and hypothesise that low concentrations of serum ACE lead to increased airway tussigenic mediators such as bradykinin. Further studies should investigate whether cough receptors such as TRPV1 are upregulated in sarcoidosis.
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