Dados do Trabalho

Título

Profile of respiratory chain enzyme activity in patients with exercise intolerance and mild changes at muscle biopsy

Resumo

Introduction: Exercise intolerance is a nonspecific term used to describe disproportionate fatigue, myalgia and/or cramping as a consequence of muscular exertion. Although it is a common complaint, a specific etiologic diagnosis is rarely achieved, even after comprehensive investigation.
Objective: In the present study we aim to define the profile of respiratory chain enzyme activity in skeletal muscle of patients with exercise intolerance and mild and nonspecific changes at muscle biopsy.
Patients and Methods: One hundred and three adult patients with long lasting
unexplained exercise intolerance were included in the study. They were followed at the outpatient clinic of our University Hospital and were subjected to muscle biopsy in the course of diagnostic investigation. Inclusion criteria: 18 years old or above; chronic (2 years or more) myalgia and/or fatigue in relation to exercise; non-specific findings in the muscle biopsy. Exclusion criteria: insufficient muscle sample size for enzyme assays. Respiratory chain activities of complexes I, II, III, II+III and IV were measured in whole muscle homogenates. Citrate synthase activity was measured to estimate the mitochondrial mass, which was used to correct enzyme activity.
Results: Activity of respiratory chain enzymes was unremarkable in 70% of patients. However, 16% of patients presented a complex I deficiency (mean 0.38 and SD 0.29 micromol/min/g tissue; when corrected for citrate synthase activity). Another 9% of patients presented isolated deficiency of complexes II (mean 0.48 and SD 0.34), III (mean 0.72 and SD 0.25) or IV (mean 1.12 and SD 0.3). In 5% of patients, there was a combined deficiency of complexes I, III and IV.
Conclusion: Although skeletal muscle biopsy with routine histochemical studies frequently show mild and nonspecific changes in patients with exercise intolerance, respiratory chain enzyme assays may contribute to a better understanding of the pathophysiology of exercise intolerance in a significant portion of those patients.

Palavras Chave

Exercise intolerance; respiratory chain enzyme; muscle biopsy