MELAS: Clinical and pathologic correlations with MRI, xenon/CT, and MR spectroscopy

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.

Mitochondrial Migraine: Disentangling the angiopathy paradigm in m.3243A>G patients

Migraine, characterized by recurrent attacks of predominantly unilateral throbbing headache, affects approximately 15% of the adult population and is an important cause of disability worldwide. Knowledge required for the development of new classes of antimigraine drugs might come from studying rare metabolic diseases associated with migraine. An illustrative example of a monogenetic disorder associated with migraine is the spectrum of disorders caused by the m.3243A>G mutation in the mitochondrial transfer RNA Leucine. Reported migraine prevalence figures in patients with this particular mutation vary considerably, but compared to the general population, m.3243A>G patients have a higher migraine prevalence. This burdensome symptom might sometimes even be the only clinical feature in maternal relatives carrying the m.3243A>G mutation. Although the exact sequence of events and the relative importance of factors underlying migraine in m.3243A>G MELAS spectrum disorders are still enigmatic, substantial evidence in man exist that dysfunctional mitochondria in both the vascular, the smooth muscle cells and the neuronal system and the interaction between these are at the starting point of the migraine developing pathophysiological cascade. Exclusively based on results of studies performed in patients harboring the m.3243A>G mutation, either in vivo or ex vivo, we here summarize our current understanding of mitochondrial angiopathy associated migraine in m.3243A>G patients which knowledge might lead to potential new avenues for migraine drug development.

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.

Distinctive distribution of brain volume reductions in MELAS and mitochondrial DNA A3243G mutation carriers: A voxel-based morphometric study

OBJECTIVE

The aim of this study was to investigate the clinically latent brain atrophy of patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) harboring a mitochondrial DNA A3243G mutation (A3243G) and A3243G carriers without stroke-like episodes (SEs).

METHODS

We used voxel-based morphometry (VBM) with magnetic resonance imaging to investigate gray matter (GM) and white matter (WM) volume reductions in four MELAS patients and in five A3243G carriers compared to 16 healthy controls. In addition, we investigated the regions of previous SEs using conventional MRI.

RESULTS

All four MELAS patients showed significant GM volume reductions in the left superior parietal lobule (SPL), right precuneus, right middle temporal gyrus (MTG), and bilateral posterior lobes of the cerebellum. These areas of GM volume reduction were beyond the regions of previous SEs. As for A3243G carriers, GM volume reductions in the left SPL, right precuneus, right MTG, and bilateral posterior lobes of the cerebellum were detected in three, one, two, and five subjects, respectively. All four MELAS patients showed significant WM volume reductions in the bilateral or unilateral temporal sub-gyral regions, which were included in the regions of previous SEs. No A3243G carriers showed WM volume reductions.

CONCLUSION

The distribution patterns of GM volume reductions in VBM may reflect a common vulnerability of the brains among MELAS patients and A3243G carriers.

A case of acute onset succinic semialdehyde dehydrogenase deficiency: neuroimaging findings and literature review

BACKGROUND

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder of γ-aminobutyric acid metabolism, leading to elevated levels of γ-aminobutyric acid and γ-hydroxybutyric acid in cerebrospinal fluid.

PATIENT

We describe the neuroimaging findings of a previously healthy 6-month-old girl with acute onset of lethargy, hypotonia, and choreiform movements, and a subsequent diagnosis of SSADH deficiency. Magnetic resonance (MR) imaging of the brain revealed symmetric T2 hyperintense signal abnormalities and reduced diffusivity of the globus pallidi bilaterally. Arterial spin-labeling perfusion MR imaging suggested bilateral hyperperfusion of the globus pallidi. MR spectroscopy of the thalamus and frontal lobe white matter revealed increased signal intensity in the glutamate and glutamine region of the spectra between 2.1 and 2.4 ppm.

CONCLUSION

The unique early imaging findings described here may be attributable to bioenergetic failure and deficiency in mitochondrial energy metabolism and are consistent with SSADH-knockout mice studies.

Diagnostic value of MRS-quantified brain tissue lactate level in identifying children with mitochondrial disorders

Objectives

Magnetic resonance spectroscopy (MRS) of children with or without neurometabolic disease is used for the first time for quantitative assessment of brain tissue lactate signals, to elaborate on previous suggestions of MRS-detected lactate as a marker of mitochondrial disease.

Methods

Multivoxel MRS of a transverse plane of brain tissue cranial to the ventricles was performed in 88 children suspected of having neurometabolic disease, divided into ‘definite’ (n = 17, ≥1 major criteria), ‘probable’ (n = 10, ≥2 minor criteria), ‘possible’ (n = 17, 1 minor criterion) and ‘unlikely’ mitochondrial disease (n = 44, none of the criteria). Lactate levels, expressed in standardized arbitrary units or relative to creatine, were derived from summed signals from all voxels. Ten ‘unlikely’ children with a normal neurological exam served as the MRS reference subgroup. For 61 of 88 children, CSF lactate values were obtained.

