Magnetic resonance spectroscopy in patients with MELAS

Magnetic resonance spectroscopy in MELAS syndrome: correlation with CSF and plasma metabolite levels and change after glutamine supplementation

PURPOSE

MELAS syndrome is a genetic disorder caused by mitochondrial DNA mutations. We previously described that MELAS patients had increased CSF glutamate and decreased CSF glutamine levels and that oral glutamine supplementation restores these values. Proton magnetic resonance spectroscopy (1H-MRS) allows the in vivo evaluation of brain metabolism. We aimed to compare 1H-MRS of MELAS patients with controls, the 1H-MRS after glutamine supplementation in the MELAS group, and investigate the association between 1H-MRS and CSF lactate, glutamate, and glutamine levels.

METHODS

We conducted an observational case-control study and an open-label, single-cohort study with single-voxel MRS (TE 144/35 ms). We assessed the brain metabolism changes in the prefrontal (PFC) and parieto-occipital) cortex (POC) after oral glutamine supplementation in MELAS patients. MR spectra were analyzed with jMRUI software.

RESULTS

Nine patients with MELAS syndrome (35.8 ± 3.2 years) and nine sex- and age-matched controls were recruited. Lactate/creatine levels were increased in MELAS patients in both PFC and POC (0.40 ± 0.05 vs. 0, p < 0.001; 0.32 ± 0.03 vs. 0, p < 0.001, respectively). No differences were observed between groups in glutamate and glutamine (Glx/creatine), either in PFC (p = 0.930) or POC (p = 0.310). No differences were observed after glutamine supplementation. A positive correlation was found between CSF lactate and lactate/creatine only in POC (0.85, p = 0.003).

CONCLUSION

No significant metabolite changes were observed in the brains of MELAS patients after glutamine supplementation. While we found a positive correlation between lactate levels in CSF and 1H-MRS in MELAS patients, we could not monitor treatment response over short periods with this tool.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04948138; initial release 24/06/2021; first patient enrolled on 1/07/2021. https://clinicaltrials.gov/ct2/show/NCT04948138.

Glutamine metabolism in diseases associated with mitochondrial dysfunction

Mitochondrial dysfunction can arise from genetic defects or environmental exposures and impact a wide range of biological processes. Among these are metabolic pathways involved in glutamine catabolism, anabolism, and glutamine-glutamate cycling. In recent years, altered glutamine metabolism has been found to play important roles in the pathologic consequences of mitochondrial dysfunction. Glutamine is a pleiotropic molecule, not only providing an alternate carbon source to glucose in certain conditions, but also playing unique roles in cellular communication in neurons and astrocytes. Glutamine consumption and catabolic flux can be significantly altered in settings of genetic mitochondrial defects or exposure to mitochondrial toxins, and alterations to glutamine metabolism appears to play a particularly significant role in neurodegenerative diseases. These include primary mitochondrial diseases like Leigh syndrome (subacute necrotizing encephalopathy) and MELAS (mitochondrial myopathy with encephalopathy, lactic acidosis, and stroke-like episodes), as well as complex age-related neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Pharmacologic interventions targeting glutamine metabolizing and catabolizing pathways appear to provide some benefits in cell and animal models of these diseases, indicating glutamine metabolism may be a clinically relevant target. In this review, we discuss glutamine metabolism, mitochondrial disease, the impact of mitochondrial dysfunction on glutamine metabolic processes, glutamine in neurodegeneration, and candidate targets for therapeutic intervention.

Visual memory failure presages conversion to MELAS phenotype

OBJECTIVE

To examine the correlation between verbal and visual memory function and correlation with brain metabolites (lactate and N-Acetylaspartate, NAA) in individuals with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS).

METHODS

Memory performance and brain metabolites (ventricular lactate, occipital lactate, and occipital NAA) were examined in 18 MELAS, 58 m.3243A > G carriers, and 20 familial controls. Measures included the Selective Reminding Test (verbal memory), Benton Visuospatial Retention Test (visual memory), and MR Spectroscopy (NAA, Lactate). ANOVA, chi-squared/Fisher's exact tests, paired t-tests, Pearson correlations, and Spearman correlations were used.

RESULTS

When compared to carriers and controls, MELAS patients had the: (1) most impaired memory functions (Visual: p = 0.0003; Verbal: p = 0.02), (2) greatest visual than verbal memory impairment, (3) highest brain lactate levels (p < 0.0001), and (4) lowest brain NAA levels (p = 0.0003). Occipital and ventricular lactate to NAA ratios correlated significantly with visual memory performance (p ≤ 0.001). Higher lactate levels (p ≤ 0.01) and lower NAA levels (p = 0.0009) correlated specifically with greater visual memory dysfunction in MELAS. There was little or no correlation with verbal memory.

INTERPRETATION

Individuals with MELAS are at increased risk for impaired memory. Although verbal and visual memory are both affected, visual memory is preferentially affected and more clearly associated with brain metabolite levels. Preferential involvement of posterior brain regions is a distinctive clinical signature of MELAS. We now report a distinctive cognitive phenotype that targets visual memory more prominently and earlier than verbal memory. We speculate that this finding in carriers presages a conversion to the MELAS phenotype.

MRI Features of Stroke-Like Episodes in Mitochondrial Encephalomyopathy With Lactic Acidosis and Stroke-Like Episodes

Mitochondrial myopathy encephalopathy lactic acidosis and stroke-like episodes (MELAS) is an important cause of stroke-mimicking diseases that predominantly affect patients before 40 years of age. MELAS results from gene mutations in either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) responsible for the wide spectrum of clinical symptoms and imaging findings. Neurological manifestations can present with stroke-like episodes (the cardinal features of MELAS), epilepsy, cognitive and mental disorders, or recurrent headaches. Magnetic resonance imaging (MRI) is an important tool for detecting stroke-like lesions, accurate recognition of imaging findings is important in guiding clinical decision making in MELAS patients. With the development of neuroimaging technologies, MRI plays an increasingly important role in course monitoring and efficacy assessment of the disease. In this article, we provide an overview of the neuroimaging features and the application of novel MRI techniques in MELAS syndrome.

