Diffusion tensor-based imaging reveals occult abnormalities in adrenomyeloneuropathy

[Evaluation of the Accuracy of Relaxation Time Measurements Using 3D-QALAS at 3.0 T MRI and Comparison with 2D-MDME]

PURPOSE

Three-dimensional (3D) quantification using an interleaved Look-Locker acquisition sequence with a T₂ preparation pulse (QALAS) is a quantitative sequence used to measure relaxation times. The accuracy of the relaxation time measurement of 3D-QALAS at 3.0 T and the bias of 3D-QALAS have not yet been assessed. The purpose of this study was to clarify the accuracy of the relaxation time measurements using 3D-QALAS at 3.0 T MRI.

METHODS

The accuracy of the T₁ and T₂ values for 3D-QALAS was evaluated using a phantom. Subsequently, the T₁ and T₂ values and proton density of the brain parenchyma in healthy subjects were measured using 3D-QALAS and compared with those of 2D multi-dynamic multi-echo (MDME).

RESULTS

In the phantom study, the average T₁ value of 3D-QALAS was 8.3% prolonged than that for conventional inversion recovery spin-echo; the average T₂ value for 3D-QALAS was 18.4% shorter than that for multi-echo spin-echo. The in vivo assessment showed that the mean T₁ and T₂ values and PD for 3D-QALAS were prolonged by 5.3%, shortened by 9.6%, and increased by 7.0%, respectively, compared with those for 2D-MDME.

CONCLUSION

Although 3D-QALAS at 3.0 T has high accuracy T₁ value, which is less than 1000 ms, the T₁ value could be overestimated for tissues with it longer than that T₁ value. The T₂ value for 3D-QALAS could be underestimated for tissues with T₂ values, and this tendency increases with longer T₂ values.

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.

Multiparametric in vivo analyses of the brain and spine identify structural and metabolic biomarkers in men with adrenomyeloneuropathy

OBJECTIVE

Progressive myelopathy causes severe handicap in men with adrenomyeloneuropathy (AMN), an X-linked disorder due to ABCD1 pathogenic variants. At present, treatments are symptomatic but disease-modifying therapies are under evaluation. Given the small effect size of clinical scales in AMN, biomarkers with higher effect size are needed. Here we used high-resolution magnetic resonance techniques to identify non-invasive in vivo biomarkers of the brain and spine with high effect sizes.

METHODS

We performed a multiparametric imaging and spectroscopy study in 23 male patients with AMN (age: 44 ± 11) and 23 male controls (age: 43 ± 11) of similar age and body-mass index. We combined (i) macrostructural analyses of the spine, using cross-sectional area (CSA) and magnetization transfer ratio (MTR), (ii) microstructural analyses of the spine and the brain, using diffusion tensor and the newly developed fixel-based analysis, and (iii) advanced metabolic analyses of the spine using metabolite cycling coupled to a semi-LASER sequences.

RESULTS

Macrostructural alterations (decrease in CSA and MTR) were observed in patients at all spinal cord levels studied (C1-T2 for CSA and C1-C5 for MTR) (p < 0.001). Microstructural alterations were observed in the spine and brain on diffusion tensor and fixel-based metrics though the latter showed higher effect sizes. Metabolic alterations were observed in patients as a decreased total N-acetylaspartate/myo-inositol ratio (p < 0.001). Overall, MTR showed the highest effect size.

CONCLUSION

This cross-sectional study supports the use of multiparametric techniques that elucidate the structural, microstructural and metabolic alterations in AMN. These outcome measures should be tested longitudinally and in clinical trials.

Longitudinal diffusion MRI as surrogate outcome measure for myelopathy in adrenoleukodystrophy

Objective

To prospectively determine the potential of diffusion MRI (dMRI) of the cervical spinal cord and the corticospinal tracts in brain as surrogate outcome measure for progression of myelopathy in men with adrenoleukodystrophy, as better outcome measures to quantify progression of myelopathy would enable clinical trials with fewer patients and shorter follow-up.

Methods

Clinical assessment of myelopathy included Expanded Disability Status Scale (EDSS), Severity Scoring System for Progressive Myelopathy (SSPROM), Timed Up-and-Go, and 6-Minute Walk Test. Applied dMRI metrics included fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity.

