Objective characterisation of difficult asthma in the WATCH study

Background: Better understanding of difficult asthma phenotypes allows personalisation of therapy regimes targeted to individual disease. Aims: Our aim was to phenotypically characterise difficult asthma in the clinic. Methods: We collected clinical data to objectively characterise enrolled patients (n=380) from a tertiary difficult asthma clinic (Southampton; UK) into the Wessex AsThma CoHort (WATCH). Results: Subjects were aged 17-85 years (median age=51). Median age at asthma diagnosis was 18 years. Atopy (defined by positive skin test) was seen in 68.2% (n=315), with fungal sensitivity in 10.2 % (n=294). Mean total IgE was 305.2 (95%CI 229.4-381.0, n=345). Peripheral blood eosinophilia of ≥0.3 occurred in 34.5% of patients (n=355). 19.6% of patients had a FeNO ≥40ppb (n=285). Mean post bronchodilator (BD) FEV1 (n=286) was 72.3% predicted (95%CI 76.4-81.5), with FEV1/FVC of 67.6% (95%CI 65.9-69.3). Post BD FEF 25-75 was 51.0% predicted (95%CI 47.1-54.89, n=256). Gas transfer was preserved, with a mean KCO of 101.3% (95%CI 98.8-103.7, n= 203). HRCT (n=239) findings included bronchial wall thickening (45.6%), bronchiectasis (22.2)%, air trapping (17.2%), mucous plugging (10.0%), emphysema (9.2%), and bronchial dilatation (8.4%). CT chest was normal in 15.7%. Rhinitis was present in 72.7% (n=320), with CT sinus results for 51 patients, all of which were abnormal, with mucosal thickening in 68.6%, abnormal nasal turbinates in 56.9%, nasal septal deviation in 49.0%, sinus opacification in 41.2% and nasal polyps in 29.4%. Conclusion: These results suggest that many patients possess disease characteristics that can guide management strategies, with a substantial proportion potentially amenable to biological treatments.