Reversible decreases in <i>N</i>‐acetylaspartate after acute brain injury

TLDR

N‑acetylaspartate (NAA) is a neuronal marker whose reduction in brain MR spectra is commonly linked to irreversible neuronal loss, yet reversible dysfunction may also explain such decreases in acute pathology. The study followed six patients with acute brain injury—four with demyelinating lesions and two with MELAS—using serial magnetic resonance spectroscopy to track NAA changes over time. In all six patients, NAA levels initially dropped markedly but subsequently recovered toward normal, demonstrating that NAA reductions after acute brain injury can be reversible.

Abstract

Abstract N ‐Acetylaspartate (NAA), which constitutes the major proportion of the dominant resonance in proton MR spectra of brain, is localized in mature brain exclusively in neurons and neuronal processes. A decrease in NAA has been observed in many cerebral pathologies and has usually been 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 with lactic acidosis and stroke‐like episodes [MELAS]). All patients underwent serial MR spectroscopy examinations. The four patients with acute demyelinating lesions initially showed decreases in NAA in the centers of the lesions that ranged between 34‐72% of values from homologous brain volumes in the other hemisphere. All four patients subsequently showed substantial recovery of NAA as their clinical status improved. The two patients with MELAS syndrome had large decreases of NAA signal (50% and 20% of normal values, respectively) from their occipital lobe lesions during the acute stroke‐like episodes. After the acute phase of the illness a progressive increase of NAA in the same volumes was seen in both patients (to 76% and 60% of normal values, respectively). These results demonstrate that significant recovery of NAA can occur 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 acute brain pathology.