Exercise capacity, peripheral muscle dysfunction and genotype in adults with cystic fibrosis

Introduction: In an own previous study, we observed that many adult patients with cystic fibrosis (CF) and with normal pulmonary function have a decrease in their exercise capacity (EC) and some patients with moderate or severe airflow obstruction have normal EC. Objective: To determine the cause of reduced EC in adult patients with CF and their relation with lung function and genotype. Methods: We included 39 patients over 16 years of age with a confirmed diagnosis of CF. A respiratory function test (RFT), exercise test, muscle biopsy, with histologic and respiratory chain study, and electromyography (EMG) will be performed. Results: EC is decreased in 15/25 (60%) patients with milder genotypes (I-II/III, I-II/IV and I-II-V) and in 8/14 (57%) with more severe genotypes (I -II/I-II). The primary cause is a state of deconditioning and/or a peripheral muscle dysfunction in 9/15 (60%) patients with milder genotypes and in 4/8 (50%) with severe genotypes. All the respiratory chain studies and EMG were normal. 11 (28%) muscle samples, unrelated to the genotype, showed nonspecific findings that suggest a neuropathic pathologic basis. In patients with moderate or severe airflow obstruction (23), no significant differences in RFT were observed between patients with milder (12) and severe genotypes (11). Conclusions: Patients with CF have a decrease in their EC. In most cases, the primary cause is a state of deconditioning and/or a peripheral muscle dysfunction. But we do not find significant alterations in the histologic and respiratory chain study, regardless of genotype. More studies will be needed to clarify the cause of peripheral muscle dysfunction observed in these patients.