A novel exercise testing algorithm to diagnose mitochondrial myopathy.

Introduction: Oxygen uptake efficiency slope (OUES) is a noninvasive cardiopulmonary exercise testing (CPET) measurement based on oxygen uptake (V˙O2) and minute ventilation (V˙E) and is a marker of the efficiency of oxygen utilization by the body. However, it has not been studied in mitochondrial disorders. We explored noninvasive CPET parameters, including OUES, as a way to reliably diagnose mitochondrial myopathy. Methods: We performed cycle ergometer maximal exercise testing on definite and suspected mitochondrial myopathy subjects (MM‐D and MM‐S) and their age‐ and sex‐matched controls. OUES was corrected for body surface area (OUES/BSA) to eliminate the effect of body size. Results: A total of 40 participants, including 20 MM‐D (n = 13; 6 males; aged 14‐64 years) and 7 MM‐S (5 males, aged 11‐30 years) subjects and 20 controls, completed the study. MM‐D subjects showed lower aerobic fitness than controls. OUES/BSA was lower in MM‐D subjects, suggesting inefficient oxygen utilization. Area under the curve (AUC) and 95% confidence interval (CI) for OUES/BSA (AUC, 0.91; 95% CI, 0.80‐1.00), peak V˙O2 percent predicted (AUC, 0.95; 95% CI, 0.86‐1.00), and V˙O2/work slope (AUC, 0.94; 95% CI, 0.85‐1.00) showed excellent ability to diagnose mitochondrial myopathy in MM‐D subjects. We applied a diagnostic approach based on the parameters just noted to MM‐S subjects and their controls and were able to support or disprove the diagnosis of mitochondrial myopathy. Discussion: We proposed and applied an approach based on the aformentioned three CPET parameters to diagnose mitochondrial myopathy reliably and found it to be clinically useful. [ABSTRACT FROM AUTHOR]