Acute mitochondrial myopathy with respiratory insufficiency and motor axonal polyneuropathy

Mitochondrial myopathies (MMs) are mainly presented with chronic muscle weakness and accompanied with other syndromes. MM with acute respiratory insufficiency is rare.To reveal the clinical, pathological and molecular characteristics of a life-threatening MM.Muscle biopsy and enzyme staining were performed in skeletal muscles. Mitochondrial DNA (mtDNA) sequencing was analyzed and heteroplasmy were quantified by pyrosequencing.All three patients had tachycardia, acute lactic acidosis, dyspnea and sudden severe muscle weakness. Two patients had calf edema and abdominal pain, and one had a heart attack. Electromyography in two patients showed dramatically decreased axonal amplitudes of motor nerves. Muscle biopsies showed ragged red fibers and dramatic mitochondrial abnormality. A mtDNA m.3243A>G mutation was identified in Patient 1 (mutation load: 29% in blood and 73% in muscle) and Patient 3 (79% in blood and 89% in muscle). A mtDNA m.8344A>G mutation was found in Patient 2 (mutation load 80.4% in blood).MM characterized by lactic acidosis, respiratory failure and acute motor axonal neuropathy is life threatening.