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Prognostic value of MR spectroscopy in patients with acute excitotoxic encephalopathy
Journal of the Neurological Sciences xxx (xxxx) xxxx
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Prognostic value of MR spectroscopy in patients with acute excitotoxic encephalopathy ⁎
Jun-ichi Takanashia, , Yuka Murofushia, Nozomi Hiraia, Kentaro Sanoa, Emiyu Matsuoa, Keito Saitob, Kumi Yasukawaa, Hiromichi Hamadaa a b
Department of Pediatrics, Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Japan Department of Medical Technology and Image Laboratory, Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Excitotoxic encephalopathy Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) Mild encephalopathy associated with excitotoxicity (MEEX) MR spectroscopy N-acetyl aspartate Prognosis
Purpose: Acute excitotoxic encephalopathy is the most common encephalopathy syndrome in Japan, and consists of acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) and mild encephalopathy associated with excitotoxicity (MEEX). Neurological sequelae remain in approximately 70% of patients with AESD, however, it is difficult to predict the prognosis early in the course. We evaluated the brain metabolites observed on MRS as to whether they can predict the neurological outcome. Methods: 16 previously healthy Japanese patients with excitotoxic encephalopathy (8 with AESD and 8 with MEEX) were included in this study. MR spectroscopy (MRS) was acquired from the fronto-parietal white matter (TR/TE = 5000/30 msec) with a 3.0 T scanner. Quantification of metabolites was performed using an LCModel. Neurological outcome was assessed with the Pediatric Cerebral Performance Category score, score 1 being classified as G1 (normal), scores 2 and 3 as G2 (mild to moderate), and scores 4–6 as G3 (severe). Results: MRS data which predict a poor neurological outcome (G2 and 3) include the following: decreased Nacetyl aspartate (NAA) (sensitivity 88%, specificity 100%), decreased creatine (47%, 100%), increased lactate (47%, 100%), and decreased glutamate (sensitivity 35%, specificity 100%). Limited to the acute stage within seven days of onset, those for a poor prognosis are as follows, decreased NAA (88%, 100%), decreased creatine (38%, 100%), and increased lactate (38%, 100%). Conclusion: MRS is useful for prognosis prediction of acute excitotoxic encephalopathy. Decreased NAA will be the most effective metabolite for neurological prognosis prediction.
1. Introduction Acute infectious encephalopathy is frequently observed in Japanese children (around 600 patients per year) [1], and has been classified into three categories based on the suspected pathomechanism, i.e., that associated with metabolic errors (e.g., Reye syndrome), cytokine storms (e.g., acute necrotizing encephalopathy), and excitotoxicity, respectively [2]. Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a representative excitotoxic encephalopathy, and is the most common encephalopathy syndrome in Japan (around 200 patients per year), but is rarely observed in other countries, such as European countries or the US [3,4]. AESD is characterized clinically by biphasic seizures, i.e., a prolonged febrile seizure (early seizure) on day
1, followed by a cluster of complex partial seizures (late seizures) on days 4 to 6; and radiologically by delayed reduced diffusion in the subcortical white matter (so-called bright tree appearance) on days 3 to 9 [3,4]. Excitotoxic injury with delayed (or apoptotic) neuronal death is hypothesized as a possible pathomechanism based on MRS findings showing an increase of glutamate (Glu) followed by glutamine (Gln) during the acute to subacute stages [5,6]. Mild encephalopathy associated with excitotoxicity (MEEX) shows impaired consciousness lasting for more than 24 h most often with seizures, but without a biphasic clinical course, bright tree appearance on diffusion-weighted images, hypercytokinemia, or metabolic errors [7,8]. MRS in patients with MEEX also shows acute Glu elevation followed by subacute Gln elevation (days 3 to 8) [7,8], which is identical to that observed in AESD.
