Imaging of neurogenetic and neurometabolic disorders of childhood

Expanding Role of Proton Magnetic Resonance Spectroscopy: Timely Diagnosis and Treatment Initiation in Partial Ornithine Transcarbamylase Deficiency

We report the case of a 3-year-old male patient who presented with a 3-day history of altered mental status, emesis, and abdominal pain in the setting of a viral illness. A rapid screening revealed a high ammonia level and after reviewing his proton magnetic resonance spectroscopy (1H MRS) which showed the classic triad of high glutamate, low choline, and myoinositol, a diagnosis of ornithine transcarbamylase deficiency (OTCD) was made within 6 hours of presentation. Therapy with sodium phenylbutyrate and sodium benzoate was initiated and patient was discharged after 3 days with no neurologic disability. Biochemical and molecular testing eventually confirmed the diagnosis. 1H MRS is a practical and fast neuroimaging modality that can aid in diagnosis of OTCD and enables faster initiation of treatment in acute settings.

Apparent Diffusion Coefficient Value Changes and Clinical Correlation in 90 Cases of Cytomegalovirus-Infected Fetuses with Unremarkable Fetal MRI Results

BACKGROUND AND PURPOSE

Cytomegalovirus is the leading intrauterine infection. Fetal MR imaging is an accepted tool for fetal brain evaluation, yet it still lacks the ability to accurately predict the extent of the neurodevelopmental impairment, especially in fetal MR imaging scans with unremarkable findings. Our hypothesis was that intrauterine cytomegalovirus infection causes diffusional changes in fetal brains and that those changes may correlate with the severity of neurodevelopmental deficiencies.

MATERIALS AND METHODS

A retrospective analysis was performed on 90 fetal MR imaging scans of cytomegalovirus-infected fetuses with unremarkable results and compared with a matched gestational age control group of 68 fetal head MR imaging scans. ADC values were measured and averaged in the frontal, parietal, occipital, and temporal lobes; basal ganglia; thalamus; and pons. For neurocognitive assessment, the Vineland Adaptive Behavior Scales, Second Edition (VABS-II) was used on 58 children in the cytomegalovirus-infected group.

RESULTS

ADC values were reduced for the cytomegalovirus-infected fetuses in most brain areas studied. The VABS-II showed no trend for the major domains or the composite score of the VABS-II for the cytomegalovirus-infected children compared with the healthy population distribution. Some subdomains showed an association between ADC values and VABS-II scores.

CONCLUSIONS

Cytomegalovirus infection causes diffuse reduction in ADC values in the fetal brain even in unremarkable fetal MR imaging scans. Cytomegalovirus-infected children with unremarkable fetal MR imaging scans do not deviate from the healthy population in the VABS-II neurocognitive assessment. ADC values were not correlated with VABS-II scores. However, the lack of clinical findings, as seen in most cytomegalovirus-infected fetuses, does not eliminate the possibility of future neurodevelopmental pathology.

Neurodegenerative disorders and metabolic disease

Most genetic causes of neurodegenerative disorders in childhood are due to neurometabolic disease. There are over 200 disorders, including aminoacidopathies, creatine disorders, mitochondrial cytopathies, peroxisomal disorders and lysosomal storage disorders. However, diagnosis can pose a challenge to the clinician when patients present with non-specific problems like epilepsy, developmental delay, autism, dystonia and ataxia. The variety of specialist tests involved can also be daunting. This review aims to give a practical approach to the investigation and diagnosis of neurometabolic disease from the neonatal period to late childhood while prioritising disorders where there are therapeutic options. In particular, patients who have a complex clinical picture of several neurological and non-neurological features should be investigated.

Use of amplitude integrated electroencephalography (aEEG) in patients with inborn errors of metabolism - a new tool for the metabolic geneticist

Patients with metabolic disorders often, especially as newborns, present with encephalopathy and seizures, frequently requiring intensive care during metabolic crises. Cerebral function monitoring using amplitude integrated electroencephalography (aEEG) can be utilized to supplement clinical assessment and other monitoring already in use in the intensive care setting. In this technique, a one or two-channel EEG tracing is obtained, processed, compressed and displayed. Use of aEEG is well established in evaluation and treatment of newborns with hypoxic ischemic encephalopathy. The basis of aEEG interpretation is the recognition of patterns which have been defined for different degrees of encephalopathy. Seizures are identified on the compressed tracing in combination with analysis of the corresponding raw EEG tracing. This review discusses the experience, although limited at this time, with use of aEEG in infants with inborn errors of metabolism. Through an international collaborative, the International Registry for Cerebral Function Monitoring in Patients with Genetics Disorders and Brain Malformations, aEEG tracings of patients with inborn errors of metabolism were collected. The features of 25 traces are included in this review. This collection includes patients with hyperammonemia (HA, n=4), disorders of energy metabolism (DEM, n=9), disorders of amino and organic acid metabolism (DAOAM, n=7), and peroxisomal disorders (PD, n=5). Fifteen of 25 patients demonstrated encephalopathic changes, including patients with HA, DEM and DAOAM, but not PD. In 15 of 25 patients seizure potentials were identified. In HA, DEM, and DAOAM both encephalopathy and seizures may coincide, while in peroxisomal disorders seizures were seen without background patterns indicating encephalopathy, likely due to neuronal migration defects as the underlying cause. The current experience with the use of aEEG in these patients, while limited, indicates that cerebral function monitoring techniques have a role in treatment of patients with metabolic disorders, especially during metabolic crises. Use of aEEG in this patient group is encouraged if locally available, and collaborative efforts to collect data on aEEG use in patients with metabolic disorders are encouraged to further define the scope and utility of this procedure.

Seizures and metabolic disease

Seizures represent an important clinical manifestation of inborn errors of metabolism. The presence of myoclonic seizures and very early onset are clues to a metabolic disorder. Specific correlations between age of seizure onset and electroencephalogram patterns with inborn errors of metabolism are discussed. The explosion of information in neurogenetics and metabolism mandates increasing awareness of appropriate metabolic diagnostic and therapeutic strategies in the setting of certain epilepsies. Specific laboratory, imaging, and treatment considerations are included to present updated material in a field that continues to expand rapidly.