Impaired aerobic capacity and premature fatigue preceding muscle weakness in the skeletal muscle Tfam-knockout mouse model

Mitochondrial diseases are genetic disorders that lead to impaired mitochondrial function, resulting in exercise intolerance and muscle weakness. In patients, muscle fatigue due to defects in mitochondrial oxidative capacities commonly precedes muscle weakness. In mice, deletion of the fast-twitch skeletal muscle-specific Tfam gene (Tfam KO) leads to a deficit in respiratory chain activity, severe muscle weakness and early death. Here, we performed a time-course study of mitochondrial and muscular dysfunctions in 11- and 14-week-old Tfam KO mice, i.e. before and when mice are about to enter the terminal stage, respectively. Although force in the unfatigued state was reduced in Tfam KO mice compared to control littermates (wild type) only at 14 weeks, during repeated submaximal contractions fatigue was faster at both ages. During fatiguing stimulation, total phosphocreatine breakdown was larger in Tfam KO muscle than in wild-type muscle at both ages, whereas phosphocreatine consumption was faster only at 14 weeks. In conclusion, the Tfam KO mouse model represents a reliable model of lethal mitochondrial myopathy in which impaired mitochondrial energy production and premature fatigue occur before muscle weakness and early death.

Summary: A time-course study of mitochondrial and muscular dysfunctions in a mouse model of mitochondrial myopathy reveals that decreased resistance to fatigue together with decreased oxidative capacities arise ahead of muscle weakness.

Brain MRS correlates with mitochondrial dysfunction biomarkers in MELAS-associated mtDNA mutations

Objective

The purpose of this study was to investigate correlations between brain proton magnetic resonance spectroscopy (¹H‐MRS) findings with serum biomarkers and heteroplasmy of mitochondrial DNA (mtDNA) mutations. This study enrolled patients carrying mtDNA mutations associated with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke‐like episodes (MELAS), and MELAS‐Spectrum Syndrome (MSS).

Methods

Consecutive patients carrying mtDNA mutations associated with MELAS and MSS were recruited and their serum concentrations of lactate, alanine, and heteroplasmic mtDNA mutant load were evaluated. The brain protocol included single‐voxel ¹H‐MRS (1.5T) in the medial parieto‐occipital cortex (MPOC), left cerebellar hemisphere, parieto‐occipital white matter (POWM), and lateral ventricles. Relative metabolite concentrations of N‐acetyl‐aspartate (NAA), choline (Cho), and myo‐inositol (mI) were estimated relative to creatine (Cr), using LCModel 6.3.

Results

Six patients with MELAS (age 28 ± 13 years, 3 [50%] female) and 17 with MSS (age 45 ± 11 years, 7 [41%] female) and 39 sex‐ and age‐matched healthy controls (HC) were enrolled. These patients demonstrated a lower NAA/Cr ratio in MPOC compared to HC (p = 0.006), which inversely correlated with serum lactate (p = 0.021, rho = −0.68) and muscle mtDNA heteroplasmy (p < 0.001, rho = −0.80). Similarly, in the cerebellum patients had lower NAA/Cr (p < 0.001), Cho/Cr (p = 0.002), and NAA/mI (p = 0.001) ratios, which negatively correlated with mtDNA blood heteroplasmy (p = 0.001, rho = −0.81) and with alanine (p = 0.050, rho = −0.67). Ventricular lactate was present in 78.3% (18/23) of patients, correlating with serum lactate (p = 0.024, rho = 0.58).

Conclusion

Correlations were found between the peripheral and biochemical markers of mitochondrial dysfunction and brain in vivo markers of neurodegeneration, supporting the use of both biomarkers as signatures of MELAS and MSS disease, to evaluate the efficacy of potential treatments.

Clinical Insights into Mitochondrial Neurodevelopmental and Neurodegenerative Disorders: Their Biosignatures from Mass Spectrometry-Based Metabolomics

Mitochondria are dynamic multitask organelles that function as hubs for many metabolic pathways. They produce most ATP via the oxidative phosphorylation pathway, a critical pathway that the brain relies on its energy need associated with its numerous functions, such as synaptic homeostasis and plasticity. Therefore, mitochondrial dysfunction is a prevalent pathological hallmark of many neurodevelopmental and neurodegenerative disorders resulting in altered neurometabolic coupling. With the advent of mass spectrometry (MS) technology, MS-based metabolomics provides an emerging mechanistic understanding of their global and dynamic metabolic signatures. In this review, we discuss the pathogenetic causes of mitochondrial metabolic disorders and the recent MS-based metabolomic advances on their metabolomic remodeling. We conclude by exploring the MS-based metabolomic functional insights into their biosignatures to improve diagnostic platforms, stratify patients, and design novel targeted therapeutic strategies.

Acute Cortical Lesions in MELAS Syndrome: Anatomic Distribution, Symmetry, and Evolution

BACKGROUND AND PURPOSE

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a rare mitochondrial disorder affecting children and young adults. Stroke-like episodes are often associated with acute cortical lesions in the posterior cerebral cortex and are classically described as asymmetric and transient. In this study we assessed the anatomic distribution of acute cortical lesions, the incidence of symmetry, and the temporal evolution of lesions.

MATERIALS AND METHODS

This was a retrospective cohort study of patients who had a confirmed genetic diagnosis of a pathogenic variant associated with MELAS and MR imaging performed at our center (2006-2018). Each MR imaging study was assessed for new lesions using T1, T2, FLAIR, DWI, ADC, and SWI. The anatomic location, symmetry, and temporal evolution of lesions were analyzed.

RESULTS

Eight patients with the same pathogenic variant of MELAS (MT-TL1 m.3243A>G) with 31 MR imaging studies were included. Forty-one new lesions were identified in 17 of the studies (5 deep, 36 cortical). Cortical lesions most commonly affected the primary visual cortex, the middle-third of the primary somatosensory cortex, and the primary auditory cortex. Thirty of 36 cortical lesions had acute cortical diffusion restriction, of which 21 developed cortical laminar necrosis on subacute imaging. Six of 11 studies with multiple lesions showed symmetric cortical involvement.

CONCLUSIONS

Acute cortical lesions in MELAS most commonly affect the primary visual, somatosensory, and auditory cortices, all regions of high neuronal density and metabolic demand. The most common pattern of temporal evolution is acute cortical diffusion restriction with subacute cortical laminar necrosis and chronic volume loss. Symmetric involvement is more common than previously described.

MELAS: Monitoring treatment with magnetic resonance spectroscopy

BACKGROUND

To assess the utility of Magnetic Resonance Spectroscopy (MRS) as a biomarker of response to L-arginine in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS).