Results

MRS lactate level (>12 arbitrary units) and the lactate-to-creatine ratio (L/Cr >0.22) differed significantly between the definite and the unlikely group (p = 0.015 and p = 0.001, respectively). MRS L/Cr also differentiated between the probable and the MRS reference subgroup (p = 0.03). No significant group differences were found for CSF lactate.

Conclusion

MRS-quantified brain tissue lactate levels can serve as diagnostic marker for identifying mitochondrial disease in children.

Key points

• MRS-detected brain tissue lactate levels can be quantified.

• MRS lactate and lactate/Cr are increased in children with mitochondrial disease.

• CSF lactate is less suitable as marker of mitochondrial disease.

Neuroimaging in mitochondrial disorders

Mutations in either nuclear DNA or mitochondrial DNA can result in disruption of oxidative phosphorylation and lead to mitochondrial dysfunction. Mitochondrial disease manifestations occur predominantly in the central nervous system, peripheral nervous system, and/or involve several organ systems. The consequences range from manifestations of a single organ or tissues, such as muscle fatigue, if confined only to muscle, seizures, intellectual disabilities, dementia, and stroke (if to the central nervous system), leading to disability or even early death. The definitive diagnosis of a mitochondrial disorder can be difficult to establish. Criteria and checklists have been established and are more reflective of adult disease. However, in children, when symptoms suggest a mitochondrial disease, neuroimaging features may have more diagnostic impact and additionally these can be used to follow the course, evolution, and recovery of the disease. This review will demonstrate the common neuroimaging patterns in patients with mitochondrial disorders and point out how various newer neuroimaging modalities may be exploited to glean information as to the different aspects of mitochondrial dysfunction or resulting neurological and cognitive disruption, although reports in the literature using these methods remain sparse.

[A case of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) with treatment-resistant status epilepticus that was effectively treated with lamotrigine]

A 16-year-old woman with MELAS developed fever and myoclonic epilepsy which improved with conventional anti-epileptic drugs. Since seizures recurred one month after successful treatment, the doses of phenobarbital, clonazepan, and valproate were increased. However, there was no improvement and status epilepticus continued. The addition of lamotrigine resulted in a decreased frequency and good control of seizures. This case is important, showing satisfactory results from the addition of lamotrigine for treatment-resistant status epilepticus.

Steroid responsive A3243G mutation MELAS: clinical and radiographic evidence for regional hyperperfusion leading to neuronal loss

INTRODUCTION

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a multisystem disorder caused by systemic cellular metabolic derangement that is characterized predominantly by rapidly progressive deterioration of the central nervous system.

CASE REPORT

We describe a patient with an abrupt onset of rapidly recurring episodes of aphasia, hemianopsia, and parietal pseudocerebellar ataxia, leading to the diagnosis of A3243G mutation MELAS. These stroke-like episodes appeared to be initiated by metabolic derangement, as evidenced by lactic-acid elevation in the cerebral spinal fluid and lactate peaks observed on magnetic resonance spectroscopy. Magnetic resonance imaging further revealed that neuronal loss during the acute episodes occurred in regions of paradoxically increased cerebral blood flow. Diffusion-tensor and arterial-spin-labeled perfusion imaging showed that the volume of tissue loss after the stroke-like episodes greatly exceeded the limits of the cortical areas affected by the initial metabolic insult. The patient was consented to a trial of compassionate use, high-dose intravenous corticosteroids, resulting in marked and sustained clinical improvement.

CONCLUSIONS

The majority of neurons lost in an acute episode are injured not by a primary failure to meet metabolic demand, but by a poorly regulated compensatory hyperperfusion response. Regional hyperperfusion leads to apoptotic cell death through a progression from vasogenic to cytotoxic edema. The efficacy of corticosteroids in our study patient demonstrates that inflammatory mediators and blood-brain barrier dysfunction may play a role in the pathophysiological cascade that leads to the regional hyperperfusion in MELAS.

Voxelwise analysis of diffusion tensor imaging and structural MR imaging in patients with the m.3243A>G mutation in mitochondrial DNA

BACKGROUND AND PURPOSE

The m.3243A>G mutation is the most common pathogenic mutation in mtDNA; tissues with high dependence on aerobic energy metabolism, such as the brain, heart, and skeletal muscle, are most affected by the ensuing mitochondrial dysfunction. We hypothesized that the m.3243A>G mutation manifests as disturbances in white matter microstructural integrity and volumetric changes in the brain.

