[Standardized bicycle ergometry test in mitochondrial myopathies. Indications, interferences and clinical parameters]

Exercise tests are widely used as simple, non-invasive screening methods in the differential diagnosis of metabolic myopathies. Exercise protocols have not been standardized with regard to duration of the test, workload, or monitored metabolic parameters. Potentially interfering parameters such as gender or maximal isometric force of the individuals have not been investigated. Here we describe a standardized bicycle ergometry protocol with a stepwise increasing workload between 30 and 100 watts. The venous lactate/pyruvate (L/P) ratio proved to be the one clinically most useful parameter in the functional diagnosis of mitochondrial myopathies with pathological exercise values in all nine examined patients. Additionally, the effects of coenzyme Q therapy in these patients were most clearly mirrored by changes in the L/P ratio. Nonspecifically elevated venous lactate concentrations above 5 mmol/l are rarely found in healthy female volunteers with low maximal isometric force of the M. quadriceps femoris. Other parameters such as serum free fatty acids, ketone bodies, intermediate products of the Krebs cycle or spirometric investigations add only little additional information. The exercise test described may be useful as an additional investigation in the differential diagnosis of metabolic myopathies.