Patients with difficult asthma suffer chronic moderate to severe persistent asthma symptoms despite high doses of inhaled and oral corticosteroid therapy. These patients suffer a high level of treatment and disease related morbidity but little is known about the degree of airway inflammation in these patients.

Fifty two patients were examined to assess levels of exhaled nitric oxide (NO) as a surrogate marker of inflammatory activity in this condition. From this group, 26 patients were defined with severe symptoms and current physiological evidence of reversible airway obstruction requiring high dose inhaled (⩾2000 μg beclomethasone dipropionate (BDP) equivalent) or oral steroid therapy to maintain disease control.

Exhaled NO levels were higher in subjects with difficult asthma (mean 13.9 ppb, 95% CI 9.3 to 18.5) than in normal controls (7.4 ppb, 95% CI 6.9 to 7.8; p<0.002), but lower than levels in steroid naive mild asthmatics (36.9 ppb, 95% CI 34.6 to 39.3; p<0.001). Prednisolone treated patients had higher exhaled NO levels than patients only requiring inhaled corticosteroids (17.5 ppb, 95% CI 11.1 to 24.0 versus 7.2 ppb, 95% CI 4.6 to 9.8; p = 0.016), suggesting greater disease severity in this group. Non-compliance with prednisolone treatment was observed in 20% of patients but this did not explain the difference between the treatment groups. Exhaled NO levels were closely correlated with symptom frequency (p = 0.03) and with rescue β agonist use (p<0.002), but they did not correlate with lung function.

Exhaled NO may serve as a useful complement to lung function and symptomatology in the assessment of patients with chronic severe asthma, and in the control and rationalisation of steroid therapy in these patients.