Proton MR spectroscopic imaging predicts lesion progression on MRI in X-linked adrenoleukodystrophy

Quantitative MRI in leukodystrophies

Leukodystrophies constitute a large and heterogeneous group of genetic diseases primarily affecting the white matter of the central nervous system. Different disorders target different white matter structural components. Leukodystrophies are most often progressive and fatal. In recent years, novel therapies are emerging and for an increasing number of leukodystrophies trials are being developed. Objective and quantitative metrics are needed to serve as outcome measures in trials. Quantitative MRI yields information on microstructural properties, such as myelin or axonal content and condition, and on the chemical composition of white matter, in a noninvasive fashion. By providing information on white matter microstructural involvement, quantitative MRI may contribute to the evaluation and monitoring of leukodystrophies. Many distinct MR techniques are available at different stages of development. While some are already clinically applicable, others are less far developed and have only or mainly been applied in healthy subjects. In this review, we explore the background, current status, potential and challenges of available quantitative MR techniques in the context of leukodystrophies.

MR Neuroimaging in Pediatric Inborn Errors of Metabolism

Inborn errors of metabolism (IEM) are a group of disorders due to functional defects in one or more metabolic pathways that can cause considerable morbidity and death if not diagnosed early. While individually rare, the estimated global prevalence of IEMs comprises a substantial number of neonatal and infantile disorders affecting the central nervous system. Clinical manifestations of IEMs may be nonspecific. Newborn metabolic screens do not capture all IEMs, and likewise, genetic testing may not always detect pathogenic variants. Neuroimaging is a critical component of the work-up, given that imaging sometimes occurs before prenatal screen results are available, which may allow for recognition of imaging patterns that lead to early diagnosis and treatment of IEMs. This review will demonstrate the role of magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (¹H MRS) in the evaluation of IEMs. The focus will be on scenarios where MRI and ¹H MRS are suggestive of or diagnostic for IEMs, or alternatively, refute the diagnosis.

Magnetic resonance spectroscopy as marker for neurodegeneration in X-linked adrenoleukodystrophy

X-linked adrenoleukodsytrophy (ALD) is a genetic neuro-metabolic disorder, causing a slowly progressive myelopathy in adult male and female patients. New disease modifying therapies for myelopathy are under development. This calls for new (imaging) markers able to measure disease severity and progression in clinical trials. In this prospective cohort study, we measured cerebral metabolite levels with Magnetic Resonance Spectroscopy (MRS), and evaluated their potential as biomarkers for disease severity and neurodegeneration in ALD. We used a comprehensive protocol of 3T Magnetic Resonance Spectroscopic Imaging (MRSI) and 7T Single Voxel Spectroscopy (SVS) in a large cohort of adult ALD males without cerebral demyelination. One hundred seven baseline scans - 59 obtained in ALD patients (42 3T MRSI and 17 7T SVS) and 48 obtained in healthy male controls (32 3T MRSI and 16 7T SVS) - and 82 one and two-year follow-up scans (66 3T MRSI and 16 7T SVS) of ALD patients were included. Both protocols showed significantly lower concentration ratios of N-acetylaspartate/creatine (tNAA/tCr) and Glx (glutamine + glutamate)/tCr in the grey and white matter of patients, compared to controls. A novel finding is the higher level of inositol (Ins)/tCr and choline containing compounds (tCho)/tCr in ALD patients without cerebral demyelination. Furthermore, tNAA/tCr correlated strongly with clinical measures of severity of myelopathy. There was no detectable change in metabolite ratios after one-year or two-year follow-up. Our results imply that cerebral metabolite levels - and more specifically the tNAA/tCr ratio - measured with MRS, have potential value as (imaging) biomarkers in ALD.

Imaging in X-Linked Adrenoleukodystrophy

Magnetic resonance imaging (MRI) is the gold standard for the detection of cerebral lesions in X-linked adrenoleukodystrophy (ALD). ALD is one of the most common peroxisomal disorders and is characterized by a defect in degradation of very long chain fatty acids (VLCFA), resulting in accumulation of VLCFA in plasma and tissues. The clinical spectrum of ALD is wide and includes adrenocortical insufficiency, a slowly progressive myelopathy in adulthood, and cerebral demyelination in a subset of male patients. Cerebral demyelination (cerebral ALD) can be treated with hematopoietic cell transplantation (HCT) but only in an early (pre- or early symptomatic) stage and therefore active MRI surveillance is recommended for male patients, both pediatric and adult. Although structural MRI of the brain can detect the presence and extent of cerebral lesions, it does not predict if and when cerebral demyelination will occur. There is a great need for imaging techniques that predict onset of cerebral ALD before lesions appear. Also, imaging markers for severity of myelopathy as surrogate outcome measure in clinical trials would facilitate drug development. New quantitative MRI techniques are promising in that respect. This review focuses on structural and quantitative imaging techniques-including magnetic resonance spectroscopy, diffusion tensor imaging, MR perfusion imaging, magnetization transfer (MT) imaging, neurite orientation dispersion and density imaging (NODDI), and myelin water fraction imaging-used in ALD and their role in clinical practice and research opportunities for the future.