AIMS

To describe a case of MELAS treated with L-arginine that showed improvement clinically and on serial MRS METHODS: MRS was performed on a 1.5-Tesla scanner to evaluate a MELAS patient before, during, and after intravenous (IV) L-arginine therapy for the treatment of stroke-like episodes. L-arginine was infused at a dose of 500 mg/kg daily for 7 days followed by oral arginine therapy.

RESULTS

The patient had clinical improvement after treatment with IV L-arginine. MRS performed before, during, and after treatment with IV L-arginine showed significant improvement in brain lactate and increase in the N-acetylaspartate/Choline (NAA/Cho) ratio compared to pre-treatment baseline.

CONCLUSION

Serial MRS imaging showed significant improvement in lactate peaks and NAA/Cho ratios that corresponded with clinical improvement after L-arginine therapy. Given this correlation between radiologic and clinical improvement, MRS may be a useful biomarker assessing response to treatment in MELAS.

A new approach to Z-spectrum acquisition: prospective baseline enhancement (PROBE) for CEST/Nuclear Overhauser Effect

PURPOSE

To develop a prospective baseline enhancement that compensates for intermingled background effects in Z-spectra to achieve sensitivity enhancement of peaks related to CEST and nuclear Overhauser effect.

METHODS

An MRI sequence-specific compensation of background effects is achieved through variation of the pulsed saturation power, ω 1 , max , with the chemical shift, δ . After a "scout acquisition" of a standard Z-spectrum, the background is modeled through an appropriate spin system. Subsequently, an optimization procedure yields ω 1 , m a x ( δ ) values that compensate for background contributions yielding a flat baseline. Contributions from metabolites not considered in the optimization procedure are enhanced as distinct perturbations to the baseline. For experimental verification, mapping of the lactate concentration in the presence of cross-linked bovine serum albumin was performed in phantoms at 7 T. As proof of concept, explorative experiments were performed in healthy human subjects at 3 T.

RESULTS

Nuisance contributions from direct water saturation, macromolecular magnetization transfer, and exchanging background protons were successfully removed from the Z-spectrum in phantoms and in brain tissue. The lactate methyl, methine, and hydroxyl peaks were readily observable in vitro. The peak areas correlated linearly with known concentrations. Improvement of the detection limit was achieved by a sparse distribution of saturation frequencies, allowing for more efficient signal averaging.

CONCLUSION

An optimization framework for high-resolution metabolite mapping by means of CEST/nuclear Overhauser effect was developed. It offers full flexibility to select spin-pool moieties, whose influence on the Z-spectrum will be compensated. Deviations from this background model will provide a contrast at the respective offset frequencies.

Correlation of Serum Biomarkers and Magnetic Resonance Spectroscopy in Monitoring Disease Progression in Patients With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes Due to mtDNA A3243G Mutation

Background: Analysis of serum biomarkers and magnetic resonance spectroscopy (MRS) are useful for monitoring disease progression in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). We evaluated the correlation of serum biomarkers and MRS parameters during changes associated with stroke-like episodes. Methods: In 13 symptomatic MELAS patients carrying the A3243G mutation, we retrospectively obtained 207 voxels from 41 MRS studies, which were divided into three groups according to the temporal association with stroke-like episodes. The MRS NAA/Cr, Cho/Cr, NAA/Cho ratios, the presence of a lactate peak, serum biomarkers, serum lactate level and the pyruvate (Lac/Pyr) ratio were determined. Results: In regions with acute infarcts, the severity of serum Lac/Pyr and that of the MRS lactate peak (P = 0.0007) correlated; serum lactate (P = 0.02), severity of elevated serum lactate (P = 0.04), and serum Lac/Pyr (P = 0.02) correlated weakly. In previously infarcted regions, the severity of the MRS lactate peak and serum Lac/Pyr (P = 0.03), as well as the severity of serum Lac/Pyr (P = 0.02) were weakly correlated. In structurally normal regions, we found a weak to moderate negative correlation between serum lactate and MRS NAA/Cr (P = 0.008), and between the severity of elevated serum lactate and MRS NAA/Cr (P = 0.002) as well as MRS NAA/Cho (P = 0.02). Conclusions: MRS parameters correlate with specific serum biomarkers, and are useful for monitoring changes in brain metabolites, particularly as related to stroke-like episodes.

Mitochondrial dysfunction and cerebral metabolic abnormalities in patients with mitochondrial encephalomyopathy subtypes: Evidence from proton MR spectroscopy and muscle biopsy

AIMS

Accumulated evidence indicates that cerebral metabolic features, evaluated by proton magnetic resonance spectroscopy (¹ H-MRS), are sensitive to early mitochondrion dysfunction associated with mitochondrial encephalomyopathy (ME). The metabolite ratios of lactate (lac)/Cr, N-acetyl aspartate (NAA)/creatine (Cr), total choline (tCho)/Cr, and myoinositol (mI)/Cr are measured in the infarct-like lesions by ¹ H-MRS and may reveal metabolic changes associated with ME. However, the application of this molecular imaging technique in the investigation of the pathology of ME subtypes is unknown.

METHODS

In this study, cerebral metabolic features of pathologically diagnosed ME cases, that is, 19 mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS); nine chronic progressive external ophthalmoplegia (CPEO); and 23 healthy controls, were investigated using ¹ H-MRS. Receiver operating characteristics (ROC) analysis was used to evaluate the diagnostic power of the cerebral metabolites. Histochemical evaluation was carried out on muscle tissues derived from biopsy to assess the abnormal mitochondrial proliferation. The association between cerebral metabolic and mitochondrial cytopathy was examined by correlation analysis.

RESULTS

Patients with MELAS or CPEO exhibited a significantly higher Lac/Cr ratio and a lower NAA/Cr ratio compared with controls. The ROC curve of Lac/Cr ratio indicated prominent discrimination between MELAS or CPEO and healthy control subjects, whereas the NAA/Cr ratio may present diagnostic power in the distinction of MELAS from CPEO. Lower NAA/Cr ratio was associated with higher Lac/Cr in MELAS, but not in CPEO. Furthermore, higher ragged-red fibers (RRFs) percentages were associated with elevated Lac/Cr and reduced NAA/Cr ratios, notably in MELAS. This association was not noted in the case of mI/Cr ratio.

