Biochemical and Chemical Myopathy as Isolated Initial Manifestation of a Mitochondrial Disorder in a Competitive Swimmer.

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.