Concurrent axon and myelin destruction differentiates X-linked adrenoleukodystrophy from multiple sclerosis

Cerebral disease manifestation occurs in about two thirds of males with X-linked adrenoleukodystrophy (CALD) and is fatally progressive if left untreated. Early histopathologic studies categorized CALD as an inflammatory demyelinating disease, which led to repeated comparisons to multiple sclerosis (MS). The aim of this study was to revisit the relationship between axonal damage and myelin loss in CALD. We applied novel immunohistochemical tools to investigate axonal damage, myelin loss and myelin repair in autopsy brain tissue of eight CALD and 25 MS patients. We found extensive and severe acute axonal damage in CALD already in prelesional areas defined by microglia loss and relative myelin preservation. In contrast to MS, we did not observe selective phagocytosis of myelin, but a concomitant decay of the entire axon-myelin unit in all CALD lesion stages. Using a novel marker protein for actively remyelinating oligodendrocytes, breast carcinoma-amplified sequence (BCAS) 1, we show that repair pathways are activated in oligodendrocytes in CALD. Regenerating cells, however, were affected by the ongoing disease process. We provide evidence that-in contrast to MS-selective myelin phagocytosis is not characteristic of CALD. On the contrary, our data indicate that acute axonal injury and permanent axonal loss are thus far underestimated features of the disease that must come into focus in our search for biomarkers and novel therapeutic approaches.

ABCD1 dysfunction alters white matter microvascular perfusion

Cerebral X-linked adrenoleukodystrophy is a devastating neurodegenerative disorder caused by mutations in the ABCD1 gene, which lead to a rapidly progressive cerebral inflammatory demyelination in up to 60% of affected males. Selective brain endothelial dysfunction and increased permeability of the blood–brain barrier suggest that white matter microvascular dysfunction contributes to the conversion to cerebral disease. Applying a vascular model to conventional dynamic susceptibility contrast magnetic resonance perfusion imaging, we demonstrate that lack of ABCD1 function causes increased capillary flow heterogeneity in asymptomatic hemizygotes predominantly in the white matter regions and developmental stages with the highest probability for conversion to cerebral disease. In subjects with ongoing inflammatory demyelination we observed a sequence of increased capillary flow heterogeneity followed by blood–brain barrier permeability changes in the perilesional white matter, which predicts lesion progression. These white matter microvascular alterations normalize within 1 year after treatment with haematopoietic stem cell transplantation. For the first time in vivo, our studies unveil a model to assess how ABCD1 alters white matter microvascular function and explores its potential as an earlier biomarker for monitoring disease progression and response to treatment.

Inherited or acquired metabolic disorders

This chapter starts with a description of imaging of inherited metabolic disorders, followed by a discussion on imaging of acquired toxic-metabolic disorders of the adult brain. Neuroimaging is crucial for the diagnosis and management of a number of inherited metabolic disorders. Among these, inherited white-matter disorders commonly affect both the nervous system and endocrine organs. Magnetic resonance imaging (MRI) has enabled new classifications of these disorders that have greatly enhanced both our diagnostic ability and our understanding of these complex disorders. Beyond the classic leukodystrophies, we are increasingly recognizing new hereditary leukoencephalopathies such as the hypomyelinating disorders. Conventional imaging can be unrevealing in some metabolic disorders, but proton magnetic resonance spectroscopy (MRS) may be able to directly visualize the metabolic abnormality in certain disorders. Hence, neuroimaging can enhance our understanding of pathogenesis, even in the absence of a pathologic specimen. This review aims to present pathognomonic brain MRI lesion patterns, the diagnostic capacity of proton MRS, and information from clinical and laboratory testing that can aid diagnosis. We demonstrate that applying an advanced neuroimaging approach enhances current diagnostics and management. Additional information on inherited and metabolic disorders of the brain can be found in Chapter 63 in the second volume of this series.

MR spectroscopy in children: protocols and pitfalls in non-tumorous brain pathology

Proton nuclear magnetic resonance spectroscopy (MRS) delivers information about cell content and metabolism in a noninvasive manner. The diagnostic strength of MRS lies in its evaluation of pathologies in combination with conventional magnetic resonance imaging (MRI). MRS in children has been most widely used to evaluate brain conditions like tumors, infections, metabolic diseases or learning disabilities and especially in neonates with hypoxic-ischemic encephalopathy. This article reviews some basic theoretical considerations, routine procedures, protocols and pitfalls and will illustrate the range of spectrum alterations occurring in some non-tumorous pediatric brain pathologies.

Metabolic, endocrine, and other genetic disorders

Metabolic, endocrine, and genetic diseases of the brain include a very large array of disorders caused by a wide range of underlying abnormalities and involving a variety of brain structures. Often these disorders manifest as recognizable, though sometimes overlapping, patterns on neuroimaging studies that may enable a diagnosis based on imaging or may alternatively provide enough clues to direct further diagnostic evaluation. The diagnostic workup can include various biochemical laboratory or genetic studies. In this chapter, after a brief review of normal white-matter development, we will describe a variety of leukodystrophies resulting from metabolic disorders involving the brain, including mitochondrial and respiratory chain diseases. We will then describe various acidurias, urea cycle disorders, disorders related to copper and iron metabolism, and disorders of ganglioside and mucopolysaccharide metabolism. Lastly, various other hypomyelinating and dysmyelinating leukodystrophies, including vanishing white-matter disease, megalencephalic leukoencephalopathy with subcortical cysts, and oculocerebrorenal syndrome will be presented. In the following section on endocrine disorders, we will examine various disorders of the hypothalamic-pituitary axis, including developmental, inflammatory, and neoplastic diseases. Neonatal hypoglycemia will also be briefly reviewed. In the final section, we will review a few of the common genetic phakomatoses. Throughout the text, both imaging and brief clinical features of the various disorders will be discussed.

Clinical magnetic resonance spectroscopy of the central nervous system

Proton magnetic resonance spectroscopy (1H MRS) is a noninvasive imaging technique that can easily be added to the conventional magnetic resonance (MR) imaging sequences. Using MRS one can directly compare spectra from pathologic or abnormal tissue and normal tissue. Metabolic changes arising from pathology that can be visualized by MRS may not be apparent from anatomy that can be visualized by conventional MR imaging. In addition, metabolic changes may precede anatomic changes. Thus, MRS is used for diagnostics, to observe disease progression, monitor therapeutic treatments, and to understand the pathogenesis of diseases. MRS may have an important impact on patient management. The purpose of this chapter is to provide practical guidance in the clinical application of MRS of the brain. This chapter provides an overview of MRS-detectable metabolites and their significance. In addition some specific current clinical applications of MRS will be discussed, including brain tumors, inborn errors of metabolism, leukodystrophies, ischemia, epilepsy, and neurodegenerative diseases. The chapter concludes with technical considerations and challenges of clinical MRS.