CONCLUSIONS

Mitochondrial cytopathy (lactic acidosis and RRFs on muscle biopsy) was associated with neuronal viability but not glial proliferation, notably in MELAS. Mitochondrial neuronopathy and neuronal vulnerability are considered significant causes in the pathogenesis of MELAS, particularly with regard to stroke-like episodes.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Type 2 diabetes mellitus: a potentially modifiable risk factor for neurochemical brain changes in bipolar disorders

BACKGROUND

Neuroimaging changes in bipolar disorder (BD) may be secondary to the presence of certain clinical factors. Type 2 diabetes mellitus (T2DM) damages the brain and frequently co-occurs with BD. Studying patients with both T2DM and BD could help identify preventable risk factors for neuroimaging changes in BD.

METHODS

We used 1.5T magnetic resonance spectroscopy to measure prefrontal N-acetylaspartate (NAA), which is mainly localized in neurons, and total creatine (tCr), an energy metabolite, in 19 BD patients with insulin resistance/glucose intolerance (BD + IR/GI), 14 BD subjects with T2DM (BD + T2DM), 15 euglycemic BD participants, and 11 euglycemic, nonpsychiatric control.

RESULTS

The levels of NAA and tCr were lowest among BD + T2DM, intermediate in the BD + IR/GI, and highest among the euglycemic BD and control subjects (F₃,₅₅ = 4.57, p = .006; F₃,₅₅ = 2.92, p = .04, respectively). Even the BD + IR/GI subjects had lower NAA than the euglycemic participants (t₄₃ = 2.13, p = .04). Total Cr was associated with NAA (β = .52, t₅₆ = 5.57, p = .000001). Both NAA and tCr correlated with Global Assessment of Functioning scores (r₄₆ = .28, p = .05; r₄₆ = .48, p = .0004, respectively).

CONCLUSIONS

T2DM, but also prediabetes, may be risk factors for prefrontal neurochemical alterations in BD. These changes were associated with poor psychosocial functioning and could indicate impaired energy metabolism. The findings emphasize the importance of improving diabetes care in BD and suggest potential options for treatment of neuroimaging alterations.

High cytochrome c oxidase expression links to severe skeletal energy failure by (31)P-MRS spectroscopy in mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

AIMS

The purpose of this study was to evaluate the energy metabolism and mitochondrial function in skeletal muscle from patients with Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) or chronic progressive external ophthalmoplegia (CPEO) using phosphorus magnetic resonance spectroscopy ((31)P-MRS), to determine whether abnormally increasing cytochrome c oxidase (COX), as detected in muscle biopsy, could be a cause for MELAS.

METHODS

(31)P-MRS was performed on the quadriceps femoris muscle of 12 healthy volunteers and 11 patients diagnosed as MELAS or CPEO by muscle biopsy and genetic analysis. All subjects experienced a state of rest, 5-min exercise, and 5-min recovery protocol in a supine position.

RESULTS

Compared to CPEO, MELAS patients typically exhibited COX-positive ragged-red fibers (RRFs) as well as strongly SDH-positive blood vessels (SSVs). However, based on (31)P-MRS results, MELAS showed a higher inorganic phosphate (Pi)/phosphocreatine (PCr) ratio and lower ATP/PCr ratio during exercise and delayed Pi/PCr and ATP/PCr recovery to normal.

CONCLUSIONS

This study suggests that high COX expression contributes to severe skeletal energy failure by (31)P-MRS spectroscopy in MELAS.

Cerebral metabolic abnormalities in A3243G mitochondrial DNA mutation carriers

OBJECTIVE

To establish cerebral metabolic features associated with the A3243G mitochondrial DNA mutation with proton magnetic resonance spectroscopic imaging ((1)H MRSI) and to assess their potential as prognostic biomarkers.

METHODS

In this prospective cohort study, we investigated 135 clinically heterogeneous A3243G mutation carriers and 30 healthy volunteers (HVs) with (1)H MRSI. Mutation carriers included 45 patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS); 11 participants who would develop the MELAS syndrome during follow-up (converters); and 79 participants who would not develop the MELAS syndrome during follow-up (nonconverters). The groups were compared with respect to MRSI metabolic indices of 1) anaerobic energy metabolism (lactate), 2) neuronal integrity (N-acetyl-l-aspartate [NAA]), 3) mitochondrial function (NAA; lactate), 4) cell energetics (total creatine), and 5) membrane biosynthesis and turnover (total choline [tCho]).

RESULTS

Consistent with prior studies, the patients with MELAS had higher lactate (p < 0.001) and lower NAA levels (p = 0.01) than HVs. Unexpectedly, converters showed higher NAA (p = 0.042), tCho (p = 0.004), and total creatine (p = 0.002), in addition to higher lactate levels (p = 0.032), compared with HVs. Compared with nonconverters, converters had higher tCho (p = 0.015). Clinically, converters and nonconverters did not differ at baseline. Lactate and tCho levels were reliable biomarkers for predicting the risk of individual mutation carriers to develop the MELAS phenotype.

CONCLUSIONS

(1)H MRSI assessment of cerebral metabolism in A3243G mutation carriers shows promise in identifying disease biomarkers as well as individuals at risk of developing the MELAS phenotype.

Transient ischemic attack-like episodes without stroke-like lesions in MELAS

A stroke-like episode is a core symptom in mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). Proton magnetic resonance spectroscopy (1H-MRS) is useful in the diagnosis of mitochondrial diseases. We report an 8-year-old girl with MELAS, presenting with a seizure and blindness. 1H-MRS showed a strikingly elevated lactate peak in the right occipital region, where no abnormal signals appeared on either T2-W or diffusion-weighted MRI. She recovered completely within a day. We describe this mild clinical condition with abnormal lactate peak in normal-appearing gray matter as a transient ischemic attack-like episode in MELAS.

Metabolite measurements in the caudate nucleus, anterior cingulate cortex and hippocampus among patients with mitochondrial disorders: a case-control study using proton magnetic resonance spectroscopy

BACKGROUND

Mitochondrial disorders are clinical syndromes associated with mutations in the mitochondrial or nuclear genome that result in impaired oxidative phosphorylation and deficient energy production. Metabolic abnormalities in brain areas associated with cognitive functions could give rise to neuropsychiatric symptomatology. The aim of this study was to use single-voxel proton magnetic resonance spectroscopy to identify metabolic abnormalities in regions implicated in neuropsychiatric symptoms in patients with mitochondrial disorders.

METHODS

N-acetyl-aspartate and creatine levels were measured in the caudate nucleus, anterior cingulate cortex and hippocampus in 15 patients with mitochondrial disorders compared with 15 healthy controls matched for age and sex.

