Serum creatine phosphokinase activity in asthma.

Serum creatine phosphokinase activity was measured in 2 groups of asthmatics. The first group consisted of 12 asthmatics followed as outpatients for periods of up to 16 months. Serum creatine phosphokinase activity increased in 8 patients and correlated with the severity of subjective symptoms and objective measurement of airway obstruction, as represented by the forced expiratory volume in 1 second. In the second group, consisting of 5 asthmatic patients studied during hospitalization for acute exacerbations of asthma, serum creatine phosphokinase activity was increased on admission in all the patients and decreased as symptoms and airway obstruction improved and alveolar ventilation decreased. Analysis of creatine phosphokinase isoenzymes showed the increase in every instance to be due entirely to skeletal muscle isoenzyme. The results of additional laboratory tests and further evaluation suggested that the increased serum creatine phosphokinase activity was not derived from the myocardium and was not related to parenteral therapy, specific drugs, hyperthermia, or hyperkalemia. The increase in serum creatine phosphokinase during exacerbations of asthma is probably derived from respiratory muscles, owing to the increased work of breathing.