Age dependence of diffusion-weighted magnetic resonance imaging findings in maple syrup urine disease encephalopathy

A patient with maple syrup urine disease (MSUD) who developed encephalopathy twice and underwent magnetic resonance examinations, including diffusion-weighted (DW) imaging, is presented. Areas of abnormal intensity on DW images dramatically differed between the initial and second attacks, apparently attributable to the difference in myelination. Our observation demonstrates the age dependence of DW imaging findings in MSUD encephalopathy attributable to progression of myelination and would help in the proper diagnosis of MSUD encephalopathy at any age.

Diffusion-weighted MR imaging in leukodystrophies

Leukodystrophies are genetically determined metabolic diseases, in which the underlying biochemical abnormality interferes with the normal build-up and/or maintenance of myelin, which leads to hypo- (or arrested) myelination, or dysmyelination with resultant demyelination. Although conventional magnetic resonance imaging has significantly contributed to recent progress in the diagnostic work-up of these diseases, diffusion-weighted imaging has the potential to further improve our understanding of underlying pathological processes and their dynamics through the assessment of normal and abnormal diffusion properties of cerebral white matter. Evaluation of conventional diffusion-weighted and ADC map images allows the detection of major diffusion abnormalities and the identification of various edema types, of which the so-called myelin edema is particularly relevant to leukodystrophies. Depending on the nature of histopathological changes, stage and progression gradient of diseases, various diffusion-weighted imaging patterns may be seen in leukodystrophies. Absent or low-grade myelin edema is found in mucopolysaccharidoses, GM gangliosidoses, Zellweger disease, adrenomyeloneuropathy, L-2-hydroxyglutaric aciduria, non-ketotic hyperglycinemia, classical phenylketonuria, Van der Knaap disease and the vanishing white matter, medium grade myelin edema in metachromatic leukodystrophy, X-linked adrenoleukodystrophy and HMG coenzyme lyase deficiency and high grade edema in Krabbe disease, Canavan disease, hyperhomocystinemias, maple syrup urine disease and leukodystrophy with brainstem and spinal cord involvement and high lactate.

Diagnostic value of diffusion-weighted magnetic resonance imaging in pediatric cerebral diseases

The purpose of this study was to detect the diagnostic value of diffusion-weighted magnetic resonance imaging in different pediatric cerebral diseases involving the cerebral white and gray matter and to compare the diffusion properties with age-matched normal children. Conventional and diffusion-weighted magnetic resonance imaging were performed in 21 children with various neurologic disorders and 25 normal control subjects. Apparent diffusion coefficients were measured from the brain lesions and 12 normal-appearing white and gray matter areas in the study group. Twelve normal-appearing areas were also measured in the control group. Apparent diffusion coefficient values obtained from the normal subjects were similar to values described in the literature but were significantly different from the control subjects. Apparent diffusion coefficient values for the neurodegenerative disease group (n = 8), the anoxic encephalopathy group (n = 4), the subacute sclerosing panencephalitis group (n = 4), the acute disseminated encephalomyelitis group (n = 3), and the encephalitis group (n = 2) were respectively between 0.29-1.85 x 10(-5) cm2/s, 0.13-1.87 x 10(-5) cm2/s, 0.96-1.57 x 10(-5) cm2/s, 0.49-0.73 x 10(-5) cm2/s, and 0.42-1.50 x 10(-5) cm2/s. Although this study is limited because of the size of the patient sample and disease heterogeneity, diffusion-weighted magnetic resonance imaging provides useful and complementary information regarding the degree of involvement in different pediatric neurologic disorders.

Leucine toxicity in a neuronal cell model with inhibited branched chain amino acid catabolism

Individuals with the inborn error of metabolism, maple syrup urine disease (MSUD), are identified by newborn screening programs and treated with protein-modified diets that allow near normal growth and development. However, regardless of cause, a protein insult leads to metabolic decompensation, resulting in brain cell damage. The mechanism responsible for the damage is not well characterized due, in part, to the lack of an appropriate experimental model system with impaired branched chain alpha-ketoacid dehydrogenase (BCKD) activity. Here, we describe the construction of a rat pheochromocytoma cell (PC12) model harboring a doxycycline-controlled BCKD-kinase transgene. When BCKD-kinase is over-expressed in these cells, the endogenous BCKD activity is decreased, blocking branched chain amino acid (BCAA) catabolism. In cells over-expressing BCKD-kinase, addition of 25 mM leucine to the medium results in cell death. This experimental cell model accurately mimics the neuronal dysfunction in maple syrup urine disease and should facilitate further understanding of the pathophysiology of this disease and neuronal cell branched chain amino acid metabolism in general.