MATERIALS AND METHODS

DTI and structural MR imaging were performed on 15 adult patients with the m.3243A>G mutation and 14 healthy age-matched controls. Voxelwise analysis of the DTI data was performed to reveal possible differences in FA and MD values. Additionally, normalized brain tissue volumes of the subjects were measured, and voxelwise analysis of gray matter was performed to assess volumetric changes in the brain.

RESULTS

Among patients with m.3243A>G mutation, voxelwise analysis of the DTI data revealed significantly reduced FA in several areas located mainly in the occipital lobes, thalami, external and internal capsules, brain stem, cerebellar peduncles, and cerebellar white matter. There were no differences in MD values between the patients and the controls. Analysis of the structural MR imaging data revealed reduced total volume of gray and white matter in patients with m.3243A>G mutation, and VBM analysis identified areas of significant gray matter loss mainly in the occipital lobes and cerebellum.

CONCLUSIONS

Our findings show that patients with m.3243A>G mutation have mild microstructural damage leading to loss of directional organization of white matter and reduced brain volumes.

Diffusion and perfusion characteristics of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) in thirteen patients

Objective

We analyzed the diffusion and perfusion characteristics of acute MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) lesions in a large series to investigate the controversial changes of the apparent diffusion coefficient (ADC) that were reported in prior studies.

Materials and Methods

We analyzed 44 newly appearing lesions during 28 stroke-like episodes in 13 patients with MELAS. We performed a visual assessment of the MR images including the ADC and perfusion maps, comparison of the ADC between the normal and abnormal areas, comparison of % ADC between the 44 MELAS lesions and the 30 acute ischemic infarcts. In addition, the patterns of evolution on follow-up MR images were analyzed.

Results

Decreased, increased, and normal ADCs were noted in 16 (36%), 16 (36%), and 12 (27%) lesions, respectively. The mean % ADC was 102 ± 40.9% in the MELAS and 64 ± 17.8% in the acute vascular infarcts (p < 0.001), while perfusion imaging demonstrated hyper-perfusion in six acute MELAS lesions. On follow-up images, resolution, progression, and tissue loss were noted in 10, 4, and 17 lesions, respectively.

Conclusion

The cytotoxic edema gradually evolves following an acute stroke-like episode in patients with MELAS, and this may overlap with hyper-perfusion and vasogenic edema. The edematous swelling may be reversible or it may evolve to encephalomalacia, suggesting irreversible damage.

Vascular involvement in the pathogenesis of mitochondrial encephalomyopathies

OBJECTIVE

The aim of this study was to perform perfusion CT imaging in the acute phase of myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), to assess whether these patients had cerebral perfusion abnormalities. Furthermore, the pathology of muscle vessel was evaluated, to explore the role of vasculopathy and ischemic events in the pathogenesis of mitochondrial encephalomyopathies.

METHODS

Computed tomography perfusion (CTP) imaging was applied to the evaluation of brain perfusion during the symptomatic period of mitochondrial encephalomyopathies. Mitochondria structures in the blood vessels wall within muscle fibers were observed by light and electron microscopy analyses.

RESULTS

Neuroimaging studies demonstrated uni- and bilateral lesions predominantly in the occipital and temporal-parietal lobes. Compared with the healthy control subjects, significant decreases in cerebral blood flow and cerebral blood volume were noted in affected brain areas of individuals with MELAS. In particular, mean transit time and the time to peak were prolonged both in lesion and non-lesion brain areas. Muscle pathology showed large granular deposits on vessel wall as demonstrated by succinic acid dehydrogenase staining. Electron microscopy of blood vessels revealed swelling of cristae and a striking increase in the number of mitochondria in the smooth muscle and endothelial cells.

CONCLUSION

Insufficient cerebral perfusion or vascular reserve and secondary metabolic dysfunction may represent an important feature of the pathogenesis of the stroke-like episodes in MELAS.

Initial experiences with proton MR spectroscopy in treatment monitoring of mitochondrial encephalopathy

PURPOSE

Mitochondrial encephalopathy (ME) is a rare disorder of energy metabolism. The disease course can roughly be evaluated by clinical findings. The purpose of this study was to evaluate metabolic spectral changes using proton MR spectroscopy (MRS), and to establish a way to monitor ME by neuroimaging.

MATERIALS AND METHODS

Proton MRS data were retrospectively reviewed in 12 patients with muscle biopsy-confirmed ME (M : F = 7 : 5, Mean age = 4.8 years). All received 1H-MRS initially and also after a ketogenic diet and mitochondrial disease treatment cocktail (follow up average was 10.2 months). Changes of N-acetylaspartate/ creatine (NAA/Cr) ratio, choline/creatine (Cho/Cr) ratio, and lactate peak in basal ganglia at 1.2 ppm were evaluated before and after treatment. Findings on conventional T2 weighted MR images were also evaluated.