Abbreviations: AESD, acute encephalopathy with biphasic seizures and late reduced diffusion; MEEX, mild encephalopathy associated with excitotoxicity; MRS, magnetic resonance spectroscopy; NAA, N-acetyl aspartate; Cr, creatine; Cho, choline; mIns, myo-inositol; Glu, glutamate; Gln, glutamine; Lac, lactate ⁎ Corresponding author at: Department of Pediatrics, Tokyo Women's Medical University Yachiyo Medical Center, 477-96 Owadashinden, Yachiyo-shi, 276-8524, Japan. E-mail address: [email protected] (J.-i. Takanashi). https://doi.org/10.1016/j.jns.2019.116636 Received 11 October 2019; Received in revised form 25 November 2019; Accepted 14 December 2019 0022-510X/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Jun-ichi Takanashi, et al., Journal of the Neurological Sciences, https://doi.org/10.1016/j.jns.2019.116636
Journal of the Neurological Sciences xxx (xxxx) xxxx
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MRS findings in MEEX may indicate that a neurochemical process whereby the excessive Glu released from presynaptic neurons under mild excitotoxic conditions is successfully processed into Gln by astrocytes through a prompt Glu-Gln cycle, which can protect neurons from delayed death [7,8]. AESD and MEEX are, therefore, considered to constitute the excitotoxic encephalopathy spectrum. Neurological sequelae remain in approximately 70% of patients with AESD [1,2], however, it is difficult to predict the prognosis severity early in the course. We, thus, evaluated the brain metabolites in vivo observed on MRS as to whether they can predict the outcome of excitotoxic encephalopathy (AESD and MEEX), which may contribute to early therapeutic intervention and an improved neurologic outcome. 2. Materials and methods 20 Japanese patients with excitotoxic encephalopathy were hospitalized at our hospital from April 2015 to March 2019. Among them, 4 AESD patients with a neurological disorder prior to the onset of encephalopathy (2 patients with a chromosomal abnormality, one with cerebral palsy, and one with septo-optic dysplasia) were excluded. Thus, 16 previously healthy patients with excitotoxic encephalopathy (8 with AESD and 8 with MEEX) were included in this study. A diagnosis of AESD or MEEX was given based on the clinical and radiological criteria previously reported [4,8,9]. One patient with AESD [6] and 7 patients with MEEX [7,8] have been reported previously for Glu and Gln derangement on MRS. The age of the 16 patients ranged from 0.5 to 8 years old (6 patients being 0.5 to 1 year, 9 patients, 1–2 years, and one patient, 8 years). The treatment included methylprednisolone pulse therapy (15 patients), normothermia (36.0–36.5 °C, 16 patients), edaravone (5 patients), a vitamin cocktail (vitamin B1, B2, B6, and Lcarnitine for 6 patients), and anticonvulsive drugs, such as continuous intravenous infusion of midazolam (4 patients) and fosphenytoin (5 patients), based on the clinical guidelines for acute encephalopathy [9]. Neurological outcome was assessed at least after 6 months' observation using the Pediatric Cerebral Performance Category score, which has six categories: normal (score 1), mild disability (score 2), moderate disability (score 3), severe disability (score 4), coma or vegetative state (score 5), and brain death (score 6). In this study, patients with score 1 were classified as grade 1 (G1, normal), ones with scores 2 and 3 as grade 2 (G2, mild to moderate), and ones with scores 4–6 as grade 3 (G3, severe). MRS with a 3.0 T scanner (Ingenia CX 3.0 T; Philips Healthcare, Best, the Netherlands) was performed by the same method as previously reported [6], that is, point resolved spectra were obtained using TR of 5000 msec, TE of 30 msec, and NEX of 32, and acquired from the fronto-parietal white matter with a voxel size of 4.5 cm3. MRS studies were performed 35 times in total, that is, 4 times for one patient, 3 times for 3, twice for 10, and once for 2. 15 MRS studies were performed within 7 days after the onset of encephalopathy. Quantification of metabolites, including N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), myo-inositol (mIns), lactate (Lac), Glu, and Gln, was performed using an LCModel [6]. The concentration of each metabolite for aged-matched controls (0.5–1 years, 1–2 years, and 6–10 years), who were studied to evaluate disorders such as mild psychomotor retardation, headache or an enlarged head circumference, and had no identified MRI abnormality, are shown in the legend to Fig. 3. Lac was judged to be abnormal when it exceeded 1.3 mM, and for other metabolites, a value exceeding the mean ± 3SD for age-matched controls was regarded as abnormal. This study was approved by IRB of Tokyo Women's Medical University (#3535R, 3123R4).
Fig. 1. MRI in a 1-year-old female with G2 AESD on day 6 shows the bright tree appearance on diffusion-weighted image (A). MRS (B) reveals decreased NAA (4.15 mM) and Cr (3.73 mM), and increased Lac (1.40 mM) and Gln (5.35 mM) with normal Glu (5.99 mM) (B).
Fig. 2. MRS in a 2-year-old male with G1 MEEX on day 5 shows increased Gln (3.13 mM) with normal NAA (7.36 mM), Cr (4.58 mM), and Glu (6.64 mM) without a Lac peak.