The Role of MR Imaging in the Assessment of Clinical Outcomes in Children with X-Linked Adrenoleukodystrophy after Allogeneic Haematopoietic Stem Cell Transplantation

Background

The aim of the study was to analyse MR images of the brain, including advanced MR techniques, such as single voxel spectroscopy (MRS) and diffusion tensor imaging (DTI), in children with X-linked adrenoleukodystrophy (X-ALD) before and after haematopoietic stem cell transplantation (HSCT) and to establish the imaging criteria which may be helpful in the assessment of disease staging, qualification to HSCT and follow-up.

Material/Methods

Seven boys, aged 5–10 years, (mean 8.14 years) with biochemically proved X-ALD, underwent plain MR imaging with a 1.5 T unit before and after HSCT. Structural images were analyzed using an MRI severity scale (Loes scale). In one patient the follow-up examinations included MRS with the assessment of metabolite ratios (NAA/Cr, Cho/Cr, mI/Cr), as well as DTI with evaluation of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in several white matter tracts.

Results

Two boys had an MRI severity score before HSCT equal to <8 points, and after HSCT they showed no clinical or radiological progression. In 5 patients with a higher severity score (from 8 to 16 points, mean 10.9) before HSCT, clinical and radiological progression was observed (MRI severity score from 17 to 25 points, mean 20.9). Follow-up advanced MRI techniques in one boy showed metabolic alterations, as well as decreased FA and ADC values in all evaluated areas.

Conclusions

Children at an early stage of X-ALD (below 8 points in MRI severity scale) are more likely to benefit from HSCT. DTI and MRS seem to be more useful imaging methods to assess the progression of X-ALD.

Neuroimaging of lipid storage disorders

Lipid storage diseases, also known as the lipidoses, are a group of inherited metabolic disorders in which there is lipid accumulation in various cell types, including the central nervous system, because of the deficiency of a variety of enzymes. Over time, excessive storage can cause permanent cellular and tissue damage. The brain is particularly sensitive to lipid storage as the contents of the central nervous system must occupy uniform volume, and any increases in fluids or deposits will lead to pressure changes and interference with normal neurological function. In addition to primary lipid storage diseases, lysosomal storage diseases include the mucolipidoses (in which excessive amounts of lipids and carbohydrates are stored in the cells and tissues) and the mucopolysaccharidoses (in which abnormal glycosylated proteins cannot be broken down because of enzyme deficiency). Neurological dysfunction can be a manifestation of these conditions due to substrate deposition as well. This review will explore the modalities of neuroimaging that may have particular relevance to the study of the lipid storage disorder and their impact on elucidating aspects of brain function. First, the techniques will be reviewed. Next, the neuropathology of a few selected lipid storage disorders will be reviewed and the use of neuroimaging to define disease characteristics discussed in further detail. Examples of studies using these techniques will be discussed in the text.

Clinical proton MR spectroscopy in central nervous system disorders

A large body of published work shows that proton (hydrogen 1 [(1)H]) magnetic resonance (MR) spectroscopy has evolved from a research tool into a clinical neuroimaging modality. Herein, the authors present a summary of brain disorders in which MR spectroscopy has an impact on patient management, together with a critical consideration of common data acquisition and processing procedures. The article documents the impact of (1)H MR spectroscopy in the clinical evaluation of disorders of the central nervous system. The clinical usefulness of (1)H MR spectroscopy has been established for brain neoplasms, neonatal and pediatric disorders (hypoxia-ischemia, inherited metabolic diseases, and traumatic brain injury), demyelinating disorders, and infectious brain lesions. The growing list of disorders for which (1)H MR spectroscopy may contribute to patient management extends to neurodegenerative diseases, epilepsy, and stroke. To facilitate expanded clinical acceptance and standardization of MR spectroscopy methodology, guidelines are provided for data acquisition and analysis, quality assessment, and interpretation. Finally, the authors offer recommendations to expedite the use of robust MR spectroscopy methodology in the clinical setting, including incorporation of technical advances on clinical units.

Age-related changes in a patient with Pelizaeus-Merzbacher disease determined by repeated 1H-magnetic resonance spectroscopy

A boy with Pelizaeus-Merzbacher disease underwent repeated evaluations by 3-Tesla (1)H-magnetic resonance spectroscopy (MRS). The patient showed overlap of the PLP1. Individuals selected as normal controls for (1)H-magnetic resonance spectroscopy consisted of healthy age-matched children. For (1)H-magnetic resonance spectroscopy, the center of a voxel was positioned in the right parietal lobe. (1)H-magnetic resonance spectroscopy was performed when the patient was 2, 6, 14, and 25 months old. γ-Aminobutyric acid concentration in early childhood was increased compared with that in normal controls. However, the γ-aminobutyric acid concentration in the Pelizaeus-Merzbacher disease patient was normalized at 14 and 25 months. No remarkable changes were observed in choline-containing compounds concentration at any time. These results suggest that the changes in metabolite concentrations during growth can reflect the pathological condition of Pelizaeus-Merzbacher disease. Furthermore, the lack of change in the choline-containing compounds concentration can be useful for differentiating Pelizaeus-Merzbacher disease from other white matter disorders.