RESULTS

On conventional MRI, increased basal ganglia T2 signal intensity was the most common finding with ME (n = 9, 75%), followed by diffuse cerebral atrophy (n = 8, 67%), T2 hyperintense lesions at pons and midbrain (n = 4, 33%), and brain atrophy (n = 2, 17%). Lactate peak was found in 4 patients; 2 had disappearance of the peak on follow up MRS. Quantitative analysis showed relative decrease of Cho/Cr ratio on follow up MRS (p = 0.0058, paired t-test, two-tailed). There was no significant change in NAA/Cr ratio.

CONCLUSION

MRS is a useful tool for monitoring disease progression or improvement in ME, and decrease or disappearance of lactate peak and reduction of Cho/Cr fraction were correlated well with improvement of clinical symptoms.

Accumulation of oxidative stress around the stroke-like lesions of MELAS patients

To investigate the relationship between oxidative stress and progressive spread of the stroke-like lesions in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) with 3243A>G mutation, we retrospectively analyzed the spread frequency in patients with and without treatment with the radical scavenger edaravone. Oxidative damage and defensive enzymes were histologically evaluated. Spread was significantly less frequent in the patients treated with edaravone. Although 8-hydroxy-2'-deoxyguanosine, a marker for oxidative damage of DNA, was obviously accumulated in peri-lesional surviving neurons, manganese superoxide dismutase and 8-oxoguanine glycosylase 1 were not up-regulated in those neurons. Increased oxidative stress and insufficient defense could be involved in the pathogenesis of the spreading lesions in MELAS.

Genetics of ischaemic stroke

Ischaemic stroke is a heterogeneous multifactorial disorder. Epidemiological data provide substantial evidence for a genetic component to the disease, but the extent of predisposition is unknown. Large progress has been made in single-gene disorders associated with ischaemic stroke. The identification of NOTCH3 mutations in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) has led to new insights on lacunar stroke and small-vessel disease. Studies of sickle-cell disease have drawn attention to the importance of modifier genes and of gene-gene interactions in determining stroke risk. They have further highlighted a potential role of genetics in predicting stroke risk. Little is known about the genes associated with complex multifactorial stroke. There are probably many alleles with small effect sizes. Genetic-association studies on a wide range of candidate pathways, such as the haemostatic and inflammatory system, homocysteine metabolism, and the renin-angiotensin aldosterone system, suggest a weak but significant effect for several at-risk alleles. Genome-wide linkage studies in extended pedigrees from Iceland led to the identification of PDE4D and ALOX5AP. Specific haplotypes in these genes have been shown to confer risk for ischaemic stroke in the Icelandic population, but their role in other populations is unclear. Advances in high-throughput genotyping and biostatistics have enabled new study designs, including genome-wide association studies. Their application to ischaemic stroke requires the collaborative efforts of multiple centres. This approach will contribute to the identification of additional genes, novel pathways, and eventually novel therapeutic approaches to ischaemic stroke.

Neuroimaging of mitochondrial disease

Mitochondrial disease represents a heterogeneous group of genetic disorders that require a variety of diagnostic tests for proper determination. Neuroimaging may play a significant role in diagnosis. The various modalities of nuclear magnetic resonance imaging (MRI) allow for multiple independent detection procedures that can give important anatomical and metabolic clues for diagnosis. The non-invasive nature of neuroimaging also allows for longitudinal studies. To date, no pathonmonic correlation between specific genetic defect and neuroimaging findings have been described. However, certain neuroimaging results can give important clues that a patient may have a mitochondrial disease. Conventional MRI may show deep gray structural abnormalities or stroke-like lesions that do not respect vascular territories. Chemical techniques such as proton magnetic resonance spectroscopy (MRS) may demonstrate high levels of lactate or succinate. When found, these results are suggestive of a mitochondrial disease. MRI and MRS studies may also show non-specific findings such as delayed myelination or non-specific leukodystrophy picture. However, in the context of other biochemical, structural, and clinical findings, even non-specific findings may support further diagnostic testing for potential mitochondrial disease. Once a diagnosis has been established, these non-invasive tools can also aid in following disease progression and evaluate the effects of therapeutic interventions.