Results

Data were available for 33 controls and 52 patients. First, cross-sectionally, differences between groups (controls vs patients; controls vs asymptomatic patients vs symptomatic patients) were statistically significant for fractional anisotropy, mean diffusivity, and radial diffusivity in spinal cord and brain corticospinal tracts (effect size 0.31–0.68). Correlations between dMRI metrics and clinical measures were moderate to strong (correlation coefficient 0.35–0.60). Second, longitudinally (n = 36), change on clinical measures was significant after 2-year follow-up for EDSS, SSPROM, and Timed Up-and-Go (p ≤ 0.021, effect size ≤0.14). Change on brain fractional anisotropy and radial diffusivity was slightly larger (p ≤ 0.002, effect sizes 0.16–0.28). In addition, a statistically significant change was detectable in asymptomatic patients using brain dMRI and not using the clinical measures. Change on clinical measures did not correlate to change on dMRI metrics.

Conclusion

Although effect sizes were small, our prospective data illustrate the potential of dMRI as surrogate outcome measure for progression of myelopathy in men with adrenoleukodystrophy.

Overall intact cognitive function in male X-linked adrenoleukodystrophy adults with normal MRI

BACKGROUND

Men with the hereditary peroxisomal disorder X-linked adrenoleukodystrophy (ALD) are at risk of developing inflammatory demyelinating lesions in the brain. In the absence of inflammatory (post-contrast enhancing) lesions on MRI cognitive function is considered spared, but some form of cognitive dysfunction may nevertheless be present. The aim of this cross-sectional study was to characterize cognitive functioning of ALD men with no or minimal MRI abnormalities, which will define cognitive functioning in this category of patients.

METHODS

A neuropsychological battery covering a broad range of cognitive domains, including language, verbal and non-verbal memory, visuoconstruction, executive functioning, and psychomotor speed, was used. Means and proportions of borderline and impaired T scores ≤36 were compared to the standardized norm group and a qualitative case-by-case analysis was performed for participants with T scores ≤36 within ≥2 domains. Patients with MRI abnormalities that were extensive (Loes score > 3) or showed enhancement post-contrast were excluded.

RESULTS

Thirty-three men participated (median age 44 years, range 19-71). Mean performance on verbal fluency was poorer in patients (45.70 ± 8.85 patients vs. 50 ± 10 standardized norm group, p = 0.009), as was the percentage of borderline and impaired scores on visuoconstruction (Beery VMI: 19% patients vs. 8% standardized norm group, p = 0.02; RCFT copy: 81% patients vs. 2% standardized norm group, p < 0.0005) and mental reaction time during a complex decision task (18% patients vs. 8% standardized norm group, p = 0.055). Moreover, 9/33 (27.3%) patients had T scores ≤36 within ≥2 domains.

CONCLUSIONS

Given the heterogeneous pattern of mostly borderline scores cognitive functioning seems not impaired in the vast majority of adult ALD males with no or minimal MRI abnormalities. However, borderline to impaired cognitive dysfunction was present in 27.3%, with the majority being borderline scores. Longitudinal studies will have to determine if this reflects early cerebral disease under the detection limit of MRI.

Therapeutic strategies in adrenoleukodystrophy

Adrenoleukodystrophy (ALD) is an X‑linked hereditary disorder due to mutations of the ABCD1 gene, which encodes a peroxisomal transport protein necessary for very long-chain fatty acid degradation (VLCFA). Toxic accumulation thereof is associated with a proinflammatory state and eventual cell death in multiple tissues. ALD may manifest either as a fatal, rapidly progressive demyelinating disease in boys and adult men, or as a slowly progressive adult-onset long-tract myelopathy along with peripheral neuropathy. Our understanding of manifold mechanisms implicated in the disease pathology is currently incomplete, as neither genotype-phenotype correlation nor the trigger for cerebral disease has been described. Therapy objectives are therefore broadly aimed at correcting either the gene mutation or downstream molecular effects, such as oxidative stress. Advancements in disease detection, including the newly implemented newborn screening in the US and imaging modalities, allow for more timely intervention in the form of hematopoietic stem cell transplantation (HSCT), which may only be performed in early cerebral disease states.

Quantitative microstructural deficits in chronic phase of stroke with small volume infarcts: A diffusion tensor 3-D tractographic analysis

BACKGROUND

Non-infarct zone white matter wallerian degeneration is well-documented in large volume territorial infarctions. However to what extent these abnormalities exist in small volume infarction is not known, particularly since routine T2/FLAIR MR images show minimal changes in such cases. We therefore utilized DTI based quantitative 3D tractography for quantitative assessment of white matter integrity in chronic phase of small volume anterior circulation infarcts.