Hypoperfusion predicts lesion progression in cerebral X-linked adrenoleukodystrophy

Magnetic resonance imaging sequences such as diffusion and spectroscopy have been well studied in X-linked adrenoleukodystrophy, but no data exist on magnetic resonance perfusion imaging. Since inflammation is known to modulate the microcirculation, we investigated the hypothesis that changes in the local perfusion might be one of the earliest signs of lesion development. Twenty patients with different phenotypes of adrenoleukodystrophy and seven age-matched controls were evaluated between 2006 and 2011. Fluid attenuated inversion recovery, post-contrast T(1)-weighted and normalized dynamic susceptibility contrast magnetic resonance perfusion cerebral blood volume maps were co-registered, segmented when cerebral lesion was present, and normalized cerebral blood volume values were analysed using a Food and Drug Association approved magnetic resonance perfusion software (NordicICE). Clinical and imaging data were reviewed to determine phenotype and status of progression. All eight patients with cerebral adrenoleukodystrophy had an average 80% decrease in normalized cerebral blood volume at the core of the lesion (P < 0.0001). Beyond the leading edge of contrast enhancement cerebral perfusion varied, patients with progressive lesions showed an average 60% decrease in normalized cerebral blood volume (adults P < 0.05; children P < 0.001), while one child with arrested progression normalized cerebral blood volume in this region. In six of seven patients with cerebral adrenoleukodystrophy lesions and follow-up imaging (2-24 month interval period), we found progression of contrast enhancement into the formerly hypoperfused perilesional zone. Asymptomatic, adrenomyeloneuropathy and female heterozygote patients had no significant changes in cerebral perfusion. Our data indicate that decreased brain magnetic resonance perfusion precedes leakage of the blood-brain barrier as demonstrated by contrast enhancement in cerebral adrenoleukodystrophy and is an early sign of lesion progression.

Leukodystrophies

Leukodystrophies comprise a broad group of progressive, inherited disorders affecting mainly myelin. They often present after a variable period of normalcy with a variety of neurologic problems. Though the ultimate diagnosis is not found in many patients with leukodystrophies, distinctive features unique to them aid in diagnosis, treatment and prognostication. The clinical characteristics, etiologies, diagnostic testing and treatment options are reviewed in detail for some of the major leukodystrophies: X-linked adrenoleukodystrophy, Krabbe disease, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease, Alexander disease, Canavan disease, megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease.

Correlating quantitative MR imaging with histopathology in X-linked adrenoleukodystrophy

BACKGROUND AND PURPOSE

Quantitative MR imaging techniques may improve the pathologic specificity of MR imaging regarding white matter abnormalities. Our purposes were to determine whether ADC, FA, MTR, and MRS metabolites correlate with the degree of white matter damage in patients with X-ALD; whether differences in ADC, FA, and MTR observed in vivo are retained in fresh and formalin-fixed postmortem brain tissue; and whether the differences predict histopathology.

MATERIALS AND METHODS

MRS metabolites, MTR, ADC, and FA, were determined in 7 patients with X-ALD in 3 white matter areas (NAWM, active demyelination, and complete demyelination) and were compared with values obtained in 14 controls. MTR, ADC, and FA were assessed in postmortem brains from 15 patients with X-ALD and 5 controls. Values were correlated with the degree of astrogliosis and density of myelin, axons, and cells. Equations to estimate histopathology from MR imaging parameters were calculated by linear regression analysis.

RESULTS

MRS showed increased mIns, Lac, and Cho and decreased tNAA in living patients with X-ALD; the values depended on the degree of demyelination. MTR, ADC, and FA values were different in postmortem than in vivo white matter, but differences related to degrees of white matter damage were retained. ADC was high and FA and MTR were low in abnormal white matter. Correlations between histopathologic findings and MR imaging parameters were strong. A combination of ADC and FA predicted pathologic parameters best.

CONCLUSIONS

Changes in quantitative MR imaging parameters, present in living patients and related to the severity of white matter pathology, are retained in postmortem brain tissue. MR imaging parameters predict white matter histopathologic parameters.

General aspects and neuropathology of X-linked adrenoleukodystrophy

X-adrenoleukodystrophy (X-ALD) is a metabolic, peroxisomal disease affecting the nervous system, adrenal cortex and testis resulting from inactivating mutations in ABCD1 gene which encodes a peroxisomal membrane half-adenosine triphosphate (ATP)-binding cassette transporter, ABCD1 (or ALDP), whose defect is associated with impaired peroxisomal beta-oxidation and accumulation of saturated very long-chain fatty acids (VLCFA) in tissues and body fluids. Several phenotypes are recognized in male patients including cerebral ALD in childhood, adolescence or adulthood, adrenomyeloneuropathy (AMN), Addison's disease and, eventually, gonadal insufficiency. Female carriers might present with mild to severe myeloneuropathy that resembles AMN. There is a lack of phenotype-genotype correlations, as the same ABCD1 gene mutation may be associated with different phenotypes in the same family, suggesting that genetic, epigenetic, environmental and stochastic factors are probably contributory to the development and course of the disease. Degenerative changes, like those seen in pure AMN without cerebral demyelination, are characterized by loss of axons and secondary myelin in the long tracts of the spinal cord, possibly related to the impaired lipid metabolism of VLCFAs and the associated alterations (ie, oxidative damage). Similar lesions are encountered following inactivation of ABCD1 in mice (ABCD1(-)). A different and more aggressive phenotype is secondary to cerebral demyelination, very often accompanied by inflammatory changes in the white matter of the brain and associated with activation of T lymphocytes, CD1 presentation and increased levels of cytokines, gamma-interferon, interleukin (IL)-1alpha, IL-2 and IL-6, Granulocyte macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor-alpha, chemokines and chemokine receptors.