Neuropathology of mitochondrial diseases

The term "mitochondrial diseases" (MD) refers to a group of disorders related to respiratory chain dysfunction. Clinical features are usually extremely heterogeneous because MD may involve several tissues with different degrees of severity. Muscle and brain are mostly affected, probably because of their high dependence on oxidative metabolism. Muscle can be the only affected tissue or involved as a part of a multi-system disease; ragged red fibers, accumulation of structurally altered mitochondria and cytochrome-c-oxidase (COX) negative fibers are the main pathological features. In mitochondrial encephalopathies, central nervous system (CNS) structures are affected according to different patterns of distribution and severity. Characteristic lesions are neuronal loss, vasculo-necrotic changes, gliosis, demyelination and spongy degeneration. In accordance with either grey matter or white matter involvement two main groups of diseases may be distinguished. Neuronal loss and vasculo-necrotic multifocal lesions are the common features of grey matter involvement; demyelination and spongy degeneration occur when white matter is affected, often associated with less severe lesions of the grey structures. Grey matter lesions are prevalent in MERRF, MELAS, Alpers and Leigh syndromes. White matter involvement is always seen in Kearns-Sayre syndrome and was recently described in mtDNA depletion syndrome linked to dGK mutations and in the rare conditions associated with complex I and II deficiency. In this review we describe the main histopathological features of muscle and CNS lesions in mitochondrial diseases.

The Neuropsychologic Deficits of MELAS

OBJECTIVE

To examine the neuropsychologic profile of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) and relate it to neuropathologic findings.

BACKGROUND

MELAS is one of over 40 mitochondrial disorders. Symptoms include seizures, strokelike episodes, headaches, memory impairment, hemianopsia, hearing loss, short stature, diffuse limb weakness, exercise intolerance, nausea, and vomiting. Age of onset ranges from 2 to 40 years. A hallmark of MELAS is normal development until the first symptoms appear.

METHOD

Because information regarding the neuropsychologic functioning of these individuals is sparse, we report findings from detailed neuropsychologic evaluations for a 13-year-old white male and a 33-year-old African-American male with MELAS.

RESULTS

Results revealed global patterns of deterioration in executive function, attention, language, memory, visuospatial, and motor functioning. In both patients, brain scans revealed posterior pathology in the absence of frontal pathology.

CONCLUSIONS

We compared our findings with other documented cases and concluded that MELAS is characterized by a pattern of global deterioration. This pattern differs from that observed in other mitochondrial disorders. The absence of identifiable frontal lobe pathology despite the presence of deficits in executive functioning may be related to the distribution patterns of deficient mitochondria and neuronal projection patterns.

Regional cerebral blood flow and cerebrovascular reactivity during chronic stage of stroke-like episodes in MELAS -- implication of neurovascular cellular mechanism

BACKGROUND

Ischemic vascular hypothesis as a causative role in the pathogenesis of stroke-like episodes in MELAS remains to be debated.

METHODS

This study consisted of two parts. Part 1 is a clinicoradiological study during acute stage of 18 consecutive stroke-like episodes in six patients with MELAS. Part 2 is a SPECT study to assess the regional cerebrovascular reactivity (rCVR) to acetazolamide during chronic stage in five patients with MELAS.

RESULTS

Headache and epileptic seizure were the most common presenting symptoms. Unique features of acute stroke-like lesions included progressive spread of cortical lesions with vasogenic edema, focal periodic epileptiform discharges, focal hyperperfusion, and cortical laminar necrosis during subacute stage. During chronic stage, SPECT showed hypoperfusion in non-affected occipital cortex in three patients as well as in previously affected regions in four. The rCVR was preserved in three patients, focally impaired in one, and extensively impaired in one, but relatively preserved in the occipital cortex in all patients.

CONCLUSIONS

Stroke-like episodes could be non-ischemic neurovascular events initiated by neuronal hyperexcitability. Once neuronal hyperexcitability develops in a focal brain region, epileptic activities depolarize adjacent neurons, leading to a propagation of epileptic activities into the surrounding cortex, and resulting in energy imbalance. The mechanisms for neuronal hyperexcitability remain to be elucidated.

Molecular neuropathology of MELAS: level of heteroplasmy in individual neurones and evidence of extensive vascular involvement

Mitochondrial DNA (mtDNA) disease is an important genetic cause of neurological disability. A variety of different clinical features are observed and one of the most common phenotypes is MELAS (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis and Stroke-like episodes). The majority of patients with MELAS have the 3243A>G mtDNA mutation. The neuropathology is dominated by multifocal infarct-like lesions in the posterior cortex, thought to underlie the stroke-like episodes seen in patients. To investigate the relationship between mtDNA mutation load, mitochondrial dysfunction and neuropathological features in MELAS, we studied individual neurones from several brain regions of two individuals with the 3243A>G mutation using dual cytochrome c oxidase (COX) and succinate dehydrogenase (SDH) histochemistry, and Polymerase Chain Reaction Restriction Fragment Lenght Polymorphism (PCR-RFLP) analysis. We found a low number of COX-deficient neurones in all brain regions. There appeared to be no correlation between the threshold level for the 3243A>G mutation to cause COX deficiency within single neurones and the degree of pathology in affected brain regions. The most severe COX deficiency associated with the highest proportion of mutated mtDNA was present in the walls of the leptomeningeal and cortical blood vessels in all brain regions. We conclude that vascular mitochondrial dysfunction is important in the pathogenesis of the stroke-like episodes in MELAS patients. As migraine is a commonly encountered feature in MELAS, we propose that coupling of the vascular mitochondrial dysfunction with cortical spreading depression (CSD) might underlie the selective distribution of ischaemic lesions in the posterior cortex in these patients.

