Capsaicin induced cough in cryptogenic fibrosing alveolitis

Background-Cough is a common and troublesome symptom in cryptogenic fibrosi ng alveolitis (CFA) but the mechanisms responsible are not known. The cough threshold to inhaled capsaicin is increased in asthma and chronic obstruct ive pulmonary disease (COPD) where lung volumes are increased, but the rela tionship between cough response and symptom intensity has not been studied in CFA where lung volumes are reduced. Methods-Capsaicin challenge tests were performed on 15 subjects with proven CFA and 96 healthy controls. Symptoms, as assessed by daily diary card cou gh score and by visual analogue scale (VAS), were related to the capsaicin sensitivity (C5) and compared with lung volumes. Volume restriction was pro duced in a group of 12 normal healthy subjects by a plastic shell tightly s trapped to the chest wall. Capsaicin challenge tests were performed in thes e subjects, both strapped and unstrapped, to determine whether volume restr iction altered the cough reflex. Results-The median C5 response in normal subjects was more than 500 muM com pared with 15.6 muM in those with CFA (p<0.001). The C5 response of the CFA patients was not related to symptoms of cough (whether measured by diary c ard or by VAS), nor was it related to percentage predicted total lung capac ity (TLC) or forced vital capacity (FVC). Volume restriction of normal subj ects with chest strapping successfully restricted lung volumes to levels si milar to that of the CFA patients but did not change the sensitivity to cap saicin. Conclusions-The cough reflex measured using capsaicin is markedly increased in patients with CFA. This increase is not the result of alterations in th e deposition of inhaled particles of capsaicin brought about by volume rest riction. It could be related to reduced lung compliance leading to sensitis ation of rapidly adapting receptors, other mechanical changes, or to destru ction of pulmonary C fibres secondary to interstitial inflammation. The cap saicin test may be a useful method of objectively monitoring cough propensi ty in CFA.