LACTATE STRESS TEST IN THE DIAGNOSIS OF MITOCHONDRIAL MYOPATHY

The aim of the study was to determine the sensitivity and specificity of the lactate stress test in the detection of mitochondrial myopathie s. Thirty one healthy subjects, 10 patients with non-mitochondrial myo pathy and 26 patients with mitochondrial myopathy underwent lactate st ress testing at a standardized workload of 30 W during 15 min on a bic ycle ergometer. Lactate was determined before the exercise (R1), 5, 10 , 15 min after starting the exercise (S5, S10, S15) and 15 min after f inishing the exercise (R2). A result was interpreted as pathologic if more than two of the five lactate values were above the corresponding upper reference limits. The upper reference limits for the venous lact ate at R1; S5, S10, S15 and R2 were 1.9, 2.0, 2.1, 2.0 and 1.7 mmol/l respectively. The lactate stress test was pathologic 1/10 of the non;m itochondrial myopathies and in 18/26 of the mitochondrial myopathies. The sensitivity of the lactate stress test was 69%. The specificity of the test was 90%. in conclusion, the lactate stress test proved to be helpful for evaluating the integrity of the oxidative metabolism in t he majority of patients with mitochondrial myopathy. (C) 1998 Elsevier Science B.V. All rights reserved.