G1 for 9 patients (1 AESD and 8 MEEX, 18 MRS studies, Fig. 2). Fig. 3 shows the concentrations of metabolites observed on MRS over time. NAA, Cr, Lac, and Glu are considered to be correlated with the neurological outcome. Among the 9 G1 patients, there was no obvious MRS distinction between AESD (blue squares with red margins) and MEEX (blue squares). MRS in G2 and G3 (Fig. 3-A) showed a decreased NAA concentration (less than mean-3SD, under 5.0 mM for under 1 year, under 5.6 mM for over 1 year) in 15 of 17 studies (88%), that is, 11 of 12 (92%) in G2 and 4 of 5 (80%) in G3. On the other hand, none of the 18 MRS studies in G1 (Fig. 3-B) showed such a decrease of NAA. Even in
3. Results The prognoses of the 16 patients were G3 for 2 patients (2 AESD, 5 MRS studies), G2 for 5 patients (5 AESD, 12 MRS studies, Fig. 1), and 2
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Fig. 3. The concentrations of metabolites in the brain over time in excitotoxic encephalopathy. The X and Y axes show days after onset and metabolite concentration (mmol/l). The red dotted and red lines indicate the mean-3SD metabolite concentrations at 0.5–1 and 1–2 years, respectively. A and B indicate the NAA concentrations of G2 AESD (red squares) and G3 AESD (black squares), and G1 MEEX (blue squares), and G1 AESD (blue squares with red margins), respectively. The concentrations of Cr, Lac, and Glu in G2 and 3, and G1 are shown in C and D, E and F, and G and H. Means and SD for each metabolite concentration for aged-matched controls are as follows; NAA for 0.5–1 years, 5.9 ± 0.3 (mM, mean ± SD), for 1–2 years, 6.8 ± 0.4 mM, for 6–10 years, 9.3 ± 0.4 mM; Cr for 0.5–1 years, 4.4 ± 0.2 mM, for 1–2 years, 4.7 ± 0.2 mM, for 6–10 years, 4.8 ± 0.3 mM; and Glu for 0.5–1 years, 6.1 ± 0.4 mM, for 1–2 years, 6.8 ± 0.4 mM, for 6–10 years, 5.6 ± 0.6 mM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The most important finding in this study is that MRS is useful for prognosis prediction as well as for the diagnosis of acute encephalopathy associated with excitotoxicity. In the acute stage within 7 days of onset, MRS data which will predict a poor neurological outcome (G2 and 3) include the following: in order of increasing sensitivity; decreased NAA (sensitivity 88%, specificity 100%), decreased Cr (sensitivity 38%, specificity 100%), and increased Lac (sensitivity 38%, specificity 100%). Poor prognostic factors throughout the course of the disease are as follows; decreased NAA (sensitivity 88%, specificity 100%), decreased Cr (sensitivity 47%, specificity 100%), increased Lac (sensitivity 47%, specificity 100%), and decreased Glu (sensitivity 35%, specificity 100%). Because the specificities for predicting a poor outcome are all 100%, if these metabolite abnormalities are observed on MRS during the course of the disease, it can be deduced that the prognosis will be poor. Because decreased NAA exhibits the highest sensitivity (88%) even in the acute stage within 7 days of onset, it will be the most effective metabolite for neurological prognosis prediction. This finding is compatible with a previous report that two AESD patients with neurological sequelae showed decreased NAA during the course of the disease [5]. NAA is synthesized in neuronal mitochondria, being almost entirely confined to neurons and their axons, thus, it is considered to be a neuron- and axon-specific marker [11]. The markedly decreased NAA observed in G2 and G3 patients may, therefore, reflect neuronal or axonal dysfunction or loss, which later results in neurological sequelae. This may also explain why NAA after the subacute stage decreases more markedly in G3 than in G2. Other metabolites that would be useful for predicting the prognosis of excitotoxic encephalopathy include decreased Cr, increased Lac, and decreased Glu. Cr observed on MRS represents the total amount of Cr and phosphocreatine present in the Cr kinase shuttle, which is related to the energy reservoir in cells with a high energy demand [11,12]. The decrease of Cr observed in G2 and G3 patients may be due to cerebral energy failure, which reasonably results in a poor neurological prognosis. Lac is the end product of glycolysis, and it increases under conditions of anaerobic glycolysis, such as in failure of energy supply [11,12]. The increased Lac observed in G2 and G3 patients may also suggest cerebral energy failure, leading to neurological sequelae. Glutamatergic neurons release Glu into the synaptic cleft, where it is taken up by surrounding astrocytes through glutamate transporters [6,13]. Glu taken up by astrocytes is amidated to a harmless compound, Gln, which is returned to the neurons for re-use as Glu, completing the Glu (in neuron)-Gln (in astrocyte) cycle [14]. MRS in patients with excitotoxic encephalopathy (AESD or MEEX) reveals acute Glu elevation within a few days of onset, which changes to subacute Gln elevation on days 4–12 [6,8], suggesting a disrupted Glu-Gln cycle due to hyperexcitotoxicity may play an important role as a pathogenic mechanism. Elevated Glu or Gln in the acute to subacute stages, which was observed in all patients in this study, however, could not predict the neurological prognosis. Conversely, decreased Glu after the subacute stage (> day 10) was a poor neuro-prognosis factor. As Glu is present in all cell types, with the largest pool in glutamatergic neurons and smaller ones in GABAergic neurons and astrocytes, neuronal dysfunction or loss reasonably results in decreased Glu, which also leads to a poor neurological prognosis. The usefulness of MRS in predicting the prognosis has also been
