Background: Exercise tests has been used in the diagnosis of metabolic myopathies. If there is an abnormal response pattern in mild mitochondrial myopathy (MM) and her role in the initial suspect diagnostic is unknown.
Subjects and methods: Prospective study of 26 patients with mitochondrial myopathy (15 men, 11 women) and a control group of 14 sedentary volunteers (9 men, 5 woman) with similar antropometric characteristics. We have made pulmonary function tests and treadmill exercise with serial venous sampling of blood lactate, piruvate, ketone bodies, free fatty acids and creatinkinase.
Results: Patients with MM showed exercise limitation with lower maximal power (MM = 143 [47] vatts, C = 187 [40] vatts, p = 0.006), maximal oxygen uptake (MM = 27 [8] ml/min/kg, C = 40 [7] ml/min/kg, p = 0.001) and maximal oxygen pulse (MM = 11 [3] ml/beat, C = 14 [3] ml/beat, p = 0.006). For the same oxygen uptake the heart rate was higher and the anaerobic threshold was earlier in MM patients (MM = 48% [14], C = 62% [12], p = 0.01). We found a considerable slower maximal oxygen uptake in patients with lipid increase in muscle biopsy (n = 15). Acetoacetate curves, beta-hydroxybutyrate, free fatty acids and creatinkinase were similar in both groups. The exercise test was pathologic in 17/26 of the patients. The sensitivity of the exercise test for maximal oxygen uptake was 0.65.
Conclusions: The cardiopulmonary exercise test is a useful test in the suspect initial diagnostic of patients with mild mitochondrial myopathy because the majority of patients show a pathologic test.