Radiologia Brasileira - Publicação Científica Oficial do Colégio Brasileiro de Radiologia

AMB - Associação Médica Brasileira CNA - Comissão Nacional de Acreditação
Idioma/Language: Português Inglês

Vol. 53 nº 6 - Nov. / Dec.  of 2020

EDITORIAL
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H-MRS for characterizing metabolic alterations in HIV-positive patients with and without memory deficits

Autho(rs): Fabiano Reis

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Proton magnetic resonance spectroscopy (1H-MRS) provides a noninvasive method for examining a wide variety of metabolites in the human brain(1,2), including N-acetylaspartate (NAA), a compound present in neurons and axons; choline-containing compounds, which are involved in membrane synthesis and degradation; phosphocreatine and creatine, which play a major role in energy metabolism; lactate, a resultant of increased anaerobic glycolysis; lipids, which correlate with necrosis; and others, such as succinate, amino acids, glycine, glutamine, and myo-inositol. The acquisition of the localized metabolic information available from proton spectra can be correlated with magnetic resonance imaging (MRI) and other imaging methods, potentially leading to the development of a set of physiological, anatomical, and biochemical parameters, which may provide a powerful approach to investigating the underlying pathophysiology of many disorders(1). Even in a brain with a normal appearance (in structural MRI sequences), such abnormalities can be observed. Technically, detecting the absolute concentrations from spectroscopy is relatively difficult. Therefore, metabolite-to-creatine ratios are calculated, which requires us to make an assumption that creatine concentrations remain constant and stable(3). First, it is convenient and easy to acquire a 1H-MRS spectrum from a standard MRI scanner with a short echo time. The spectrum can be obtained either from a single voxel of interest or from multiple areas (multivoxel spectroscopy). That makes 1H-MRS simultaneously sensitive to metabolite changes in multiple regions(4). In addition, 1H-MRS is a noninvasive, radiation-free technique that has the advantage of monitoring disease progression(3).

The current issue of Radiologia Brasileira features an excellent article by Correa et al.(5), entitled “Posterior cingulate gyri metabolic alterations in HIV-positive patients with and without memory deficits”, in which 36 HIV-positive patients (with and without memory deficits) were compared with 22 controls. Despite the small number of patients evaluated in their study, the authors demonstrated that choline/creatine ratios in the posterior cingulate gyri were significantly higher in the HIV-positive patients (with and without memory deficits) than in the controls. The authors also corroborated data presented in previous studies(6–8), as well as underscoring the fact that there are direct and indirect mechanisms, as well as certain events, associated with HIV encephalitis. An elevated choline level may provide a useful marker for the early effects of HIV infection on the central nervous system before the onset of dementia and a reduction in NAA(6).

Glycerophosphocholine (GPC) and phosphocholine (PC) represent the major constituents of the in vivo 1H-MRS-detected choline resonance, to which free choline makes only a minor contribution. If membrane damage occurs subsequent to HIV infection, choline-containing compounds (GPC, PC, and free choline) may be released, thus increasing the intensity of the choline signal(9). Supporting this hypothesis is the finding of significant damage to and vacuolization of the dendritic tree in HIV encephalitis(7). That may also reflect an increase in the number of macrophages and microglia in the brains of patients with AIDS. The use of 1H-MRS provides a sensitive, noninvasive means of detecting alterations in the microenvironment of HIV. A reduction in NAA occurs only in patients suffering from more advanced dementia, and an increased choline level may therefore be a more reliable marker of early brain abnormalities associated with HIV infection. In a previous study(8), an elevated choline peak before the onset of dementia was demonstrated in HIV-infected patients and, as in the Correa et al. study(5), was not found to correlate with neuropsychological performance.


REFERENCES

1. Faria AV, Reis F, Zanardi VA, et al. The pattern of proton magnetic resonance spectroscopy in non-neoplastic encephalic lesions. Arq Neuropsiquiatr. 2004;62:429–36.

2. Leite CC. Espectroscopia de prótons por ressonância magnética. Radiol Bras. 2001;34(1):v–vi.

3. Wang H, Tan L, Wang HF, et al. Magnetic resonance spectroscopy in Alzheimer’s disease: systematic review and meta-analysis. J Alzheimers Dis. 2015;46:1049–70.

4. Angelie E, Bonmartin A, Boudraa A, et al. Regional differences and metabolic changes in normal aging of the human brain: proton MR spectroscopic imaging study. AJNR Am J Neuroradiol. 2001;22:119–27.

5. Corrêa DG, van Duinkerken E, Zimmermann N, et al. Posterior cingulate gyri metabolic alterations in HIV-positive patients with and without memory deficits. Radiol Bras 2020;53:359–65.

6. Tracey I, Carr CA, Guimaraes AR, et al. Brain choline-containing compounds are elevated in HIV-positive patients before the onset of AIDS dementia complex: a proton magnetic resonance spectroscopic study. Neurology. 1996;46:783–8.

7. Wiley CA, Masliah E, Morey M, et al. Neocortical damage during HIV infection. Ann Neurol. 1991;29:651–7.

8. Meyerhoff DJ, Bloomer C, Cardenas V, et al. Elevated subcortical choline metabolites in cognitively and clinically asymptomatic HIV+ patients. Neurology. 1999;52:995–1003.

9. Barker PB, Breiter SN, Soher BJ, et al. Quantitative proton spectroscopy of canine brain: in vivo and in vitro correlations. Magn Reson Med. 1994;32:157–63.










1. Associate Professor of Neuroradiology and Chair of the Neuroradiology Department at the Universidade Estadual de Campinas (Unicamp), Campinas, SP, Brazil

Email: fabianoreis2@gmail.com

https://orcid.org/0000-0003-2256-4379
 
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