the acute stage within 7 days of onset, NAA in G2 and 3 was less than the mean-3SD in 7 of 8 MRS studies (88%), that is, 6/6 (100%) in G2 and 1/2 (50%) in G3, respectively. After the subacute stage (later than 7 days of onset), the NAA decrease in G3 was more prominent than that in G2. Decreased Cr concentrations (less than mean-3SD) were observed in 8 of 17 MRS studies (47%) in G2 and G3, that is, 4 of 12 (33%) in G2, and 4 of 5 (80%) in G3 (Fig. 3-C). While, none of the 18 MRS studies in G1 (Fig. 3-D) showed a decrease of the Cr concentration. In the acute stage within 7 days of onset, decreases of Cr in G2 and G3 were observed in 3/8 (38%), that is, 2/6 (33%) in G2 and 1/2 (50%) in G3, respectively. Lac concentrations over 1.3 mM (11.7 mg/dl) were observed in none of the 18 MRS studies (0%) in G1 (Fig. 3-F), and 8 of 17 (47%) in G2 and G3, that is, 4 of 12 (33%) in G2 and 4 of 5 (80%) in G3 (Fig. 3E). In the acute stage within 7 days of onset, increased Lac concentrations were seen in 3/8 (38%) in G2 and G3, that is, 2/6 (33%) in G2 and 1/2 (50%) in G3, respectively. Decreased Glu concentrations (less than mean-3SD) were observed in none of the 18 MRS studies (0%) in G1 (Fig. 3-H), and 6 of 17 (35%) in G2 and G3 (all later than 10 days) (Fig. 3-G), that is, 4 of 12 (33%) in G2, and 2 of 5 (40%) in G3. Other metabolites, Cho, mIns and Gln, seemed unable to predict the neurological prognosis. That is, increased or decreased Cho (over mean + 3SD or less than mean-3SD) was observed in 5 of 17 studies (increases and decreases being 3 and 2 each) in G2 and G3 (Supplementary Fig. A), and 5 of 18 studies (increases and decreases being 4 and 1 each) in G1 (Supplementary Fig. B). Increased or decreased mIns was observed in 3 of 17 studies (increases and decreases being 1 and 2 each) in G2 and G3 (Supplementary Fig. C), and none of 18 studies in G1 (Supplementary Fig. D). Increased Gln in the acute stage, which is the diagnostic key for the diagnosis of AESD and MEEX, was observed in all 6 patients with G2 and G3, and all 7 patients with G1 so examined (Supplementary Fig. E, F). Throughout the course of the illness, increased Gln was observed in 10/17 studies in G2 and G3, and 9/18 studies in G1. There was no correlation between treatment and prognosis (G2 and 3 versus G1): methylprednisolone pulse therapy (7/7 for G2 and 3, and 8/9 for G1), normothermia (7/7 and 9/9), edaravone (3/7 and 2/9, p = .37 [Fisher's exact test]), a vitamin cocktail (2/7 and 4/9, p = .45), continuous intravenous infusion of midazolam (2/7 and 2/9, p = .61), and fosphenytoin (3/7 and 2/9, p = .37).
4. Discussion MRI is usually performed early for children with suspected encephalopathy to detect characteristic lesions of encephalopathy syndromes, such as the bright tree appearance in AESD, a splenial lesion in clinically mild encephalitis/encephalopathy with a reversible splenial lesion, and bilateral thalamic lesions in acute necrotizing encephalopathy [2–4]. MRS performed at the same time as MRI will contribute to the diagnosis of excitotoxic encephalopathy through the detection of elevated Glu or Gln [5–8]. If MRS in the acute stage is also able to predict the neurological prognosis, it may change the treatment strategy, leading to aggressive therapeutic intervention such as hypothermia [10]. 4
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References
reported in patients with hypoxic-ischemic encephalopathy [12]. Cerebral injury secondary to hypoxic-ischemic encephalopathy disrupts mitochondrial ATP synthesis, leading to neuronal depolarization inducing Glu release, resulting in delayed neuronal cell death [15], which is also postulated in excitotoxic encephalopathy. MRS findings related to a poor neurological prognosis in patients with hypoxic-ischemic encephalopathy include decreases of NAA and Cr, and an increase of Lac [12], which are consistent with those in excitotoxic encephalopathy observed in this study. The same prognostic factors on MRS in both conditions associated with excitotoxicity may indicate that the results of this study are reasonable and reliable. From the viewpoints of clinical symptoms and laboratory findings, a few reports proposed prognostic factors for AESD. They included prolonged seizures at the onset and loss of consciousness 24 h after the onset [16], coma and involuntary movements before the late seizures, high levels of serum alanine aminotransferase, more extensive lesions of the cerebrum and basal ganglia [17], and coma 12–24 h after the onset and elevation of serum creatinine and alanine aminotransferase [18]. By combining the previously presented poor prognostic factors and MRS findings in this study, it will be possible to obtain a more accurate prognosis of excitotoxic encephalopathy. The limitation of this study is the small number of patients from one hospital; because we had to treat all patients without any evidencebased protocol, the timing or combination of therapies for encephalopathy was not uniform. MRS, which is essential for the diagnosis of MEEX, is not always possible in Japanese hospitals. Because the concentrations of metabolites observed on MRS depend on the MR manufacturer, magnetic field strength and measurement sequences, agematched control metabolite concentration data is necessary for each institution to apply the MRS results of this study. In conclusion, MRS data which will predict a poor neurological outcome include decreased NAA, decreased Cr, increased Lac, and decreased Glu. MRS is useful for prognosis prediction of acute excitotoxic encephalopathy as well as for a diagnosis, and may contribute to early therapeutic intervention and an improved neurologic outcome. Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jns.2019.116636.
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Acknowledgement This study was in part supported by JSPS KAKENHI Grant Number JP19K08237, Ministry of Health, Labor and Welfare, Grant-in-Aid for Research on Measures for Intractable Diseases (H30-Nanji-Ippan-007), and AMED, Practical Research Project for Rare/Intractable Diseases (19ek0109270). Declaration of Competing Interest All authors declare no conflicts of interest.