Current and future pharmacological treatment strategies in X-linked adrenoleukodystrophy

Mutations in the ABCD1 gene cause the clinical spectrum of the neurometabolic disorder X-linked adrenoleukodystrophy/adrenomyeloneuropathy (X-ALD/AMN). Currently, the most efficient therapeutic opportunity for patients with the cerebral form of X-ALD is hematopoietic stem cell transplantation and possibly gene therapy of autologous hematopoietic stem cells. Both treatments, however, are only accessible to a subset of X-ALD patients, mainly because of the lack of markers that can predict the onset of cerebral demyelination. Moreover, for female or male X-ALD patients with AMN, currently only unsatisfying therapeutic opportunities are available. Thus, this review focuses on current and urgently needed future pharmacological therapies. The treatment of adrenal and gonadal insufficiency is well established, whereas applications of immunomodulatory and immunosuppressive drugs have failed to prevent progression of cerebral neuroinflammation. The use of Lorenzo's oil and the inefficacy of lovastatin to normalize very-long-chain fatty acids in clinical trials as well as currently experimental and therefore possible future therapeutic strategies are reviewed. The latter include pharmacological gene therapy mediated by targeted upregulation of ABCD2, the closest homolog of ABCD1, antioxidative drug treatment, small molecule histone deacetylase inhibitors such as butyrates and valproic acid, and other neuroprotective attempts.

Early signs of visual perception and evoked potentials in radiologically asymptomatic boys with X-linked adrenoleukodystrophy

The aim was to identify the electrophysiological and psychological signs at a very early stage in asymptomatic boys with childhood cerebral X-linked adrenoleukodystrophy. Flash visual evoked potentials, pattern reversal, and visual event-related potentials were recorded in 6 radiologically asymptomatic boys with adrenoleukodystrophy and 22 control boys. The latency and amplitude of P100 of visual evoked potentials and P1 of event-related potentials were evaluated. Though all patients had normal intelligence quotient, performance intelligence quotient was significantly lower than verbal intelligence quotient in 2 patients. Both P100 and P1 amplitudes were significantly greater in adrenoleukodystrophy than in controls. The difference between performance intelligence quotient and verbal intelligence quotient exhibited significant correlation with P100 amplitude. Enlargement of visual evoked potentials might be a sign of cerebral involvement preceding the appearance of abnormalities on magnetic resonance imaging. Follow-up of asymptomatic boys with both electrophysiological and neuropsychological tests may serve as an aid for deciding the timing of therapeutic intervention.

Cerebral white matter: neuroanatomy, clinical neurology, and neurobehavioral correlates

Lesions of the cerebral white matter (WM) result in focal neurobehavioral syndromes, neuropsychiatric phenomena, and dementia. The cerebral WM contains fiber pathways that convey axons linking cerebral cortical areas with each other and with subcortical structures, facilitating the distributed neural circuits that subserve sensorimotor function, intellect, and emotion. Recent neuroanatomical investigations reveal that these neural circuits are topographically linked by five groupings of fiber tracts emanating from every neocortical area: (1) cortico-cortical association fibers; (2) corticostriatal fibers; (3) commissural fibers; and cortico-subcortical pathways to (4) thalamus and (5) pontocerebellar system, brain stem, and/or spinal cord. Lesions of association fibers prevent communication between cortical areas engaged in different domains of behavior. Lesions of subcortical structures or projection/striatal fibers disrupt the contribution of subcortical nodes to behavior. Disconnection syndromes thus result from lesions of the cerebral cortex, subcortical structures, and WM tracts that link the nodes that make up the distributed circuits. The nature and the severity of the clinical manifestations of WM lesions are determined, in large part, by the location of the pathology: discrete neurological and neuropsychiatric symptoms result from focal WM lesions, whereas cognitive impairment across multiple domains--WM dementia--occurs in the setting of diffuse WM disease. We present a detailed review of the conditions affecting WM that produce these neurobehavioral syndromes, and consider the pathophysiology, clinical effects, and broad significance of the effects of aging and vascular compromise on cerebral WM, in an attempt to help further the understanding, diagnosis, and treatment of these disorders.

Cerebral X-linked adrenoleukodystrophy: follow-up with magnetic resonance imaging

OBJECTIVE

To report a case of childhood cerebral X-linked adrenoleukodystrophy (X-ADL), emphasizing the magnetic resonance imaging (MRI) findings at initial evaluation and at the follow-up.

CASE REPORT

Five year-old boy, who was asymptomatic, presented with diagnosis of X-ADL for MRI evaluation. The initial brain MRI showed a focal area of enhancement at the splenium of the corpus calosum. One year later, the follow-up MRI showed a progression of the corpus calosus lesion, as well as other lesions in the parietal and occipital lobes.

CONCLUSION

The brain MRI follow-up of patients with X-ADL is important to show the progression of the lesions.

Adrénoleucodystrophie liée à l'X☆☆Cet article est publié en partenariat avec Orphanet et disponible sur le site www.orpha.net. © 2007 Orphanet. Publié par Elsevier Masson SAS. Tous droits réservés

