Cough variant and cough-predominant asthma are major causes of persistent cough: a multicenter study in Japan.

Objective: Persistent cough is a frequent cause of doctor and hospital visits, and its incidence may be increasing. However, diagnosis of the cause of cough remains difficult. Because different causes of cough have different treatments, accurate diagnosis of the cause of cough is critical. To gain a better understanding of the causes of cough in Japan, we performed a multicenter epidemiological study of Japanese patients.

Methods: The study involved seven institutions in five different areas of Japan, and was conducted over 1 year from March 2009. Patients aged ≥16 years attending the participating centers for the first time complaining of cough persisting for ≥3 weeks were eligible. Patients with chest X-ray abnormalities responsible for cough, fever or blood-stained sputum were excluded, while those with wheeze or shortness of breath were included. Frequency and severity of cough were assessed using questionnaires, and laboratory tests were performed to enable differential diagnoses.

Results: Among the 313 patients evaluated, mean duration of cough symptoms was 192.1 ± 558.4 days. Cough variant asthma (CVA) was the most common cause of prolonged/chronic cough (42.2%), followed by cough-predominant asthma (CPA) (28.4%), atopic cough (7.3%) and chronic obstructive pulmonary disease (6.7%). Patients with an unclear diagnosis were treated with tulobuterol, a transdermal β2-agonist preparation, for 1-2 weeks. Transdermal tulobuterol improved assessments of cough in patients with CVA or CPA, enabling rapid diagnosis of these diseases.

Conclusions: These findings show that CVA and CPA are the main causes of cough persisting for ≥3 weeks.