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Journal of the Neurological Sciences journal homepage: www.elsevier.com/locate/jns
Prognostic value of MR spectroscopy in patients with acute excitotoxic encephalopathy ⁎
Jun-ichi Takanashia, , Yuka Murofushia, Nozomi Hiraia, Kentaro Sanoa, Emiyu Matsuoa, Keito Saitob, Kumi Yasukawaa, Hiromichi Hamadaa a b
Department of Pediatrics, Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Japan Department of Medical Technology and Image Laboratory, Tokyo Women's Medical University Yachiyo Medical Center, Yachiyo, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: Excitotoxic encephalopathy Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) Mild encephalopathy associated with excitotoxicity (MEEX) MR spectroscopy N-acetyl aspartate Prognosis
Purpose: Acute excitotoxic encephalopathy is the most common encephalopathy syndrome in Japan, and consists of acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) and mild encephalopathy associated with excitotoxicity (MEEX). Neurological sequelae remain in approximately 70% of patients with AESD, however, it is difficult to predict the prognosis early in the course. We evaluated the brain metabolites observed on MRS as to whether they can predict the neurological outcome. Methods: 16 previously healthy Japanese patients with excitotoxic encephalopathy (8 with AESD and 8 with MEEX) were included in this study. MR spectroscopy (MRS) was acquired from the fronto-parietal white matter (TR/TE = 5000/30 msec) with a 3.0 T scanner. Quantification of metabolites was performed using an LCModel. Neurological outcome was assessed with the Pediatric Cerebral Performance Category score, score 1 being classified as G1 (normal), scores 2 and 3 as G2 (mild to moderate), and scores 4–6 as G3 (severe). Results: MRS data which predict a poor neurological outcome (G2 and 3) include the following: decreased Nacetyl aspartate (NAA) (sensitivity 88%, specificity 100%), decreased creatine (47%, 100%), increased lactate (47%, 100%), and decreased glutamate (sensitivity 35%, specificity 100%). Limited to the acute stage within seven days of onset, those for a poor prognosis are as follows, decreased NAA (88%, 100%), decreased creatine (38%, 100%), and increased lactate (38%, 100%). Conclusion: MRS is useful for prognosis prediction of acute excitotoxic encephalopathy. Decreased NAA will be the most effective metabolite for neurological prognosis prediction.
1. Introduction Acute infectious encephalopathy is frequently observed in Japanese children (around 600 patients per year) [1], and has been classified into three categories based on the suspected pathomechanism, i.e., that associated with metabolic errors (e.g., Reye syndrome), cytokine storms (e.g., acute necrotizing encephalopathy), and excitotoxicity, respectively [2]. Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a representative excitotoxic encephalopathy, and is the most common encephalopathy syndrome in Japan (around 200 patients per year), but is rarely observed in other countries, such as European countries or the US [3,4]. AESD is characterized clinically by biphasic seizures, i.e., a prolonged febrile seizure (early seizure) on day
1, followed by a cluster of complex partial seizures (late seizures) on days 4 to 6; and radiologically by delayed reduced diffusion in the subcortical white matter (so-called bright tree appearance) on days 3 to 9 [3,4]. Excitotoxic injury with delayed (or apoptotic) neuronal death is hypothesized as a possible pathomechanism based on MRS findings showing an increase of glutamate (Glu) followed by glutamine (Gln) during the acute to subacute stages [5,6]. Mild encephalopathy associated with excitotoxicity (MEEX) shows impaired consciousness lasting for more than 24 h most often with seizures, but without a biphasic clinical course, bright tree appearance on diffusion-weighted images, hypercytokinemia, or metabolic errors [7,8]. MRS in patients with MEEX also shows acute Glu elevation followed by subacute Gln elevation (days 3 to 8) [7,8], which is identical to that observed in AESD.