X-linked adrenoleukodystrophy (ALD) is a severe neurodegenerative disorder. ALD is characterized by progressive demyelination within the central and peripheral nervous system, adrenal insufficiency (Addison's disease) and accumulation of very-long-chain fatty acids (VLCFA) in plasma, fibroblasts and tissues. The overall incidence of ALD is 1:17,000 including hemizygotes and heterozygotes who are frequently symptomatic. There are two main ALD phenotypes: 1) a cerebral demyelinating form which affects boys between 5-12 years, but also 35% of adult males; 2) a form that mainly involves the spinal cord (adrenomyeloneuropathy, AMN) in adult males between 20-50 years and 50% of heterozygous women after the age of 40 years. AMN presents with progressive spastic paraparesis. Addison's disease may be the first symptom of ALD in boys and adult males. These patients are at risk to develop cerebral ALD or AMN for life. ALD results from mutations in the ABCD1 gene without correlation between genotype and phenotype. The diagnosis of ALD relies upon the measurement of plasma VLCFA levels that allows the identification of 100% affected males and of 80-95% heterozygous women. Because of these false-negative, it is therefore mandatory to search for a mutation in the ABCD1 gene in all women at risk to be heterozygous for ALD. The ABCD1 gene encodes a peroxisomal transmembrane protein (ALD protein) with the structure of an half ATP-binding cassette transporter. It is possible that ALD protein imports VLCFA or VLCFA-CoA into peroxisomes in which they are degraded by a peroxisomal beta-oxidation system. Elongation of VLCFAs is enhanced in fibroblasts from ALD patients and likely contributes to the load of VLCFA in tissues. The underlying mechanisms that lead to cerebral demyelination, axonal degeneration in spinal cord and adrenal insufficiency are unknown. The "toxic" role of VLCFA accumulation remains to be demonstrated. The mechanisms that lead to the inflammatory reaction in cerebral ALD might involve abnormal acylation of gangliosides and phospholipids by VLCFA that would result in immune reaction of brain macrophages and astrocytes bearing CD1 molecules that recognize lipid antigens. De novo mutation of ABCD1 occurs in less than 8% of ALD patients. The genetic counseling aims to identify: 1) women who are at risk to be heterozygous; 2) neurologically asymptomatic boys. It is only at this stage that allogeneic bone marrow transplantation has clinical benefit; 3) ALD patients who have Addison's disease that can lead to sudden death. Prenatal diagnosis (chorionic villus samples, cultured amniotic fluid cells) relies upon DNA based mutation detection techniques, expression of ALD protein and measurement of VLCFA levels. Allogeneic bone marrow transplantation is the only treatment that provides a permanent cure when the procedure is performed at an early stage of cerebral demyelination, i.e when the patients are asymptomatic despite abnormal brain MRI. Treatment of Addison's disease is mandatory but does not modify the course of neurological symptoms. Dietary therapy failed to halt the neurologic progression in cerebral ALD and AMN. It might have a partial preventive effect in boys treated before 6 years of age.

Immune response in leukodystrophies

Although the genetics and biochemistry of leukodystrophies have been extensively explored, the immune response in these disorders has received relatively little attention. Both the disease course and its response to treatment may be highly dependent on the immune system. In this review, we compare three common leukodystrophies, each with a different immune response: (1) X-linked adrenoleukodystrophy, which demonstrates a severe, lymphocytic inflammatory response; (2) metachromatic leukodystrophy, which yields a histiocytic response; and (3) vanishing white-matter disease, in which no inflammation is typically seen. We highlight the biochemical, pathologic, and clinical differences, while focusing on the immune response in each disease. We also review the response of leukodystrophies to immunomodulatory therapies and interventions such as hematopoietic stem-cell transplantation. Future studies may delineate specific inflammatory markers as possible candidates for therapeutic intervention.

Magnetic resonance spectroscopy and metabolic imaging in white matter diseases and pediatric disorders

This review provides the reader with an overview of the magnetic resonance spectroscopy technique and the clinical, pathological, imaging, and metabolic features for select white matter disorders of interest. With this composite summary, the reader should find it easier to implement and interpret spectroscopy in the clinical setting for the diagnosis and monitoring of patients with white matter disorders.

Anomalies cérébrales subtiles de l’Adrénomyéloneuropathie

PURPOSE

To describe subtle brain abnormalities detected on MRI in adult patients with adrenomyeloneuropathy (AMN). Materials and methods. Retrospective evaluation of data acquired prospectively as part of a clinical trial (Riluzole) in 66 adult patients with AMN without obvious brain lesion on MR. All patients underwent brain MR including T1W, T2W, FLAIR and spectroscopy. After a review had been validated by three different reviewers, review of MR images was performed by consensus using a semi-quantitative scale.

RESULTS

Preliminary analysis of MR images confirmed the presence of signal abnormalities involving the corticospinal tracts in 36 patients (54.6%). Additional subtle abnormalities were also detected: white matter palor, mainly parieto-occipital in location, with patchy hyperintensity in 36 patients (54.6%), hyperintense pontocerebellar fibers on T2W and FLAIR in 25 patients (41.7%). The presence of elevated Cho/Cr and mI/Cr ratios, described in the literature, were confirmed.

CONCLUSION

This retrospective study allows the description of an AMN pattern on MRI in patients without white matter or callosal abnormalities.

[Brain magnetic resonance spectroscopy]

MR spectroscopy (MRS) sequences allow noninvasive exploration of brain metabolism during a MRI examination. Their day-to-day use in a clinical setting has recently been improved by simple programming of sequences and automated quantification of metabolites. However, a few simple rules should be observed in the choice of sequences and the location of the voxels so as to obtain an informative, high-quality examination. The research applications of MR spectroscopy, where use of this examination seeks to better understand the pathophysiology of the disease, must be distinguished from its clinical indications, where MRS provides information that can be used directly in patient management. The most significant of the clinical uses are imaging intracranial tumors (positive and differential diagnosis, extension, treatment follow-up), diffuse brain injury, encephalopathies (especially hepatic and HIV-related), and the diagnosis of metabolic disorders.

An approach to MRI of metabolic disorders in children

Inborn errors of metabolism are a difficult group of disorders for the neuroradiologist, as there are few good clinical or neuroradiological criteria for differentiating them. In this review, a technique of diagnosis by pattern recognition, supplemented by metabolic data from proton MR spectroscopy and microstructural data, as assessed by diffusion weighted images, is presented. Proper use of these neuroimaging tools can be very useful for separating these disorders into more manageable groups, and sometimes allows a specific diagnosis to be made.