Maple syrup urine disease encephalopathy: a follow-up study in the acute stage using diffusion-weighted MRI

Neonatal maple syrup urine disease (MSUD) is associated with diffuse oedema and characteristic MSUD oedema. We present a newborn infant with two coexisting different types of oedema. The myelinated white matter showed a marked decrease in the water apparent diffusion coefficient (ADC) compatible with cytotoxic oedema. The unmyelinated white matter showed an increase in ADC, consistent with vasogenic-interstitial oedema. On follow-up studies, the cytotoxic oedema showed improvement, but the vasogenic-interstitial oedema progressed into brain atrophy.

Maple Syrup Urine Disease

We present conventional magnetic resonance (MR) imaging with diffusion-weighted and diffusion-tensor imaging findings in a 10-day-old neonate with maple syrup urine disease (MSUD). On conventional MR imaging, signal abnormalities were noted in the affected white matter of cerebellum, dorsal brainstem, thalami, posterior limbs of internal capsules, and the corona radiata. These regions showed marked hyperintensity on diffusion-weighted images with decreased apparent diffusion coefficient values (average 68% reduction). Diffusion-tensor imaging showed decreased anisotropy (average 57% reduction) in the corresponding areas. Both diffusion-weighted and diffusion-tensor imaging are valuable in the diagnosis and understanding of the pathogenesis of MSUD, with findings that suggest cytotoxic edema and damaged oligodendro-axonal units within the affected white matter.

MRI of Neonatal Encephalopathy

We present the magnetic resonance imaging (MRI) findings in neonatal encephalopathy, including hypoxic-ischaemic encephalopathy, perinatal/neonatal stroke, metabolic encephalopathy from inborn errors of metabolism, congenital central nervous system infections and birth trauma. The applications of advanced MRI techniques, such as diffusion-weighted imaging and magnetic resonance spectroscopy are emphasized.

Infantile hypermethioninemia and hyperhomocysteinemia due to high methionine intake: a diagnostic trap

Studies were carried out to identify the cause of combined severe hypermethioninemia and moderate hyperhomocysteinemia in a cluster of 10 infants ascertained between 1999 and early 2001. Although several were thought initially to have cystathionine beta-synthase (CBS) deficiency and treated accordingly, CBS deficiency and other known genetic causes of hypermethioninemia were ruled out by assay of CBS activity in fibroblasts of four patients and by assays of plasma cystathionine and S-adenosylmethionine. Retrospective data on dietary methionine intakes and plasma concentrations of methionine and related metabolites established that the hypermethioninemia in nine of the 10 babies was related to ingestion of an infant protein hydrolysate formula, the methionine content of which had been increased from May 1998 to February 2001. The formula in question has now been reformulated and is no longer available. The 10th infant manifested similar metabolic abnormalities while receiving TPN containing excessive methionine. Brain MRI abnormalities indicative of cerebral edema, most marked in the cerebral cortex and posterior brainstem, occurred in two patients near times of extreme hypermethioninemia. Metabolic and MRI abnormalities resolved when the methionine intake decreased. A third infant had a normal MRI 1 day after the formula was changed. The possible relationship between extreme hypermethioninemia and cerebral edema is discussed and a working hypothesis offered to explain the relative sensitivity of the inferior colliculi, based upon the facts that this is the region most active in glucose utilization and that Na(+),K(+)-ATPase is inhibited by methionine and related metabolites.

Diffusion-weighted imaging in the assessment of neurological damage in patients with methylmalonic aciduria

Diffusion-weighted magnetic resonance imaging (DW-MRI) of the brain was performed in two patients with methylmalonic aciduria who presented signs and symptoms of neurological involvement without metabolic decompensation. Patient 1 presented acute metabolic stroke and patient 2 presented subacute encephalopathy. Brain DW-MRI confirmed very recent damage in patient 1, while the absence of brain lesions on brain DW-MRI indicates the development of more chronic damage in patient 2. Brain DW-MRI represents an additional and complementary tool in the assessment of brain damage in methylmalonic aciduria patients who develop neurological syndrome.