Abbreviations: AESD, acute encephalopathy with biphasic seizures and late reduced diffusion; MEEX, mild encephalopathy associated with excitotoxicity; MRS, magnetic resonance spectroscopy; NAA, N-acetyl aspartate; Cr, creatine; Cho, choline; mIns, myo-inositol; Glu, glutamate; Gln, glutamine; Lac, lactate ⁎ Corresponding author at: Department of Pediatrics, Tokyo Women's Medical University Yachiyo Medical Center, 477-96 Owadashinden, Yachiyo-shi, 276-8524, Japan. E-mail address: [email protected] (J.-i. Takanashi). https://doi.org/10.1016/j.jns.2019.116636 Received 11 October 2019; Received in revised form 25 November 2019; Accepted 14 December 2019 0022-510X/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Jun-ichi Takanashi, et al., Journal of the Neurological Sciences, https://doi.org/10.1016/j.jns.2019.116636
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MRS findings in MEEX may indicate that a neurochemical process whereby the excessive Glu released from presynaptic neurons under mild excitotoxic conditions is successfully processed into Gln by astrocytes through a prompt Glu-Gln cycle, which can protect neurons from delayed death [7,8]. AESD and MEEX are, therefore, considered to constitute the excitotoxic encephalopathy spectrum. Neurological sequelae remain in approximately 70% of patients with AESD [1,2], however, it is difficult to predict the prognosis severity early in the course. We, thus, evaluated the brain metabolites in vivo observed on MRS as to whether they can predict the outcome of excitotoxic encephalopathy (AESD and MEEX), which may contribute to early therapeutic intervention and an improved neurologic outcome. 2. Materials and methods 20 Japanese patients with excitotoxic encephalopathy were hospitalized at our hospital from April 2015 to March 2019. Among them, 4 AESD patients with a neurological disorder prior to the onset of encephalopathy (2 patients with a chromosomal abnormality, one with cerebral palsy, and one with septo-optic dysplasia) were excluded. Thus, 16 previously healthy patients with excitotoxic encephalopathy (8 with AESD and 8 with MEEX) were included in this study. A diagnosis of AESD or MEEX was given based on the clinical and radiological criteria previously reported [4,8,9]. One patient with AESD [6] and 7 patients with MEEX [7,8] have been reported previously for Glu and Gln derangement on MRS. The age of the 16 patients ranged from 0.5 to 8 years old (6 patients being 0.5 to 1 year, 9 patients, 1–2 years, and one patient, 8 years). The treatment included methylprednisolone pulse therapy (15 patients), normothermia (36.0–36.5 °C, 16 patients), edaravone (5 patients), a vitamin cocktail (vitamin B1, B2, B6, and Lcarnitine for 6 patients), and anticonvulsive drugs, such as continuous intravenous infusion of midazolam (4 patients) and fosphenytoin (5 patients), based on the clinical guidelines for acute encephalopathy [9]. Neurological outcome was assessed at least after 6 months' observation using the Pediatric Cerebral Performance Category score, which has six categories: normal (score 1), mild disability (score 2), moderate disability (score 3), severe disability (score 4), coma or vegetative state (score 5), and brain death (score 6). In this study, patients with score 1 were classified as grade 1 (G1, normal), ones with scores 2 and 3 as grade 2 (G2, mild to moderate), and ones with scores 4–6 as grade 3 (G3, severe). MRS with a 3.0 T scanner (Ingenia CX 3.0 T; Philips Healthcare, Best, the Netherlands) was performed by the same method as previously reported [6], that is, point resolved spectra were obtained using TR of 5000 msec, TE of 30 msec, and NEX of 32, and acquired from the fronto-parietal white matter with a voxel size of 4.5 cm3. MRS studies were performed 35 times in total, that is, 4 times for one patient, 3 times for 3, twice for 10, and once for 2. 15 MRS studies were performed within 7 days after the onset of encephalopathy. Quantification of metabolites, including N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), myo-inositol (mIns), lactate (Lac), Glu, and Gln, was performed using an LCModel [6]. The concentration of each metabolite for aged-matched controls (0.5–1 years, 1–2 years, and 6–10 years), who were studied to evaluate disorders such as mild psychomotor retardation, headache or an enlarged head circumference, and had no identified MRI abnormality, are shown in the legend to Fig. 3. Lac was judged to be abnormal when it exceeded 1.3 mM, and for other metabolites, a value exceeding the mean ± 3SD for age-matched controls was regarded as abnormal. This study was approved by IRB of Tokyo Women's Medical University (#3535R, 3123R4).
Fig. 1. MRI in a 1-year-old female with G2 AESD on day 6 shows the bright tree appearance on diffusion-weighted image (A). MRS (B) reveals decreased NAA (4.15 mM) and Cr (3.73 mM), and increased Lac (1.40 mM) and Gln (5.35 mM) with normal Glu (5.99 mM) (B).
Fig. 2. MRS in a 2-year-old male with G1 MEEX on day 5 shows increased Gln (3.13 mM) with normal NAA (7.36 mM), Cr (4.58 mM), and Glu (6.64 mM) without a Lac peak.