X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is caused by a defect in the gene ABCD1, which maps to Xq28 and codes for a peroxisomal membrane protein that is a member of the ATP-binding cassette transporter superfamily. X-ALD is panethnic and affects approximately 1:20,000 males. Phenotypes include the rapidly progressive childhood, adolescent, and adult cerebral forms; adrenomyeloneuropathy, which presents as slowly progressive paraparesis in adults; and Addison disease without neurologic manifestations. These phenotypes are frequently misdiagnosed, respectively, as attention-deficit hyperactivity disorder (ADHD), multiple sclerosis, or idiopathic Addison disease. Approximately 50% of female carriers develop a spastic paraparesis secondary to myelopathic changes similar to adrenomyeloneuropathy. Assays of very long chain fatty acids in plasma, cultured chorion villus cells and amniocytes, and mutation analysis permit presymptomatic and prenatal diagnosis, as well as carrier identification. The timely use of these assays is essential for genetic counseling and therapy. Early diagnosis and treatment can prevent overt Addison disease, and significantly reduce the frequency of the severe childhood cerebral phenotype. A promising new method for mass newborn screening has been developed, the implementation of which will have a profound effect on the diagnosis and therapy of X-ALD.

Identification of diffuse and focal brain lesions by clinical magnetic resonance spectroscopy

The purpose of this paper is to facilitate the comparison of magnetic resonance (MR) spectra acquired from unknown brain lesions with published spectra in order to help identify unknown lesions in clinical settings. The paper includes lists of references for published MR spectra of various brain diseases, including pyogenic abscesses, encephalitis (herpes simplex, Rasmussen's and subacute sclerosing panencephalitis), neurocysticercosis, tuberculoma, cysts (arachnoid, epidermoid and hydatid), acute disseminated encephalomyelitis (ADEM), adrenoleukodystrophy (ALD), Alexander disease, Canavan's disease, Krabbe disease (globoid cell leukodystrophy), Leigh's disease, megalencephalic leukoencephalopathy with cysts, metachromatic leukodystrophy (MLD), Pelizaeus-Merzbacher disease, Zellweger syndrome, HIV-associated lesions [cryptococcus, lymphoma, toxoplasmosis and progressive multifocal leukoencephalopathy (PML)], hydrocephalus and tuberous sclerosis. Each list includes information on the echo time(s) (TE) of the published spectra, whether a control spectrum is shown, whether the corresponding image and voxel position are shown and the patient ages if known. The references are listed in the approximate order of usefulness, based on spectral quality, number of spectra, range of echo times and whether the voxel positions are shown. Spectra of Zellweger syndrome, cryptococcal infection, toxoplasmosis and lymphoma are included, along with a spectrum showing propanediol (propylene glycol).

Adrénoleucodystrophie liée à l’X, forme cérébrale de l’adulte

The authors report a case of an X-linked-adrenoleukodystrophy (ALD) in a young adult presenting with hemianopsia. Adult onset cerebral ALD is rare and represents only 3% of cases of ALD. The observation describes clinical data, as well as conventional and spectroscopic MR imaging and related value in prognosis evaluation.

Therapy of X-linked adrenoleukodystrophy

Current therapies for X-linked adrenoleukodystrophy (X-ALD) include replacement therapy with adrenal steroids, which is mandatory for all patients with impaired adrenal function but does not alter neurological progression significantly; dietary therapy with "Lorenzo's Oil," which appears to have a preventive effect in asymptomatic boys whose brain MRI is normal; and hematopoietic stem cell transplantation in patients in the early stage of the cerebral inflammatory phenotype. Application of these interventions requires careful assessment of the patients' phenotype, which often changes over time. Family screening provides important opportunities for disease prevention.

Trends in haematopoietic cell transplantation for inborn errors of metabolism

For the last 25 years, haematopoietic cell transplantation (HCT) has been used as effective therapy for selected inborn errors of metabolism (IEMs), mainly lysosomal storage diseases and peroxisomal disorders. The main rational for HCT in IEMs is based on the provision of correcting enzymes by donor cells within and outside the blood compartment. The ultimate goal of HCT is to achieve a normal or near-normal life and normal neurodevelopment. HCT has been performed for more than 20 diseases. Only for Hurler syndrome, X-ALD and infantile Krabbe disease, are detailed studies available suggesting that HCT is indicated for carefully selected cases. Improvement of transplantation techniques and alternative therapies may change the recommended (contra-)indications for IEM. A recent example of emerging transplantation techniques is the fast availability of unrelated cord blood (UCB). UCB makes HCT feasible in patients with rapidly progressive neurological diseases. Because of the fast availability of UCB and therefore the ability to transplant shortly after diagnosis, there is no indication for patients in a moderate/good clinical condition to receive enzyme replacement therapy (ERT; in Hurler syndrome) prior to or during HCT and can ERT only be considered in patients with poor clinical condition. Mesenchymal stem cell infusions with HCT is an emerging technique, and might be interesting in halting the remaining defects after successful HCT. Improvement in HCT techniques and novel stem cell sources will significantly impact the safety and efficacy of this therapy as well as expand the list of candidate disorders. A good functioning worldwide registry would be necessary to measure the effects of the procedures performed in more detail.

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.

X-linked adrenoleukodystrophy: therapeutic approaches to distinct phenotypes

X-linked adrenoleukodystrophy (X-ALD) in males can present with eight distinct phenotypes, which vary greatly in respect to phenotypic expression, age of onset and rate of progression and therapy. The plasma very long chain fatty acid assay permits precise diagnosis and is already abnormal at birth. The clinical features, molecular biology, pathogenesis, and therapeutic approaches, including the indications for Hematopoietic Stem Cell Transplants (HCT) and dietary therapy are discussed, with emphasis on the asymptomatic, childhood cerebral, and adrenomyeloneuropathy phenotypes. The rationale for neonatal screening and the profound effect that such screening would have on the therapy of X-ALD, including the role of HCT, are discussed.