METHODS

Eleven chronic stroke subjects with small anterior circulation large vessel infarcts (≤10cm(3) volume of primary infarct) were compared with 8 age matched controls. These infarcts had negligible to mild gliosis and encephalomalacia in the primary infarct territory without obvious wallerian degeneration on conventional MRI. Quantitative Diffusion Tensor 3-D tractography was performed for CST, genu and splenium of corpus callosum. Tract based Trace and fractional anisotropy (FA) were compared with age matched controls.

RESULTS

On univariate analysis, Chronic stroke subjects had significant elevation in Trace measurement in genu of corpus callosum (GCC), ipsilesional and contralesional CST, (p<0.05), compared to controls. After adjusting for smoking, hypertension (HTN) and non-specific white matter hyperintensities, (WMHs), there was significant elevation in trace within the ipsilesional CST (p=0.05). Contralesional CST FA correlated significantly with walking speed, r=0.67, p=0.03.

CONCLUSIONS

Stroke subjects with small volume infarcts demonstrate significant quantitative microstructural white matter abnormalities in chronic phase, which are otherwise subthreshold for detection on routine imaging. Ability to quantify these changes provides an important marker for assessing non-infarct zone neuroaxonal integrity in the chronic phase even in the setting of small infarction.

Imaging manifestations of the leukodystrophies, inherited disorders of white matter

The leukodystrophies are a diverse set of inherited white matter disorders and are uncommonly encountered by radiologists in everyday practice. As a result, it is challenging to recognize these disorders and to provide a useful differential for the referring physician. In this article, leukodystrophies are reviewed from the perspective of 4 imaging patterns: global myelination delay, periventricular/deep white matter predominant, subcortical white matter predominant, and mixed white/gray matter involvement patterns. Special emphasis is placed on pattern recognition and unusual combinations of findings that may suggest a specific diagnosis.

X-linked adrenoleukodystrophy (X-ALD): clinical presentation and guidelines for diagnosis, follow-up and management

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. The disease is caused by mutations in the ABCD1 gene that encodes the peroxisomal membrane protein ALDP which is involved in the transmembrane transport of very long-chain fatty acids (VLCFA; ≥C22). A defect in ALDP results in elevated levels of VLCFA in plasma and tissues. The clinical spectrum in males with X-ALD ranges from isolated adrenocortical insufficiency and slowly progressive myelopathy to devastating cerebral demyelination. The majority of heterozygous females will develop symptoms by the age of 60 years. In individual patients the disease course remains unpredictable. This review focuses on the diagnosis and management of patients with X-ALD and provides a guideline for clinicians that encounter patients with this highly complex disorder.

Diffusion-weighted Magnetic Resonance Imaging in the Early Diagnosis of Neonatal Adrenoleukodystrophy

A newborn baby girl developed seizures right after birth. On the fourth day, the baby was examined using diffusion sequence magnetic resonance imaging (MRI) and diagnosed to have neonatal adrenoleukodystrophy. Laboratory findings confirmed the diagnosis. This is the first case of neonatal adrenoleukodystrophy (NALD) where diffusion MRI sequence helped in the diagnosis. We find association of NALD with seizures at birth is an extremely rare occurrence, and so far, only one case has been mentioned in the literature.

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.

Leukoencephalopathies and metabolic diseases

Leukoencephalopathies and metabolic diseases comprise a great number of heterogeneous disorders. Diagnosis of these disorders may be challenging at times, requiring sophisticated laboratory investigations. Magnetic resonance imaging (MRI) is useful in supporting diagnosis even though it bears problems of specificity. Quantitative MRI techniques, providing information on cerebral metabolites and tissue microstructure within and outside visible lesions, have proven to be important for understanding the pathogenic mechanisms leading to tissue damage and monitoring disease evolution and response to treatment. This has prompted a more extensive use of these techniques in the clinical setting as a complement to the traditional MRI.

Quantitative diffusion tensor analysis using multiple tensor ellipsoids model and tensor field interpolation at fiber crossing

RATIONALE AND OBJECTIVES

In regions of intravoxel fiber crossing, the single-tensor model does not provide accurate results. The previously published models could resolve this issue but needed a long scan time and long computational time. This article aims to present the new model, which uses interpolated diffusion tensor orientations and requires the estimation of fewer parameters than the previously published model, where all parameters for the two diffusion ellipsoids have to be estimated.