G1 for 9 patients (1 AESD and 8 MEEX, 18 MRS studies, Fig. 2). Fig. 3 shows the concentrations of metabolites observed on MRS over time. NAA, Cr, Lac, and Glu are considered to be correlated with the neurological outcome. Among the 9 G1 patients, there was no obvious MRS distinction between AESD (blue squares with red margins) and MEEX (blue squares). MRS in G2 and G3 (Fig. 3-A) showed a decreased NAA concentration (less than mean-3SD, under 5.0 mM for under 1 year, under 5.6 mM for over 1 year) in 15 of 17 studies (88%), that is, 11 of 12 (92%) in G2 and 4 of 5 (80%) in G3. On the other hand, none of the 18 MRS studies in G1 (Fig. 3-B) showed such a decrease of NAA. Even in
3. Results The prognoses of the 16 patients were G3 for 2 patients (2 AESD, 5 MRS studies), G2 for 5 patients (5 AESD, 12 MRS studies, Fig. 1), and 2
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Fig. 3. The concentrations of metabolites in the brain over time in excitotoxic encephalopathy. The X and Y axes show days after onset and metabolite concentration (mmol/l). The red dotted and red lines indicate the mean-3SD metabolite concentrations at 0.5–1 and 1–2 years, respectively. A and B indicate the NAA concentrations of G2 AESD (red squares) and G3 AESD (black squares), and G1 MEEX (blue squares), and G1 AESD (blue squares with red margins), respectively. The concentrations of Cr, Lac, and Glu in G2 and 3, and G1 are shown in C and D, E and F, and G and H. Means and SD for each metabolite concentration for aged-matched controls are as follows; NAA for 0.5–1 years, 5.9 ± 0.3 (mM, mean ± SD), for 1–2 years, 6.8 ± 0.4 mM, for 6–10 years, 9.3 ± 0.4 mM; Cr for 0.5–1 years, 4.4 ± 0.2 mM, for 1–2 years, 4.7 ± 0.2 mM, for 6–10 years, 4.8 ± 0.3 mM; and Glu for 0.5–1 years, 6.1 ± 0.4 mM, for 1–2 years, 6.8 ± 0.4 mM, for 6–10 years, 5.6 ± 0.6 mM. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
The most important finding in this study is that MRS is useful for prognosis prediction as well as for the diagnosis of acute encephalopathy associated with excitotoxicity. In the acute stage within 7 days of onset, MRS data which will predict a poor neurological outcome (G2 and 3) include the following: in order of increasing sensitivity; decreased NAA (sensitivity 88%, specificity 100%), decreased Cr (sensitivity 38%, specificity 100%), and increased Lac (sensitivity 38%, specificity 100%). Poor prognostic factors throughout the course of the disease are as follows; decreased NAA (sensitivity 88%, specificity 100%), decreased Cr (sensitivity 47%, specificity 100%), increased Lac (sensitivity 47%, specificity 100%), and decreased Glu (sensitivity 35%, specificity 100%). Because the specificities for predicting a poor outcome are all 100%, if these metabolite abnormalities are observed on MRS during the course of the disease, it can be deduced that the prognosis will be poor. Because decreased NAA exhibits the highest sensitivity (88%) even in the acute stage within 7 days of onset, it will be the most effective metabolite for neurological prognosis prediction. This finding is compatible with a previous report that two AESD patients with neurological sequelae showed decreased NAA during the course of the disease [5]. NAA is synthesized in neuronal mitochondria, being almost entirely confined to neurons and their axons, thus, it is considered to be a neuron- and axon-specific marker [11]. The markedly decreased NAA observed in G2 and G3 patients may, therefore, reflect neuronal or axonal dysfunction or loss, which later results in neurological sequelae. This may also explain why NAA after the subacute stage decreases more markedly in G3 than in G2. Other metabolites that would be useful for predicting the prognosis of excitotoxic encephalopathy include decreased Cr, increased Lac, and decreased Glu. Cr observed on MRS represents the total amount of Cr and phosphocreatine present in the Cr kinase shuttle, which is related to the energy reservoir in cells with a high energy demand [11,12]. The decrease of Cr observed in G2 and G3 patients may be due to cerebral energy failure, which reasonably results in a poor neurological prognosis. Lac is the end product of glycolysis, and it increases under conditions of anaerobic glycolysis, such as in failure of energy supply [11,12]. The increased Lac observed in G2 and G3 patients may also suggest cerebral energy failure, leading to neurological sequelae. Glutamatergic neurons release Glu into the synaptic cleft, where it is taken up by surrounding astrocytes through glutamate transporters [6,13]. Glu taken up by astrocytes is amidated to a harmless compound, Gln, which is returned to the neurons for re-use as Glu, completing the Glu (in neuron)-Gln (in astrocyte) cycle [14]. MRS in patients with excitotoxic encephalopathy (AESD or MEEX) reveals acute Glu elevation within a few days of onset, which changes to subacute Gln elevation on days 4–12 [6,8], suggesting a disrupted Glu-Gln cycle due to hyperexcitotoxicity may play an important role as a pathogenic mechanism. Elevated Glu or Gln in the acute to subacute stages, which was observed in all patients in this study, however, could not predict the neurological prognosis. Conversely, decreased Glu after the subacute stage (> day 10) was a poor neuro-prognosis factor. As Glu is present in all cell types, with the largest pool in glutamatergic neurons and smaller ones in GABAergic neurons and astrocytes, neuronal dysfunction or loss reasonably results in decreased Glu, which also leads to a poor neurological prognosis. The usefulness of MRS in predicting the prognosis has also been