RESULTS

N-acetyl-aspartate levels were significantly lower in the caudate nucleus among patients with mitochondrial disorders (mean 7.04 ± 1.19 standard deviation [SD] institutional units) compared with healthy controls (mean 8.19 ± 1.18 SD institutional units; p = 0.02). Creatine levels were lower in the caudate nucleus among patients compared with controls (patients: mean 6.84 ± 1.42 SD institutional units; controls: mean 7.52 ± 0.76 SD institutional units; p = 0.03), but the results were no longer significant after correction for multiple comparisons. There were no significant differences in metabolite measurements between patients and controls in the anterior cingulate cortex and the hippocampus.

INTERPRETATION

Metabolic abnormalities were identified exclusively in the caudate nucleus, with significantly lower N-acetyl-aspartate levels among patients compared with controls. These results suggest that the corpus striatum may be highly susceptible to mitochondrial oxidative phosphorylation defects and resultant cell loss. Given the role of the caudate nucleus in cognitive and executive functions, our findings raise the possibility that metabolic abnormalities in the caudate nucleus may contribute to cognitive impairment and neuropsychiatric symptoms in patients with mitochondrial disorders, which could be investigated in future studies.

Brain uptake of Tc99m-HMPAO correlates with clinical response to the novel redox modulating agent EPI-743 in patients with mitochondrial disease

While decreased ATP production and redox imbalance are central to mitochondrial disease pathogenesis, efforts to develop effective treatments have been hampered by the lack of imaging markers of oxidative stress. In this study we wished to determine if Tc99m-HMPAO, a SPECT imaging marker of cerebral blood flow and glutathione/protein thiol content, could be used to monitor the effect(s) of EPI-743, an oral redox modulating, para-benzoquinone based therapeutic for mitochondrial disease. We hypothesized that treatment changes in HMPAO uptake would be inversely proportional to changes in oxidative stress within the brain and directly correlate to clinical response to EPI-743 therapy. Twenty-two patients with mitochondrial disease were treated with EPI-743. Each underwent baseline and 3-month Tc99m-HMPAO SPECT scanning along with clinical/neurologic evaluations. Diseases treated were: Leigh syndrome (n=7), polymerase γ deficiency (n=5), MELAS (n=5), Friedreich ataxia (n=2), Kearns-Sayre syndrome, Pearson syndrome, and mtDNA depletion syndrome. Neuro-anatomic uptake analyses of HMPAO were performed with NeuroGam™ (Segami Corp.) statistical software and clinical response was assessed by the Newcastle Paediatric Mitochondrial Disease Scale or Newcastle Mitochondrial Disease Adult Scale depending on patient age. For all 22 patients there was a significant linear correlation between the change in cerebellar uptake of HMPAO and the improvement in Newcastle score (r=0.623, **p=0.00161). The MELAS subgroup showed a significant relationship of whole brain uptake (n=5, r=0.917, *p=0.028) to improvement in Newcastle score. We conclude that Tc99m-HMPAO SPECT scanning has promise as a general marker of the oxidative state of the brain and its response to redox modulating therapies. Further studies will be needed to confirm these findings in a more homogenous study population.

Proton magnetic resonance spectroscopy and MRI reveal no evidence for brain mitochondrial dysfunction in children with autism spectrum disorder

Brain mitochondrial dysfunction has been proposed as an etiologic factor in autism spectrum disorder (ASD). Proton magnetic resonance spectroscopic imaging ((1)HMRS) and MRI were used to assess for evidence of brain mitochondrial dysfunction in longitudinal samples of children with ASD or developmental delay (DD), and cross-sectionally in typically developing (TD) children at 3-4, 6-7 and 9-10 years-of-age. A total of 239 studies from 130 unique participants (54ASD, 22DD, 54TD) were acquired. (1)HMRS and MRI revealed no evidence for brain mitochondrial dysfunction in the children with ASD. Findings do not support a substantive role for brain mitochondrial abnormalities in the etiology or symptom expression of ASD, nor the widespread use of hyperbaric oxygen treatment that has been advocated on the basis of this proposed relationship.

Tissue-specific splicing of an Ndufs6 gene-trap insertion generates a mitochondrial complex I deficiency-specific cardiomyopathy

Mitochondrial complex I (CI) deficiency is the most common mitochondrial enzyme defect in humans. Treatment of mitochondrial disorders is currently inadequate, emphasizing the need for experimental models. In humans, mutations in the NDUFS6 gene, encoding a CI subunit, cause severe CI deficiency and neonatal death. In this study, we generated a CI-deficient mouse model by knockdown of the Ndufs6 gene using a gene-trap embryonic stem cell line. Ndufs6(gt/gt) mice have essentially complete knockout of the Ndufs6 subunit in heart, resulting in marked CI deficiency. Small amounts of wild-type Ndufs6 mRNA are present in other tissues, apparently due to tissue-specific mRNA splicing, resulting in milder CI defects. Ndufs6(gt/gt) mice are born healthy, attain normal weight and maturity, and are fertile. However, after 4 mo in males and 8 mo in females, Ndufs6(gt/gt) mice are at increased risk of cardiac failure and death. Before overt heart failure, Ndufs6(gt/gt) hearts show decreased ATP synthesis, accumulation of hydroxyacylcarnitine, but not reactive oxygen species (ROS). Ndufs6(gt/gt) mice develop biventricular enlargement by 1 mo, most pronounced in males, with scattered fibrosis and abnormal mitochondrial but normal myofibrillar ultrastructure. Ndufs6(gt/gt) isolated working heart preparations show markedly reduced left ventricular systolic function, cardiac output, and functional work capacity. This reduced energetic and functional capacity is consistent with a known susceptibility of individuals with mitochondrial cardiomyopathy to metabolic crises precipitated by stresses. This model of CI deficiency will facilitate studies of pathogenesis, modifier genes, and testing of therapeutic approaches.

Proton MR Spectroscopy in Patients with Leigh Syndrome

The aim of the present study was to evaluate MRS findings in patients with Leigh syndrome. We report our results of HMR spectroscopic studies performed in six patients (aged four months to ten years) with clinically proved Leigh syndrome. All examinations were done with 1.5 T scanner using an eight-channel phased array head coil. HMRS data were obtained using 2D-chemical shift imaging (CSI) and SVS sequences with short (30 ms) and long (135 ms) echo time. The MR spectra were acquired in multiple voxel localized in deep gray matter and periventricular white matter. The results were compared to the control group data. In most of our patients we found bilateral lesions in the basal ganglia and brain stem. HMRS data revealed elevated lactate in the affected areas, significantly diminished NAA/Cr ratio. The relatively high Cho/Cr ratio in the gray and white matter was also noted. HMRS is an important tool for non-invasive brain tissue analysis in Leigh syndrome.