MATERIALS AND METHODS

Fiber orientation information was reconstructed by using the radial basis function-based interpolation technique from tensor information in given seed regions of interest. Synthetic phantom data were generated, and the proposed method was compared with the conventional two-ellipsoid method. Data from one normal volunteer were analyzed to determine the effectiveness of the proposed method. The number of parameters to be estimated could be reduced by using the estimated fiber orientation information so that diffusion parameter calculation at fiber crossing becomes robust.

RESULTS

The human study showed that fractional anisotropy (FA) values estimated by the proposed method (FA = 0.67 for the corpus callosum, 0.65 for the corticospinal tract) were significantly higher than that estimated by the standard single-tensor-based method (FA = 0.35), and the estimated FA value showed good agreement with the FA value in the adjacent fiber bundle.

CONCLUSION

The proposed radial basis function-based technique could reconstruct diffusion properties at the fiber-crossing volume from sparse sampling of high angular diffusion weighted images.

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.

The neuropsychiatry of adrenomyeloneuropathy

BACKGROUND

While the adult form of adrenoleukodystrophy (ALD) has been associated with an elevated rate of affective disturbance, the myeloneuropathic form of the disease known as adrenomyeloneuropathy (AMN) has been associated with only occasional cases of major mental illness. Given that cerebral involvement occurs in up to half of AMN sufferers, we hypothesized that rates of mental illness may match those with adult ALD.

OBJECTIVE

To describe the psychiatric, cognitive, and disability variables in a sample of Australian AMN sufferers.

METHODS

Ten genetically confirmed AMN sufferers underwent diagnostic psychiatric interview (Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Axis I Disorders), rating scales of psychiatric disturbance (Brief Psychiatric Rating Scale, Hospital Anxiety and Depression Scale, Beck Depression and Anxiety Inventories, and Short-Form 36), and cognitive function (the Neuropsychiatry Unit Cognitive Assessment Tool and Mini-Mental State Examination).

RESULTS

While the group as a whole was generally cognitively intact, it demonstrated a higher than expected prevalence of lifetime and current major affective illness. Current symptom levels were low at the time of study participation. Psychopathology did not relate to adrenal status, nor to level of physical or functional impairment.

CONCLUSION

This small sample suggests that the level of psychiatric morbidity in AMN patients is elevated, and the rate of affective disturbance approaches those of adult ALD sufferers. This may reflect that AMN is not a "pure" myeloneuropathy, and that mild cerebral involvement may be associated with affective illness.

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.

Auditory brainstem response findings and peripheral auditory sensitivity in adrenoleukodystrophy

Measurements of the auditory brainstem response (ABR) were obtained in 96 individuals with X-linked adrenoleukodystrophy (X-ALD). The patients were divided into five diagnostic groups on the basis of neurologic diagnosis. The five groups were cerebral childhood and adolescent, pure adrenomyeloneuropathy (pure AMN), adrenomyeloneuropathy cerebral (AMN cerebral), Addison's only and symptomatic female heterozygotes. Results indicated the presence of marked ABR abnormalities for all groups most frequently involving Wave V, followed by Wave III and Wave I. Abnormalities of all interpeak latency intervals (i.e., I-III, III-V and I-V) were observed for all groups. ABR abnormalities were most frequently seen in the AMN-cerebral and pure AMN groups but were also common in the symptomatic female heterozygote group. The ABRs in the cerebral childhood and adolescent group were the least impaired of the five groups examined. Age was found to be a significant independent predictor of bilateral ABR abnormalities but VLCFA levels, MRI Loes score, and duration of symptoms were not found to be independent predictors of bilateral ABR abnormalities after adjusting for ALD phenotype. Patients with AMN were significantly more likely to have bilateral ABR abnormalities than the cerebral childhood and adolescent group after adjusting for age, duration of symptoms, EDSS score, VLCFA levels and MRI Loes scores. The prevalence of peripheral hearing loss was not found to exceed that present in age and sex matched normal control groups derived from the NHANES (1999-2000), indicating a lack of association between peripheral hearing loss and X-linked adrenoleukodystrophy. It was concluded that: (1) auditory sensitivity in X-ALD is not significantly impaired; (2) ABR abnormalities are a frequent finding and may be caused by abnormalities of fiber tracts in the region of the lateral lemniscus and inferior colliculus; and, (3) the abnormalities progress slowly and appear to be associated mainly with the AMN phenotype.