Chronic progressive external ophthalmoplegia: MR spectroscopy and MR diffusion studies in the brain

OBJECTIVE

The purpose of our study was to show how, despite pathognomonic signs of cerebral involvement in chronic progressive external ophthalmoplegia (CPEO), mitochondrial respiratory chain insufficiency is associated with increased lactate and reduced N-acetylaspartate. CPEO and mitochondrial myopathy are caused by mitochondrial DNA mutations leading to impaired oxidative phosphorylation. Cortical and subcortical metabolites, cerebral diffusivity, and structural MRI were assessed to characterize possible subclinical cerebral pathology in CPEO.

SUBJECTS AND METHODS

Ten patients with CPEO (n = 8), mitochondrial myopathy (n = 1), and Kearns-Sayre syndrome (n = 1) and 13 control group volunteers were studied by MRI, both long TE (144) proton MR spectroscopic imaging (1H MRSI), and diffusion-weighted imaging. Relative concentrations of N-acetylaspartate, choline, creatine, and lactate were estimated by Linear Combination of Model Spectra (LCModel) in healthy-appearing white matter, gray matter, and white matter hyperintensities.

RESULTS

Of five patients with cortical atrophy, it was moderate in three and severe in two. One patient had severe and four had moderate cerebellar atrophy. Six of 10 patients showed unspecific white matter lesions, whereas the remainder had hyperintensities in the pyramidal tract (n =2) and middle cerebellar peduncle (n = 1) despite clinical signs. No basal ganglia lesions were found. Physiologic metabolite ratios were normal and lactate was absent in supratentorial healthy-appearing cortex and subcortical white matter. Global diffusion histogram metrics revealed no abnormalities.

CONCLUSION

Normal spectroscopic imaging in radiologic unaffected brain and healthy global brain parenchymal diffusion findings do not support the hypothesis of a generalized cerebral energy loss in CPEO. Bilateral structural alteration of central motor pathways in two patients without clinical pyramidal signs may, however, reflect subclinical axonal injury in predilection sites in some patients.

MR Spectroscopy of Metabolic Disorders

The application of MR spectroscopy (MRS) in pediatric brain disorders yields valued information on pathologic processes, such as ischemia, demyelination, gliosis, and neurodegeneration. Because these processes manifest in inborn errors of metabolism, the purposes of this article are to (1) describe the spectral changes that are associated with the relatively common metabolic disorders, with summaries of known spectroscopic features of these disorders; (2) offer suggestions for recognition and distinction of disorders; and (3) provide general guidelines for MRS implementation. Although many conditions have a similar presentation, MRS offers valuable information for the individual patient in diagnosis and therapy when integrated fully into the clinical setting.

Migraine and white matter hyperintensities

Patients with migraine are at increased risk for white matter hyperintensities detected on magnetic resonance imaging. The presence of nonspecific white matter hyperintensities may cause uncertainty for physicians and anxiety for patients. The pathophysiology and long-term consequences of these lesions are unknown. Occasionally, white matter lesions in a migraineur may indicate an underlying disease such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), or central nervous system vasculitis. The ability to distinguish between nonspecific and disease-specific patterns of white matter hyperintensities in migraine sufferers is important for the practicing clinician.

Magnetic resonance spectroscopy in patients with MELAS

Localized magnetic resonance spectroscopy (MRS) yields sensitive metabolic markers to provide insight into the pathophysiology of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) in vivo. Findings in full MELAS syndrome at 1H MRS of the brain typically include severely elevated lactate and reduced N-acetylaspartate, glutamate, myo-inositol, and total creatine concentrations in stroke-like lesions. Similar but less extreme alterations are also common in gray matter (GM) regions that appear normal at magnetic resonance imaging. Phosphorus spectroscopy of peripheral muscle permits investigation of the bioenergetic status. A decline of the phosphorylation potential indicates a low energy reserve at rest. Phosphocreatine resynthesis during post-exercise recovery is delayed pointing to reduced mitochondrial capacity. As MRS is inherently non-invasive, follow-up studies can be performed to assess treatment response quantitatively.

