REVERSIBLE DECREASES IN N-ACETYLASPARTATE AFTER ACUTE BRAIN INJURY

N-Acetylaspartate (NAA), which constitutes the major proportion of the dominant resonance in proton MR spectra of brain, is localized in mat ure brain exclusively in neurons and neuronal processes. A decrease in NAA has been observed in many cerebral pathologies and has usually be en interpreted as an index of irreversible neuronal loss. The authors report a follow-up study of six patients with acute brain damage (four from demyelinating lesion and two from mitochondrial encephalopathy w ith lactic acidosis and stroke-like episodes [MELAS]). All patients un derwent serial MR spectroscopy examinations, The four patients with ac ute demyelinating lesions initially showed decreases in NAA in the cen ters of the lesions that ranged between 34-72% of values from homologo us brain volumes in the other hemisphere. All four patients subsequent ly showed substantial recovery of NAA as their clinical status improve d. The two patients with MELAS syndrome had large decreases of NAA sig nal (50% and 20% of normal values, respectively) from their occipital lobe lesions during the acute stroke-like episodes. After the acute ph ase of the illness a progressive increase of NAA in the same volumes w as seen in both patients (to 76% and 60% of normal values, respectivel y). These results demonstrate that significant recovery of NAA can occ ur after acute brain damage. The potential contribution of reversible neuronal dysfunction (as well as neuronal loss) must be considered in the interpretation of decreases in the NAA resonance associated with a cute brain pathology.