Short ReportsBiochemical and Chemical Myopathy as Isolated Initial Manifestation of a Mitochondrial Disorder in a Competitive SwimmerFinsterer, Josef MD, PHD Author Information Neurology and Neurophysiology Center, Vienna, Austria. Reprints: Josef Finsterer, MD, PHD, KAR Vienna, Neurology and Nerophysiology Center, Postfach 20, 1180 Vienna, Austria (e-mail: [email protected]). The author reports no conflicts of interest. J. Finsterer: design, literature search, discussion, first draft, critical comments. Journal of Clinical Neuromuscular Disease: December 2022 - Volume 24 - Issue 2 - p 103-105 doi: 10.1097/CND.0000000000000406 Buy Metrics Abstract Isolated and asymptomatic elevation of creatine kinase (hyper-CKemia) can be one of the initial manifestations of a mitochondrial disorder (MID). We present an asymptomatic patient with accidently detected isolated hyper-CKemia and respiratory chain dysfunction as indicators of a chemical and biochemical MID, respectively. A 23-year-old man who performed competitive sport (swimming) underwent workup for accidentally detected asymptomatic and isolated hyper-CKemia. Clinical neurologic examination was normal, but blood tests revealed elevation of creatine kinase (CK), aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and aldolase. Lactate stress testing on a bicycle ergometer was normal. Needle electromyography was noninformative, but muscle biopsy was indicative of a MID, and biochemical investigations revealed a combined complex-II, -III, and -IV defect. Hyper-CKemia persisted asymptomatically over the next 15 years, and he continued with his sports activities. In conclusion, asymptomatic hyper-CKemia together with multiple respiratory chain complex deficiencies can be the only manifestations of a MID over years. Asymptomatic chemical or biochemical MIDs may profit from continuous physical activity. Workup for isolated persisting hyper-CKemia may reveal subclinical mitochondrial pathology in single cases. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.