Amplitude-integrated EEG abnormalities in two neonates with encephalopathy due to mitochondrial dysfunction (respiratory chain complex I deficiency)

Amplitude-integrated electroencephalography (aEEG) findings in hypoxic-ischemic encephalopathy characterized by secondary energy failure have been described in detail. In contrast, reports of use of aEEG in patients with encephalopathy due to primary energy failure as seen in inherited metabolic disorders are sparse. We report two cases of lethal mitochondrial encephalopathy due to mitochondrial respiratory chain complex I deficiency. We present clinical course, laboratory evaluations, aEEG, conventional electroencephalography, magnetic resonance imaging and magnetic resonance spectroscopy findings of two cases identified with mitochondrial encephalopathy between 2002 and 2007. Both infants were born at term. Both presented with intractable seizures and mild hypotonia within the first days of life, in the absence of any evidence suggestive of hypoxic-ischemic encephalopathy. Both cases were treated with multiple anticonvulsants and in neither case were seizures fully controlled. Magnetic resonance imaging in both cases revealed a structurally normal brain and case one showed subtle diffuse deep white matter signal abnormality. Magnetic resonance spectroscopy revealed no elevation of lactate. In both cases, aEEG tracings were markedly abnormal, confirmed by electroencephalography. Case one showed status epilepticus on an abnormally high amplitude background and case two presented with a mainly discontinuous background pattern with intermittent burst-suppression pattern activity. Complex I activity in skeletal muscle homogenate was abnormally low in both patients. The use of aEEG as a valuable assessment and monitoring tool in patients with metabolic encephalopathy should be further promoted.