Delayed manifestation of mitochondrial myopathy--complex I and IV deficiency of the mitochondrial respiratory chain with progressive paresis]

We describe a 53-year-old patient with a progressive mitochondrial myopathy of late-onset, restricted to skeletal muscle only without external ophthalmoplegia. The myopathy developed at the age of 46 years initially with exercise intolerance and subsequently progressive permanent muscle weakness. Muscle biopsy revealed severe myopathic changes, ragged red fibers, and a marked multifocal cytochrome-c-oxidase deficiency. Biochemical analysis showed a deficiency of complexes I and IV of the mitochondrial respiratory chain. Genetic analysis of mitochondrial DNA revealed no deletions. Mitochondrial myopathies restricted to skeletal muscle have to be considered in the differential diagnosis of late-onset progressive myopathies.