the acute stage within 7 days of onset, NAA in G2 and 3 was less than the mean-3SD in 7 of 8 MRS studies (88%), that is, 6/6 (100%) in G2 and 1/2 (50%) in G3, respectively. After the subacute stage (later than 7 days of onset), the NAA decrease in G3 was more prominent than that in G2. Decreased Cr concentrations (less than mean-3SD) were observed in 8 of 17 MRS studies (47%) in G2 and G3, that is, 4 of 12 (33%) in G2, and 4 of 5 (80%) in G3 (Fig. 3-C). While, none of the 18 MRS studies in G1 (Fig. 3-D) showed a decrease of the Cr concentration. In the acute stage within 7 days of onset, decreases of Cr in G2 and G3 were observed in 3/8 (38%), that is, 2/6 (33%) in G2 and 1/2 (50%) in G3, respectively. Lac concentrations over 1.3 mM (11.7 mg/dl) were observed in none of the 18 MRS studies (0%) in G1 (Fig. 3-F), and 8 of 17 (47%) in G2 and G3, that is, 4 of 12 (33%) in G2 and 4 of 5 (80%) in G3 (Fig. 3E). In the acute stage within 7 days of onset, increased Lac concentrations were seen in 3/8 (38%) in G2 and G3, that is, 2/6 (33%) in G2 and 1/2 (50%) in G3, respectively. Decreased Glu concentrations (less than mean-3SD) were observed in none of the 18 MRS studies (0%) in G1 (Fig. 3-H), and 6 of 17 (35%) in G2 and G3 (all later than 10 days) (Fig. 3-G), that is, 4 of 12 (33%) in G2, and 2 of 5 (40%) in G3. Other metabolites, Cho, mIns and Gln, seemed unable to predict the neurological prognosis. That is, increased or decreased Cho (over mean + 3SD or less than mean-3SD) was observed in 5 of 17 studies (increases and decreases being 3 and 2 each) in G2 and G3 (Supplementary Fig. A), and 5 of 18 studies (increases and decreases being 4 and 1 each) in G1 (Supplementary Fig. B). Increased or decreased mIns was observed in 3 of 17 studies (increases and decreases being 1 and 2 each) in G2 and G3 (Supplementary Fig. C), and none of 18 studies in G1 (Supplementary Fig. D). Increased Gln in the acute stage, which is the diagnostic key for the diagnosis of AESD and MEEX, was observed in all 6 patients with G2 and G3, and all 7 patients with G1 so examined (Supplementary Fig. E, F). Throughout the course of the illness, increased Gln was observed in 10/17 studies in G2 and G3, and 9/18 studies in G1. There was no correlation between treatment and prognosis (G2 and 3 versus G1): methylprednisolone pulse therapy (7/7 for G2 and 3, and 8/9 for G1), normothermia (7/7 and 9/9), edaravone (3/7 and 2/9, p = .37 [Fisher's exact test]), a vitamin cocktail (2/7 and 4/9, p = .45), continuous intravenous infusion of midazolam (2/7 and 2/9, p = .61), and fosphenytoin (3/7 and 2/9, p = .37).
4. Discussion MRI is usually performed early for children with suspected encephalopathy to detect characteristic lesions of encephalopathy syndromes, such as the bright tree appearance in AESD, a splenial lesion in clinically mild encephalitis/encephalopathy with a reversible splenial lesion, and bilateral thalamic lesions in acute necrotizing encephalopathy [2–4]. MRS performed at the same time as MRI will contribute to the diagnosis of excitotoxic encephalopathy through the detection of elevated Glu or Gln [5–8]. If MRS in the acute stage is also able to predict the neurological prognosis, it may change the treatment strategy, leading to aggressive therapeutic intervention such as hypothermia [10]. 4
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References
reported in patients with hypoxic-ischemic encephalopathy [12]. Cerebral injury secondary to hypoxic-ischemic encephalopathy disrupts mitochondrial ATP synthesis, leading to neuronal depolarization inducing Glu release, resulting in delayed neuronal cell death [15], which is also postulated in excitotoxic encephalopathy. MRS findings related to a poor neurological prognosis in patients with hypoxic-ischemic encephalopathy include decreases of NAA and Cr, and an increase of Lac [12], which are consistent with those in excitotoxic encephalopathy observed in this study. The same prognostic factors on MRS in both conditions associated with excitotoxicity may indicate that the results of this study are reasonable and reliable. From the viewpoints of clinical symptoms and laboratory findings, a few reports proposed prognostic factors for AESD. They included prolonged seizures at the onset and loss of consciousness 24 h after the onset [16], coma and involuntary movements before the late seizures, high levels of serum alanine aminotransferase, more extensive lesions of the cerebrum and basal ganglia [17], and coma 12–24 h after the onset and elevation of serum creatinine and alanine aminotransferase [18]. By combining the previously presented poor prognostic factors and MRS findings in this study, it will be possible to obtain a more accurate prognosis of excitotoxic encephalopathy. The limitation of this study is the small number of patients from one hospital; because we had to treat all patients without any evidencebased protocol, the timing or combination of therapies for encephalopathy was not uniform. MRS, which is essential for the diagnosis of MEEX, is not always possible in Japanese hospitals. Because the concentrations of metabolites observed on MRS depend on the MR manufacturer, magnetic field strength and measurement sequences, agematched control metabolite concentration data is necessary for each institution to apply the MRS results of this study. In conclusion, MRS data which will predict a poor neurological outcome include decreased NAA, decreased Cr, increased Lac, and decreased Glu. MRS is useful for prognosis prediction of acute excitotoxic encephalopathy as well as for a diagnosis, and may contribute to early therapeutic intervention and an improved neurologic outcome. Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jns.2019.116636.
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Acknowledgement This study was in part supported by JSPS KAKENHI Grant Number JP19K08237, Ministry of Health, Labor and Welfare, Grant-in-Aid for Research on Measures for Intractable Diseases (H30-Nanji-Ippan-007), and AMED, Practical Research Project for Rare/Intractable Diseases (19ek0109270). Declaration of Competing Interest All authors declare no conflicts of interest.
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