Neuroimaging of stroke-like episodes in MELAS

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) shows sudden neurological deficits that are called 'stroke-like episodes'. With regard to the pathophysiology of stroke-like episodes, so-called mitochondrial angiopathy and cytopathy theories have been proposed, but the subject is still controversial. To clarify this matter and to contribute to the development of a treatment for MELAS, we review here current neuroimaging research and consider the pathophysiology of stroke-like lesions. With regard to diffusion-weighted imaging findings, early reports often showed an elevated apparent diffusion coefficient (ADC) in stroke-like lesions; this was considered to be mainly vasogenic edema in the acute phase and is a different pattern than that in stroke. However, there has recently been an increase in the number of reports of a decrease in ADC; these cases are considered to be cytotoxic edema in the acute phase, which is compatible with stroke. With regard to (1)H-magnetic resonance spectroscopy findings in stroke-like lesions, a decrease in N-acetylaspartate and an increase in lactate have been reported. With regard to single photon emission computed tomography findings for stroke-like lesions in MELAS, an overall trend is hyperperfusion in the acute stage (within 1 month) of stroke-like episodes and hypoperfusion in the chronic stage (several months later). With regard to positron emission tomography, nearly all of these reports are consistent with the mitochondrial cytopathy theory. With regard to neuropathology in MELAS, the most common findings during the chronic stage of stroke-like episodes include foci of necrosis and peculiar vascular changes (abnormalities of mitochondria in small arteries). Concerning the pathology of the acute stage of stroke-like episodes, extensive petechial hemorrhage along the gyri of the cortex corresponding to acute stroke-like lesions has been reported. To clarify the true pathophysiology of stroke-like episodes, we offer three suggestions. First, we must define the precise onset of stroke-like episodes. Second, current studies are limited by the difficulty of imaging just before and just after (within a few minutes) the onset of stroke-like episodes. Third, we hope to establish an experimental animal model. We should conduct a simultaneous multimodal imaging and histological study just before and just after (within a few minutes) the onset of stroke-like episodes in an experimental animal model.

31P-MRS demonstrates a reduction in high-energy phosphates in the occipital lobe of migraine without aura patients

BACKGROUND

Differences in brain energy metabolism have been found between migraine patients and controls in previous phosphorus magnetic resonance spectroscopy ((31)P-MRS) studies, most of them emphasizing migraine with aura (MwA). The aim of this study was to verify potential changes in resting-state brain energy metabolism in patients with migraine without aura (MwoA) compared to control subjects by (31)P-MRS at 3 tesla.

METHODS

Quantification was performed using the phantom replacement technique. MRS measurements were performed interictally and in the medial occipital lobe of 19 MwoA patients and 26 age-matched controls.

RESULTS

A significantly decreased phosphocreatine concentration ([PCr]) was found as in previous studies. While adenosine triphosphate concentration ([ATP]) was considered to be constant in previously published work, this study found a significant decrease in the measured [ATP] in MwoA patients. The inorganic phosphate ([P(i)]) and magnesium ([Mg(2+)]) concentrations were not significantly different between MwoA patients and controls.

CONCLUSIONS

The altered metabolic concentrations indicate that the energy metabolism in MwoA patients is impaired, certainly in a subgroup of patients. The actual decrease in [ATP] adds further strength to the theory of the presence of a mitochondrial component in the pathophysiology of migraine.

The appearance of ADCs in the non-affected areas of the patients with MELAS

INTRODUCTION

The exact mechanism of the mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) remain unclear. Diffusion-weighted imaging (DWI) is a magnetic resonance (MR) imaging technique for studying the pathophysiologic change of the MELAS. The purpose of the study is to see whether the apparent diffusion coefficient (ADC) of MELAS in the non-affected areas is different from the ADC of the normal subjects and to speculate the pathophysiological mechanisms of the MELAS.

METHODS

Sixteen cases of MELAS were retrospectively analyzed. Thirty healthy subjects were chosen to constitute the control group. All of them were performed on the 3.0T whole-body MR scanner with axial view T2 fluid attenuated inversion recovery (flair), T2-weighted imaging, T1flair, and DWI. An ADC map was reconstructed in the workstation. Two to five regions of interest were put in the non-affected frontal lobe and basal ganglia. All data took statistical analysis.

RESULTS

There were significant differences between the ADC of the patients with MELAS and the controls in the non-affected areas, including the superior frontal gyrus, precentral gyrus, corpus striatum, thalamus, and white matter of the semi-oval centrum.

CONCLUSION

ADCs in the non-affected areas of the patients with MELAS are higher than those of the normal subjects. Pathological changes take place in the non-affected areas of the patients with MELAS.

Detection of lactate with a hadamard slice selected, selective multiple quantum coherence, chemical shift imaging sequence (HDMD-SelMQC-CSI) on a clinical MRI scanner: Application to tumors and muscle ischemia

Lactate is an important metabolite in normal and malignant tissues detectable by NMR spectroscopy; however, it has been difficult to clinically detect the lactate methyl resonance because it is obscured by lipid resonances. The selective homonuclear multiple quantum coherence transfer technique offers a method for distinguishing lipid and lactate resonances. We implemented a three-dimensional selective homonuclear multiple quantum coherence transfer version with Hadamard slice selection and two-dimensional phase encoding (Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging) on a conventional clinical MR scanner. Hadamard slice selection is explained and demonstrated in vivo. This is followed by 1-cm(3) resolution lactate imaging with detection to 5-mM concentration in 20 min on a 3-T clinical scanner. An analysis of QSel gradient duration and amplitude effects on lactate and lipid signal is presented. To demonstrate clinical feasibility, a 5-min lactate scan of a patient with a non-Hodgkin's lymphoma in the superficial thigh is reported. The elevated lactate signal coincides with the T(2)-weighted image of this tumor. As a test of selective homonuclear multiple quantum coherence transfer sensitivity, a thigh tourniquet was applied to a normal volunteer and an increase in lactate was detected immediately after tourniquet flow constriction. In conclusion, the Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging sequence is demonstrated on a phantom and in two lipid-rich, clinically relevant, in vivo conditions.