Serial diffusion-weighted imaging in a patient with MELAS and presumed cytotoxic oedema

A patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) was studied with serial diffusion-weighted MRI (DWI) after stroke-like episodes and the apparent diffusion coefficient (ADC) was measured in an infarct-like lesion. In the acute and subacute stages, the affected area gave high signal on DWI and its ADC was much lower than that in a normal control region. In the chronic stage, the ADC became higher than that in normal brain. We therefore suggest that the stroke-like episodes did not cause vasogenic oedema but were related to energy failure and cytotoxic oedema.

Application of NMR spectroscopy to monitoring MELAS treatment: a case report

1H magnetic resonance spectroscopy (MRS) of the brain and (31)P MRS and saturation transfer of resting skeletal muscle were used to investigate intracellular metabolites and fluxes through the creatine kinase (CK) reaction in a patient with the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). Acute cortical lesions were characterized by severely elevated lactate levels and reduced concentrations of N-acetylaspartyl compounds, glutamate, and myo-inositol. Similar but less extreme alterations were also observed in gray matter regions that appeared normal on magnetic resonance images. Investigation of the gastrocnemius muscle at rest demonstrated a reduced phosphocreatine level, elevated concentrations of inorganic phosphate and free adenosine 5'-diphosphate, and an abnormally low phosphorylation potential. Besides a moderately increased muscular phosphocreatine concentration, none of the metabolic disturbances detected on MRS improved with oral creatine supplementation. Forward and reverse fluxes through the CK reaction did not significantly change upon creatine treatment. Follow-up MRS investigations may thus provide objective markers of treatment response in vivo without the hazards or inconvenience of biopsy.

Ischaemia triggered by spreading neuronal activation is inhibited by vasodilators in rats

It has been previously shown that spreading neuronal activation can generate a cortical spreading ischaemia (CSI) in rats. The purpose of the present study was to investigate whether vasodilators cause CSI to revert to a normal cortical spreading depression (CSD).A KCl-induced CSD travelled from an open cranial window to a closed window where the cortex was superfused with physiological artificial cerebrospinal fluid (ACSF). At the closed window, recordings revealed a short-lasting negative slow potential shift accompanied by a variable, small and short initial hypoperfusion followed by hyperaemia and then oligaemia. In contrast, spreading neuronal activation locally induced CSI at the closed window when ACSF contained a NO. synthase (NOS) inhibitor, N(G)-nitro-L-arginine, and an increased K+ concentration ([K+]ACSF). CSI was characterised by a sharp and prolonged initial cerebral blood flow decrease to 29 +/- 11 % of the baseline and a prolonged negative potential shift. Co-application of a NOá donor, S-nitroso-N-acetylpenicillamine, and NOS inhibitor with high [K+]ACSF re-established a short-lasting negative potential shift and spreading hyperaemia typical of CSD. Similarly, the NO.-independent vasodilator papaverine caused CSI to revert to a pattern characteristic of CSD. In acute rat brain slices, NOS inhibition and high [K+]ACSF did not prolong the negative slow potential shift compared to that induced by high [K+]ACSF alone. The data indicate that the delayed recovery of the slow potential was caused by vasoconstriction during application of high [K+]ACSF and a NOS inhibitor in vivo. This supports the possibility of a vicious circle: spreading neuronal activation induces vasoconstriction, and vasoconstriction prevents repolarisation during CSI. Speculatively, this pathogenetic process could be involved in migraine-induced stroke.

Unusual imaging findings in progressive myoclonus epilepsy

We describe a patient with progressive myoclonus epilepsy (PME), white matter hyperintensities in the corpus callosum, cerebral hemispheres, and left cerebral peduncle on magnetic resonance imaging (MRI), and positive oligoclonal bands. A phosphorus magnetic resonance spectrum was compatible with mitochondrial dysfunction. Abnormal white matter signals are not a feature of the known PME syndromes, although they occur in Leber's hereditary optic neuropathy (LHON). These abnormalities oriented the diagnosis toward mitochondrial disease.

Focal hyperperfusion in a patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes. Case report

A 28-year-old woman presented with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). The diagnosis was based on the results of molecular genetic analysis, which indicated a typical point mutation at the nucleotide pair 3243. Xenon computerized tomography scans obtained during the strokelike episodes revealed the lesion responsible for the symptoms to be an area of focal hyperperfusion, and scans obtained after the episodes revealed an area of hypoperfusion. Pathogenesis of the strokelike episodes appears to be metabolic dysfunction, although the involvement of a vascular event cannot be excluded.

Current status of neuroprotective agents in the treatment of acute ischemic stroke

To keep ischemic brain cells alive, neuroprotective agents target events in the ischemic cascade that might be injurious to the cells. They can be divided broadly into groups that restore ion balance, block receptors, prevent reperfusion injury, or promote neuronal healing. To date, neuroprotective agents have either shown a lack of efficacy in clinical stroke trials or been limited by side effects. Ongoing clinical trials with novel agents are trying to enroll a more homogeneous population of stroke patients in an effort to demonstrate treatment benefit.

