Preliminary Evaluation of Clinician Rated Outcome Measures in Mitochondrial Disease

Background: Currently there are no known cures and few effective treatments for mitochondrial disorders. It is also true there is a lack of knowledge about suitable clinician rated outcomes and how these change over time in this patient cohort. Objective: We sought to evaluate the validity and responsiveness to change of clinician rated outcome measures in patients with m.3243A>G-related mitochondrial disease. Methods: We assessed the six minute timed walk (6MTW), 10 meter walk / test (10MWT), Timed up and Go (TUG) and the 5 times sit to stand (5XSTS), in 18 patients (12 sedentary controls), at baseline and a subgroup of 10 control-matched patients following a 16-week structured aerobic exercise intervention program. Results: All outcome measures assessed were valid and able to differentiate between patients and controls. Disease severity, as measured by the Newcastle Mitochondrial Disease Adult Scale, correlated with TUG (r = 0.54, p = 0.020) and 10MWT (r = 0.47, p = 0.050). Receiver Operating Curve analysis revealed 5XSTS to be the most responsive measure (AUC 0.931; 95% CI 0.84– 1.00) with responsiveness to change, post intervention, emulating disease burden variance. Conclusions: The 5XSTS can be used to discriminate between mitochondrial patients and sedentary controls with high accuracy. The 10MWT and TUG may serve as suitable and clinically relevant clinician rated measures to track disease progression and assess intervention.