The aerobic forearm exercise test, a non-invasive tool to screen for mitochondrial disorders.

The diagnosis of a mitochondrial disorder is often difficult. Therefore, new approaches and diagnostic criteria are being developed. One of these tests is the aerobic forearm exercise test, a screening tool that can contribute to assess whether or not the patient suffers from a mitochondrial myopathy. With this simple, non-invasive test, the oxidative metabolism of muscle can be evaluated in rest and during exercise. We performed the aerobic forearm exercise test in patients with a mitochondrial disorder and an identified pathogenic gene mutation, in patients with a suspected mitochondrial disorder based on their clinical presentation and biochemical results, but without a molecular diagnosis, and in patients with atypical fatigue and no characteristics of a mitochondrial myopathy. In the first two groups, abnormal oxygen extraction from the blood during exercise was observed in four out of twelve patients. In the third group no abnormalities were found. The number of patients that we could test so far was limited, but all the patients experienced the aerobic forearm exercise as an easy test. We would like to stimulate clinicians to perform this test whenever a mitochondrial myopathy is suspected, as it can be a valuable diagnostic screening tool.