Mitochondrial myopathies: current diagnosis (I)

Abstract

Mitochondrial diseases can present at any age and include a combination of multisystemic symptoms. Major manifestations of muscle involvement include infantile hypotonia, weakness, and lactic acidosis; severe exercise intolerance and easy fatigability, variable fixed weakness, often involving the extraocular muscles. Additionally, infantile or childhood encephalomyopathies have been identified in which CNS (e.g., seizures, ataxia, stroke-like episodes) and muscle symptoms coexist. Paraclinical investigations support the diagnosis and help in categorizing the mitochondrial myopathies (MM). Serum CK level may be mildly elevated in MM but are often normal; blood lactate concentration is usually elevated at rest. Electroneuromyographic features are not pathognomonic: myopathic EMG findings and reduced sensory response amplitudes. Muscle biopsy is a more specific test of mitochondrial myopathies, typically showing the presence of ragged red fibers, COX negative and SDH positive, with ultrastructural abnormal mitochondria (electron microscopy). Enzymatic and genetic tests are sometimes useful. After overviewing the current literature, a brief clinical case report is presented.