Inhaled and systemic corticosteroid therapies: Do they contribute to inspiratory muscle weakness in asthma?

Background: Patients with asthma incur the risk of steroid-induced myopathy, which is a well-known side effect of treatment with corticosteroids. However, the adverse effect of long-term steroid treatment on respiratory muscle function remains controversial. Objective: We aimed to evaluate the effects of long-term moderate dose of systemic corticosteroids and high-dose inhaled beclomethasone on maximal inspiratory and expiratory pressures (Plmax and PEmax, respectively) in two groups of asthmatic patients exhibiting comparable levels of hyperinflation. Methods: Twelve steroid-dependent asthmatic patients requiring 10-20 mg/day of prednisone-equivalent corticosteroids for an average of 9.83 +/- (SD) 9.86 years; 14 subjects with moderate to severe asthma who have used inhaled beclomethasone for at least 1 year at a daily dose higher than 1,000 mu g and 15 healthy controls were included to the study. Results: No significant difference in pulmonary function tests and arterial blood gases appeared between two asthmatic groups with different treatment modalities. Plmax as an absolute value was significantly lower in steroid-dependent asthmatics than in patients treated with inhaled beclomethasone and controls (p < 0.01). %Plmax was also lower in steroid-dependent asthmatics than in control groups (p < 0.01). A significant correlation was found between %Plmax and hyperinflation assessed by %RV, %FRC, %FRC/TLC (p < 0.05) in all asthmatic patients. Conclusions: We believe that hyperinflation plays a major role in inspiratory muscle dysfunction in asthma, but the finding of significantly decreased Plmax values in steroid-dependent asthmatics when compared with patients on high-dose inhaled beclomethasone with a comparable level of hyperinflation points to a deleterious effect of long-term, moderate-dose systemic corticosteroid but not high-dose beclomethasone on inspiratory muscle function in asthmatics.