Cerebral oxygen and glucose metabolism in patients with mitochondrial m.3243A>G mutation

The m.3243A>G mutation is the most common pathogenic mutation in mitochondrial DNA. It leads to defective oxidative phosphorylation, decreased oxygen consumption and increased glucose utilization and lactate production in vitro. However, oxygen and glucose metabolism has not been studied in the brain of patients harbouring the m.3243A>G mutation. Therefore, 14 patients with the m.3243A>G mutation, not experiencing acute stroke-like episodes and 14 age-matched controls underwent positron emission tomography using 2-[(18)F]fluoro-2-deoxyglucose, [(15)O]H(2)O and [(15)O]O(2) as the tracers during normoglycaemia. The metabolic rate of oxygen and glucose were determined using a quantitative region of interest analysis. Metabolites in unaffected periventricular tissue were measured using magnetic resonance spectroscopy. We found that the cerebral metabolic rate of oxygen was decreased by 26% (range 18%-29%) in the grey as well as the white matter of patients with the m.3243A>G mutation. A decrease in the metabolic rate of glucose was found with predilection to the posterior part of the brain. No major changes were detected in cerebral blood flow or the number of white matter lesions. Our results show that the m.3243A>G mutation leads to a global decrease in oxygen consumption in the grey matter including areas where no other signs of disease were present.

Pathophysiologic evaluation of MELAS strokes by serially quantified MRS and CASL perfusion images

PURPOSE

To clarify the roles of serial MR spectroscopy (MRS) and continuous arterial spin labeling (CASL) perfusion images for evaluating cerebral lesions in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS).

MATERIALS AND METHODS

Two cases of MELAS followed up serially using MRS and CASL images in addition to routine MR imaging were enrolled.

RESULTS

Newly appeared lesions assessed by MRS revealed increased lactate doublets which correlated well with CSF lactate level, and these showed a decreasing trend after treatment, although conventional T2 weighted images revealed hyper-intensity in both phases. Spectra from normally appearing white matter depicted slight lactate peaks during clinical exacerbation periods with marked elevation of CSF lactate and showed a decreasing NAA concentration during the prolonged course. In CASL images, acute lesions of the disease were clearly visible as hyper-perfusion foci, and chronic lesions were demonstrated as hypo- or iso-perfusion regions.

CONCLUSION

The detection of lactate peaks in the MR spectrum from normally appearing white matter may be considered as systemic lactic acidosis or an exacerbation of MELAS, and active lesions can be distinguished from chronic inactive lesions by the increase of lactate peaks in MRS or the state of hyper-perfusion in CASL images.

Ventricular cerebrospinal fluid lactate is increased in chronic fatigue syndrome compared with generalized anxiety disorder: an in vivo 3.0 T (1)H MRS imaging study

Chronic fatigue syndrome (CFS) is a controversial diagnosis because of the lack of biomarkers for the illness and its symptom overlap with neuropsychiatric, infectious, and rheumatological disorders. We compared lateral ventricular volumes derived from tissue-segmented T(1)-weighted volumetric MRI data and cerebrospinal fluid (CSF) lactate concentrations measured by proton MRS imaging ((1)H MRSI) in 16 subjects with CFS (modified US Centers for Disease Control and Prevention criteria) with those in 14 patients with generalized anxiety disorder (GAD) and in 15 healthy volunteers, matched group-wise for age, sex, body mass index, handedness, and IQ. Mean lateral ventricular lactate concentrations measured by (1)H MRSI in CFS were increased by 297% compared with those in GAD (P < 0.001) and by 348% compared with those in healthy volunteers (P < 0.001), even after controlling for ventricular volume, which did not differ significantly between the groups. Regression analysis revealed that diagnosis accounted for 43% of the variance in ventricular lactate. CFS is associated with significantly raised concentrations of ventricular lactate, potentially consistent with recent evidence of decreased cortical blood flow, secondary mitochondrial dysfunction, and/or oxidative stress abnormalities in the disorder.

MR spectroscopy of the brain in Leigh syndrome

Brain magnetic resonance spectroscopy in two patients with Leigh syndrome revealed the presence of lactate in gray and white matter brain tissue and relatively high choline levels in the white matter. The latter observation, most probably related to an ongoing demyelination process, underlines specific involvement of white matter metabolism in Leigh syndrome even in cases without involvement of the white matter as visualized on MRI. Magnetic resonance spectroscopy might thus be of help in differentiating Leigh syndrome from a range of other mitochondrial diseases, such as ophthalmoplegia and Kearns-Sayre syndrome, showing lack of lactate in brain tissues appearing normal on MRI.

Serial brain imaging analysis of stroke-like episodes in MELAS

We report 2 patients of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) and consider the pathophysiology of stroke-like lesions, using magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI) on MRI, perfusion imaging on MRI, and 1H magnetic resonance spectroscopy (1H-MRS). In Patient 1, T2-weighted imaging (T2-WI) on MRI at onset and even at 44 days after onset of the stroke-like episode showed high intensity in left parietal, temporal, and occipital lobe lesions. In the temporal lobe lesion, the apparent diffusion coefficient (ADC) at 44 days after onset was higher (average: 1.219x10(-3)mm2/s) than that in a normal region (average: 0.796x10(-3)mm2/s). (1)H-MRS of the left parietal lobe lesion at the same day showed a decrease in N-acetylaspartate/(creatine+phosphocreatine) (NAA/Cr) (0.43) and a peak in lactate. 1H-MRS of the contralateral side at the same day showed NAA/Cr (1.57) and no peak in lactate. Thereafter, ADC gradually decreased and NAA/Cr gradually increased, and the peak in lactate disappeared in the lesion. In Patient 2, T2-WI at onset showed high intensity in bilateral occipital lobe lesions. In the left occipital lobe lesion, ADC at the same day was higher (1.082x10(-3)mm2/s) than that in a normal region (average: 0.841x10(-3)mm2/s). (1)H-MRS of the left occipital lobe lesion at the same day showed a decrease of NAA (3.0mM) and a peak in lactate (13.1mM) (measured by LCModel). In 1H-MRS of the normal left parietooccipital lobe at 4 months before onset, NAA was 7.6mM and there was no peak in lactate (0mM). Perfusion imaging at onset showed high intensity in bilateral occipital lobes, which indicated hyperperfusion in stroke-like lesions. Thereafter, ADC gradually decreased and the peak in lactate partially decreased, and the low concentration of NAA persisted (regardless of the partial recovery) in the lesion. These results suggest that the stroke-like episodes is related to vasogenic edema, hyperperfusion, and neuronal damage. Acute oxidative phosphorylation defect may have a crucial role in the pathophysiology of stroke-like episodes.

