Temporal window of metabolic brain vulnerability to concussion: A pilot H-1 magnetic resonance spectroscopic study in concussed athletes - Part III

OBJECTIVE: In the present study, the occurrence of the tem'! oral window of brain vulnerability was evaluated in concussed athletes by measurinj r, N-acetylaspartate (NAA) using proton magnetic resonance ('H-MR) spectroscopy. METHODS: Thirteen nonprofessional athletes who had a spc t-related concussive head injury were examined for NAA determination by means of IH]MR spectroscopy at 3, 15, and 30 days postinjury. All athletes but three suspended their,hysical activity. Those who continued their training had a second concussive event and I underwent further examination at 45 days from the initial injury. The single case of orle professional boxer, who was studied before the match and 4, 7, 15, and 30 days aft(''!r a knockout, is also presented. Before each magnetic resonance examination, patient, were asked for symptoms of mild traumatic brain injury, including physical, cognitive; lemotional, and sleep disturbances. Data for I H-MR spectroscopy recorded in five n4pal, age-matched, control volunteers, who were previously screened to exclude previolJ1 s head injuries, were used i for comparison. Serniquantitative analysis of NAA relative to creatine (Cr)- and choline (Cho)-containing compounds was performed from proton sl Iectra obtained with a 3-T magnetic resonance system. RESULTS: Regarding the values of the NAA-to-Cr ratio (2.21 ji. 0.11) recorded in control patients, singly concussed athletes, at 3 days after the concuss ion, showed a decrease of 18.5% (1.80 -_ 0.04; P < 0.001). Only a modest 3% recover was observed at 15 days j, r (1.88 0.1; P< 0.001); at 30 days postinjury, the NAA-to-Cr raio was 2.15 -_ 0.1, revealing full metabolic recovery with values not significantly clifflE I rent from those of control patients. These patients declared complete resolution of symj)tctms at the time of the 3day study. The three patients who had a second concussive inj lry before the 15-day study showed an identical decrease of the NAA-to-Cr ratio at 3 da ls (1.78 4- 0.08); however, at 15 days after the second injury, a further diminution of the NAA-to-Cr ratio occurred (1.72 0.07; P < 0.05 with respect to singly concussed athl('!tes). At 30 days, the NAAto-Cr ratio was 1.82 0. 1, and at 45 days postinjury, the NA, I -to-Cr ratio showed com1! plete recovery (2.07 0. 1; not sign if icant with respect to con irol patients). This group of patients declared a complete resolution of symptoms at the ti' I,re of the 30-day study. CONCLUSION: Results of this pilot study carried out in a c( I)hort of singly and doubly I concussed athletes, examined by I H-MR spectroscopy for the I ir NAA cerebral content at different time points after concussive events, demonstrate tha also in humans, concussion opens a temporal window of brain metabolic imbalancejl the closure of which does not coincide with resolution of clinical symptoms. The reco vpry of brain metabolism is I not linearly related to time. A second concussive event prolon ed the time of NAA nor!19 malization by 15 days. Although needing confirmation in a larger group of patients, these 1 5 results show that NAA measurement by 'H-MR spectroscopylis a valid too] in assessing the full cerebral metabolic recovery after concussion, thereb ylsuggesting its use in helpft