Clinical and laboratory features of chronic cough
Chronic cough is a common presenting symptom to both general practice and respiratory clinics and in up to 20% of patients, the cough remains unexplained after extensive investigation and treatment trials. In this thesis, we have shown that patients with idiopathic chronic cough are predominantly female, have an onset of cough in middle age and have a high prevalence of organ specific autoimmune disease, particularly hypothyroidism. We found that idiopathic chronic cough is associated with a bronchoalveolar lavage lymphocytosis and have suggested that this is due to homing of activated lymphocytes from the primary site of autoimmune inflammation to embryologically related structures such as the airways, analogous to the mechanism thought to be responsible for airway complications of inflammatory bowel disease. The concept that chronic inflammation of foregut structures can be associated with airway symptoms, inflammation and damage is also supported by our finding of a striking excess of cases of treated hypothyroidism amongst a predominantly elderly non-smoking female population with fixed airflow obstruction and a 2-3 fold excess of respiratory symptoms in a cohort of patients with autoimmune hypothyroidism and another with inflammatory bowel disease. We have also shown raised histamine concentrations in airway secretions of patients with idiopathic chronic cough, which suggests a possible mechanism whereby airway inflammation results in cough and raises the possibility that antihistamines may have a therapeutic role in idiopathic chronic cough. Finally, recognising the major impact of chronic cough on health status and the paucity of objective measures available for the assessment of cough, we developed the Leicester Cough Questionnaire, which is a 19-item cough specific quality of life questionnaire.