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.

Melas syndrome

An 11 year old male presented with headache, vomiting and weakness of right side of body. One day after admission he developed right focal seizures. He had 5 previous episodes of stroke, the first at 11 months age. His milestones were normal upto the first episode but subsequent mile stones were delayed. His serum and CSF lactic acids were raised. Muscle biopsy showed ragged red fibres on modified Gomori-trichrome staining. His EEG, CT scan and MRI were normal this time. The child improved spontaneously after 7 days. His recovery time progressively became shorter with each episode of stroke. Maximum time for recovery was noted during first episode and least in current episode. This is the first report of Melas syndrome in Indian literature.

Effect of coenzyme Q10 in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS): evaluation by noninvasive tissue oximetry

We evaluated the effect of coenzyme Q10 supplementation to two patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) by using noninvasive tissue oximetry with near-infrared spectra of hemoglobin from the quadriceps muscle during bicycle ergometer exercise. Patients showed distinct oxygen consumption patterns reflecting the defect in oxidative phosphorylation and the impairment in oxygen utilization during exercise. Based on the oxygen consumption pattern, we considered one patient as having severe mitochondrial disorder and another patient as having mild one. After coenzyme Q10 supplementation, the oxygen consumption pattern of the patient with the severe form shifted to the mild one, while that of the patient with mild form remained unchanged. The shift of the pattern to the mild form correlated well with reduction of the sum of the serum lactate and pyruvate content during exercise. Noninvasive tissue oximetry may be useful to evaluate the effect of coenzyme Q10 supplementation to patients with mitochondrial encephalomyopathy including MELAS.

Cerebral blood flow and oxygen metabolism before and after a stroke-like episode in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS)

Cerebral blood flow and oxygen metabolism were examined in two patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) using positron emission tomography (PET). Regional cerebral blood flow (rCBF), regional cerebral oxygen metabolic rate (rCMRO2) and regional oxygen extraction fraction (rOEF) were determined with the steady-state technique using oxygen-15-labeled tracers (15O2, C15O2 and C15O). Case 1, a 45-year-old woman, presented with abrupt onset of fluent aphasia. T2-weighted magnetic resonance imaging (MRI) showed a high signal intensity lesion in the left temporoparietal region. The first PET study on day 16 showed increased rCBF and decreased rCMRO2 in the temporal region. In the second PET study, on day 35, rCBF in the temporal region had decreased. Case 2 was a 19-year-old male; the second son of Case 1. He complained of transient blurring of vision, and then generalized tonic-clonic convulsion occurred. A PET study six days before this stroke-like episode demonstrated increased rCBF in both frontal lobes and putamen, where MRI showed lesions after the episode. Focal hyperemia of the lesion antedated and lasted for at least sixteen days after the stroke-like episode in these MELAS patients. These stroke-like episodes appear to be the result of metabolic dysfunction in neural tissue, although the role of an ischemic vascular event cannot be ruled out.

Adult-onset MELAS. Evidence for involvement of neurons as well as cerebral vasculature in strokelike episodes

BACKGROUND

We report a 46-year-old woman with implications regarding pathogenesis of strokelike episodes in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes). She had a 10-month history of episodic seizures, strokes, cognitive decline, vomiting, and ileus. She also had sensorineural hearing loss, insulin-dependent diabetes mellitus of several years' duration, and persistent lactic acidosis. Family history was pertinent for a similar syndrome in her deceased mother (onset in her sixties), for hearing loss and diabetes mellitus in two brothers, and for hearing loss in her only child, a son.

CASE DESCRIPTION

Serial MRIs of the brain revealed severe but evanescent cerebral cortical abnormalities. A left temporal brain biopsy was performed to exclude encephalitis. Light microscopy revealed a diffuse fibrillary gliosis with abundant reactive gemistocytes, focal evidence of ischemic neuronal injury, and edema. Electron microscopy revealed bizarre enlarged mitochondria and changes consistent with cellular edema. Succinate dehydrogenase staining was strongly reactive within cerebral blood vessels and within neurons. A point mutation was subsequently found at nt 3243 of the mitochondrial tRNA(Leu(UUR) gene in peripheral leukocytes and in brain, confirming the clinical diagnosis of MELAS. Quantitation revealed that 82% of brain mitochondria carried the disease mutation, indicating that most, if not all, tissues were affected.

CONCLUSIONS

Our findings suggest that strokelike episodes in MELAS result from defects in neuronal metabolism, as well as in cerebral vasculature.