The role of the methacholine inhalation challenge in adult patients presenting with chronic cough.

ABSTRACT

One hundred and twenty two patients who were presenting with chronic persistent cough for more than 3-4 weeks were studied. Using anatomical and stepwise approach, we could identify the cause of chronic cough in 96% of the patients. The most common causes were due to postnasal drip syndrome (PND) (45%) and bronchial asthma (26%). We also demonstrated the important role of methacholine inhalation challenge in the diagnostic work up. The procedure could identify the patients who had bronchial hyperresponsiveness (BHR) in 52% of the cases. The severity degree of the BHR was classified into three levels. Mild or nonspecific BHR was defined as PC20 16-25 mg/ml. This could be found in many diseases such as PND and bronchiectasis. Moderate degree of BHR (PC20 8-16 mg/ml) was found in patients with PND and asthma. PC20 of less than 8 mg/ml was considered to be the most severe degree and it seemed to be specific for the diagnosis of asthma (positive predictive value 100%). Other condition that caused chronic cough were drug-induced, especially angiotensin-converting enzyme inhibitors, gastroesophageal reflux disease (GERD), idiopathic pulmonary fibrosis, subgottic cancer and idiopathic cough. These conditions may require invasive diagnostic work up, such as fiberoptic bronchoscopy and tissue biopsy. The treatment of chronic cough was according to the etiology. Thus, the patients presenting with chronic cough should be investigated to identify the cause, and it was not just only the administration of cough suppressant drugs in these patients.