Neuroradiological and neurophysiological indices for neurometabolic disorders

Cranial ultrasound in metabolic disorders presenting in the neonatal period: characteristic features and comparison with MR imaging

BACKGROUND AND PURPOSE

Brain imaging is an integral part of the diagnostic work-up for metabolic disorders, and the bedside availability of cranial ultrasonography (cUS) allows very early brain imaging in symptomatic neonates. Our aim was to investigate the role and range of abnormalities seen on cUS in neonates presenting with metabolic disorders. A secondary aim, when possible, was to address the question of whether brain MR imaging is more informative by comparing cUS to MR imaging findings.

MATERIALS AND METHODS

Neonates with a metabolic disorder who had at least 1 cUS scan were eligible. cUS images were reviewed for anatomic and maturation features, cysts, calcium, and other abnormalities. When an MR imaging scan had been obtained, both sets of images were compared.

RESULTS

Fifty-five infants (35 also had MR imaging) were studied. The most frequent findings were in oxidative phosphorylation disorders (21 cUS and 12 MR imaging): ventricular dilation (11 cUS and 6 MR imaging), germinolytic cysts (GLCs; 7 cUS and 5 MR imaging), and abnormal white matter (7 cUS and 6 MR imaging); in peroxisomal biogenesis disorders (13 cUS and 9 MR imaging): GLCs (10 cUS and 6 MR imaging), ventricular dilation (10 cUS and 5 MR imaging), abnormal cortical folding (8 cUS and 7 MR imaging), and lenticulostriate vasculopathy (8 cUS); in amino acid metabolism and urea cycle disorders (14 cUS and 11 MR imaging): abnormal cortical folding (9 cUS and 4 MR imaging), abnormal white matter (8 cUS and 8 MR imaging), and hypoplasia of the corpus callosum (7 cUS and 6 MR imaging); in organic acid disorders (4 cUS and 2 MR imaging): periventricular white matter echogenicity (2 cUS and 1 MR imaging); and in other disorders (3 cUS and 1 MR imaging): ventricular dilation (2 cUS and 1 MR imaging). cUS findings were consistent with MR imaging findings. cUS was better for visualizing GLCs and calcification. MR imaging was more sensitive for subtle tissue signal intensity changes in the white matter and abnormality in areas difficult to visualize with cUS, though abnormalities of cortical folding suggestive of polymicrogyria were seen on cUS.

CONCLUSION

A wide range of abnormalities is seen using cUS in neonatal metabolic disorders. cUS is a reliable bedside tool for early detection of cysts, calcium, structural brain abnormalities, and white matter echogenicity, all suggestive of metabolic disorders.

A forward look at therapy for pediatric movement disorders

The mainstay of current therapy for pediatric movement disorders is oral symptomatic medication, unless a reversible etiology can be found. However, this approach is apt to pale in comparison with innovative strategies on the clinical forefront. Classical pharmacotherapy is restricted by the blood-brain barrier, which prevents access to the brain of potentially therapeutic molecules. Recent developments in molecular biotechnology include antibody-mediated drug release, feedback-responsive delivery systems, carrier-mediated transport, microspheres composed of polymers and liposomes, permeabilizers, and selective delivery to localized sites and vectors. Neuroprotective strategies for delivering neurotrophic factors and antiapoptotic and antioxidant molecules in neurodegenerative disorders are currently under study in clinical trials. Stem cell transplantation has great potential for tissue engineering and also as a carrier for gene therapy, although its use raises complex societal issues. These approaches, together with a plethora of transgenic knockout animal models of neurodegenerative disorders, offer real promise for a previously untreatable group of movement disorders.

Neurological manifestations of organic acid disorders

Neurological manifestations are very common and can be the leading and/or presenting feature in organic acid disorders, sometimes in the absence of metabolic derangement. Review of the time course and presentation of neurological disease in organic acid disorders reveals characteristic clinical findings of ataxia, myoclonus, extrapyramidal symptoms, metabolic stroke and megalencephaly. A group of organic acid disorders presents exclusively with neurological symptoms. These include glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type I), succinic semialdehyde dehydrogenase deficiency (4-hydroxybutyric aciduria), mevalonic aciduria, N-acetylaspartic aciduria (Canavan disease) and L-2-hydroxyglutaric aciduria. As a group these "cerebral" organic acid disorders appear to remain often undiagnosed and their true incidence is much less well-known than that of the "classical" organic acid disorders. Unfortunately, stringent guidelines for a clinical preselection of neuropaediatric patients to be investigated for organic acid disorders cannot be provided. Today, screening for neurometabolic disorders should be as comprehensive as possible and include determinations of amino acids, purines and pyrimidines and markers of peroxisomal function in addition to organic acid analysis.