Efficacy of proton magnetic resonance spectroscopy in neurological diagnosis and neurotherapeutic decision making

Anatomic and functional neuroimaging with magnetic resonance imaging (MRI) includes the technology more widely known as magnetic resonance spectroscopy (MRS). Now a routine automated "add-on" to all clinical magnetic resonance scanners, MRS, which assays regional neurochemical health and disease, is therefore the most accessible diagnostic tool for clinical management of neurometabolic disorders. Furthermore, the noninvasive nature of this technique makes it an ideal tool for therapeutic monitoring of disease and neurotherapeutic decision making. Among the more than 100 brain disorders that fall within this broad category, MRS contributes decisively to clinical decision making in a smaller but growing number. In this review, we will cover how MRS provides therapeutic impact in brain tumors, metabolic disorders such as adrenoleukodystrophy and Canavan's disease, Alzheimer's disease, hypoxia, secondary to trauma or ischemia, human immunodeficiency virus dementia and lesions, as well as systemic disease such as hepatic and renal failure. Together, these eight indications for MRS apply to a majority of all cases seen. This review, which examines the role of MRS in enhancing routine neurological practice and treatment concludes: 1) there is added value from MRS where MRI is positive; 2) there is unique decision-making information in MRS when MRI is negative; and 3) MRS usefully informs decision making in neurotherapeutics. Additional efficacy studies could extend the range of this capability.

Neuroimaging in cerebral palsy

Parents and clinicians concerned about high-risk infants and children with motor delay or cerebral palsy seek information on cause, treatment, prognosis, and recurrence risk. Used in combination with history and examination, neuroimaging studies can improve diagnosis and management. In premature infants, cranial ultrasound is a reliable, noninvasive diagnostic modality. Nuclear magnetic resonance techniques including magnetic resonance imaging and diffusion weighted imaging can be used effectively in neonatal encephalopathies. In children with motor delay and cerebral palsy syndromes including spastic diplegia, quadriplegia, hemiplegia, and extrapyramidal movement disorders, conventional magnetic resonance imaging has become an important determinant of diagnosis and management. The aim of this article is to help clinicians select and interpret imaging studies of benefit in clinical care.

Neuroimaging in leukodystrophies

The application of techniques based on in vivo magnetic resonance to the study of leukodystrophies is evaluated. Magnetic resonance imaging (MRI), the most important neuroimaging modality for patients with leukodystrophies, has proven invaluable for the detection of the extent and etiology of white-matter involvement, diagnosis, and monitoring of disease progression. Proton magnetic resonance spectroscopy, which can detect several brain metabolites, including those related to axonal function and myelination, can provide additional diagnostic and prognostic information and, in some cases, allows a rare insight into the biochemical pathology of leukodystrophies. The potential of other advanced magnetic resonance techniques, including diffusion tensor imaging, magnetization transfer contrast, and molecular imaging, is also discussed. In the future, anatomic and physiologic magnetic resonance techniques are expected to be integrated into a single examination that will provide a detailed characterization of white-matter diseases in children.

Progress in X-linked adrenoleukodystrophy

PURPOSE OF REVIEW

The purpose of this article is to review and evaluate the new information about X-linked adrenoleukodystrophy that has been reported in 2002 and 2003.

RECENT FINDINGS

X-linked adrenoleukodystrophy has two distinct neurological phenotypes: adrenomyeloneuropathy, a non-inflammatory axonopathy mostly in adults, and an intensely inflammatory cerebral myelinopathy mostly in children. The two forms often co-occur in the same family. Heterozygous women and the X-linked adrenoleukodystrophy mouse model often have the adrenomyeloneuropathy phenotype. More than 500 distinct mutations in the defective gene (ABCD1) have been identified, and except in one unique family, do not correlate with the phenotype. Bone marrow transplantation is beneficial in patients with early cerebral involvement. A panel of brain neuroimaging studies aids the selection of patients for bone marrow transplantation. Lorenzo's oil administered to neurologically asymptomatic boys who are less than 6 years old and have a normal magnetic resonance imaging scan appears to reduce the probability of developing neurological abnormalities later in life.

SUMMARY

Progress has been achieved in the delineation of the phenotypes, pathogenesis, diagnosis and prevention of X-linked adrenoleukodystrophy, and therapies are emerging.

Adrenomyeloneuropathy, a dynamic progressive disorder: brain magnetic resonance imaging of two cases

Adrenomyeloneuropathy (AMN) is a phenotype variant of X-linked adrenoleukodystrophy. We present two patients with adult-onset AMN who were initially suspected to have demyelinating disorders radiologically and finally diagnosed on the basis of laboratory data. The brain magnetic resonance images showed abnormal signal intensity at pyramidal tracts and cerebellar hemisphere bilaterally with abnormal enhancement after contrast medium administration. Review of the literature shows that the brain magnetic resonance findings of adrenomyeloneuropathy may include normal brain, tract demyelination, white matter demyelination, or brain atrophy. Disease progression was demonstrated by follow-up imaging.

Hematopoietic cell transplantation for inherited metabolic diseases: an overview of outcomes and practice guidelines

For the past two decades, hematopoietic cell transplantation (HCT) has been used as effective therapy for selected inherited metabolic diseases (IMD) including Hurler (MPS IH) and Maroteaux-Lamy (MPS VI) syndromes, childhood-onset cerebral X-linked adrenoleukodystrophy (X-ALD), globoid-cell leukodystrophy (GLD), metachromatic leukodystrophy (MLD), alpha-mannosidosis, osteopetrosis, and others. Careful pre-HCT evaluation is critical and coordinated, multidisciplinary follow-up is essential in this field of transplantation. The primary goals of HCT for these disorders have been to promote long-term survival with donor-derived engraftment and to optimize the quality of life. Guidelines for HCT and monitoring are provided; a brief overview of long-term results is also presented.