Respiratory failure revealing mitochondrial myopathy in adults

Two patients, a 70-yr-old black woman and a 56-yr-old black man, presented with respiratory failure unexplained by intrinsic lung disease. Both had been dependent on a respirator for several weeks. No abnormalities of the central or peripheral nervous system or long-standing muscle weakness was noted. The findings from ophthalmologic and cardiac evaluations were normal. The serum creatinine kinase concentration was mildly elevated in case 1, and needle electromyography showed myopathic potentials in case 2. In both instances, muscle biopsy established the diagnosis of mitochondrial myopathy. Biochemical studies of muscle extracts showed partial deficiency of complex 3 in patient 2 and of complex 4 in patient 1. Both patients were weaned from the ventilator after long periods of ventilatory assistance. These observations document a hitherto undescribed presentation of adult-onset mitochondrial myopathy.