NP031112, a thiadiazolidinone compound, prevents inflammation and neurodegeneration under excitotoxic conditions: potential therapeutic role in brain disorders

Inflammation and neurodegeneration coexist in many acute damage and chronic CNS disorders (e.g., stroke, Alzheimer's disease, Parkinson's disease). A well characterized animal model of brain damage involves administration of kainic acid, which causes limbic seizure activity and subsequent neuronal death, especially in the CA1 and CA3 pyramidal cells and interneurons in the hilus of the hippocampus. Our previous work demonstrated a potent anti-inflammatory and neuroprotective effect of two thiadiazolidinones compounds, NP00111 (2,4-dibenzyl-[1,2,4]thiadiazolidine-3,5-dione) and NP01138 (2-ethyl-4-phenyl-[1,2,4]thiadiazolidine-3,5-dione), in primary cultures of cortical neurons, astrocytes, and microglia. Here, we show that injection of NP031112, a more potent thiadiazolidinone derivative, into the rat hippocampus dramatically reduces kainic acid-induced inflammation, as measured by edema formation using T2-weighted magnetic resonance imaging and glial activation and has a neuroprotective effect in the damaged areas of the hippocampus. Last, NP031112-induced neuroprotection, both in vitro and in vivo, was substantially attenuated by cotreatment with GW9662 (2-chloro-5-nitrobenzanilide), a known antagonist of the nuclear receptor peroxisome proliferator-activated receptor gamma, suggesting that the effects of NP031112 can be mediated through activation of this receptor. As such, these findings identify NP031112 as a potential therapeutic agent for the treatment of neurodegenerative disorders.

Brain Magnetic Resonance in the Diagnostic Evaluation of Mitochondrial Encephalopathies

Brain MR imaging techniques are important ancillary tests in the diagnosis of a suspected mitochondrial encephalopathy since they provide details on brain structural and metabolic abnormalities. This is particularly true in children where non-specific neurologic symptoms are common, biochemical findings can be marginal and genetic defects may be not discovered. MR imaging modalities include conventional, or structural, imaging (MRI) and functional, or ultrastructural, imaging (spectroscopy, MRS; diffusion, DWI-ADC; perfusion, DSCI—ASL). Among them MRI and MRS are the main tools for diagnosis and work up of MD, and this review will focus mainly on them. The MRI findings of MD are very heterogeneous, as they depend on the metabolic brain defects, age of the patient, stage and severity of the disease. No correlation has been found between genetic defects and neuroimaging picture; however, some relationships between MR findings and clinical phenotypes may be identified. Different combinations of MRI signal abnormalities are often encountered but the most common findings may be summarized into three main MR patterns: (i) non-specific; (ii) specific; (iii) leukodystrophic-like. Regarding the functional MR techniques, only proton MRS plays an important role in demonstrating an oxidative metabolism impairment in the brain since it can show the accumulation of lactate, present as a doublet peak at 1.33 ppm. Assessment of lactate should be always performed on brain tissue and on the ventricular cerebral spinal fluid. As for MRI, metabolic MRS abnormalities can be of different types, and two distinct patterns can be recognized: non-specific and specific. The specific metabolic profiles, although not frequent to find, are highly pathognomonic of MD. The un-specific metabolic profiles add value to structural images in allowing to define the lesion load and to monitor the response to therapy trials.

Evolution of brain imaging abnormalities in mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes

An 18-year-old man developed consecutive homonymous hemianopias that were eventually attributed to mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). The diagnosis was initially suspected when brain CT scans showed bilateral dystrophic basal ganglia calcifications and MR spectroscopy later showed a prominent lactate peak. Diffusion-weighted MRI showed progressive evolution of restricted proton diffusion at the margins of the lesion from day 3 through 3 weeks. Genetic testing from peripheral blood confirmed an A3243G transition in the patient's MTTL1 gene encoding the transfer RNA for leucine. The patient's visual function improved, but severe atrophy of gray and white matter was visible on MRI.

Central nervous system manifestations of mitochondrial disorders

The central nervous system (CNS) is, after the peripheral nervous system, the second most frequently affected organ in mitochondrial disorders (MCDs). CNS involvement in MCDs is clinically heterogeneous, manifesting as epilepsy, stroke-like episodes, migraine, ataxia, spasticity, extrapyramidal abnormalities, bulbar dysfunction, psychiatric abnormalities, neuropsychological deficits, or hypophysial abnormalities. CNS involvement is found in syndromic and non-syndromic MCDs. Syndromic MCDs with CNS involvement include mitochondrial encephalomyopathy, lactacidosis, stroke-like episodes syndrome, myoclonic epilepsy and ragged red fibers syndrome, mitochondrial neuro-gastrointestinal encephalomyopathy syndrome, neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome, mitochondrial depletion syndrome, Kearns-Sayre syndrome, and Leigh syndrome, Leber's hereditary optic neuropathy, Friedreich's ataxia, and multiple systemic lipomatosis. As CNS involvement is often subclinical, the CNS including the spinal cord should be investigated even in the absence of overt clinical CNS manifestations. CNS investigations comprise the history, clinical neurological examination, neuropsychological tests, electroencephalogram, cerebral computed tomography scan, and magnetic resonance imaging. A spinal tap is indicated if there is episodic or permanent impaired consciousness or in case of cognitive decline. More sophisticated methods are required if the CNS is solely affected. Treatment of CNS manifestations in MCDs is symptomatic and focused on epilepsy, headache, lactacidosis, impaired consciousness, confusion, spasticity, extrapyramidal abnormalities, or depression. Valproate, carbamazepine, corticosteroids, acetyl salicylic acid, local and volatile anesthetics should be applied with caution. Avoiding certain drugs is often more beneficial than application of established, apparently indicated drugs.

Pitfalls in the diagnosis of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes

We describe a patient with genetically- and biochemically-proven mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) who was initially misdiagnosed as having had multiple ischemic strokes in part because the clinical presentation appeared to be acute, the MRI of lesions showed restricted diffusion, and the brain biopsy showed features suggestive of stroke. This report emphasizes the pitfalls in the diagnosis of MELAS and points out the similarities and differences between MELAS and ischemic stroke.