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  • 1
    ISSN: 1432-1076
    Keywords: Phenylketonuria ; Myelination ; Magnetic resonance imaging ; 1H spectroscopy ; T2 relaxometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to further clarify the pathogenesis and clinical significance of MRI white matter abnormalities in treated hyperphenylalaninaemia (HPA), ten patients (seven type I HPA, two type II and one type III) underwent T2 relaxometry (n=8) and/or1H spectroscopy (n=7) in addition to conventional MR spin-echo imaging at 1.5 T. Two patients with severe MRI abnormalities had repeat examinations during and after a 6-to 8-month period of strict diet control. The clinical evaluation included a detailed neurological examination. In nine out of ten patients visual evoked potentials (VEP) were obtained parallel to the MR examination. MR imaging demonstrated typical symmetrical areas of prolonged T2 relaxation time predominantly in the posterior periventricular white matter in all but one of type I and II patients. There was no consistent relationship between MRI findings and time of diagnosis/initiation of therapy, IQ or visual evoked potential changes. MRI abnormalities tended to be more severe in patients with poor dietary control and high current plasma phenylalanine levels, whereas a normal MRI was found only in patients with plasma phenylalanine levels continuously below 0.36 mmol/l. There was marked regression of MRI abnormalities already after 3 months of strict diet control. T2 relaxometry showed a bi-exponential behaviour of T2 in the affected white matter, with a slow component of about 200–450 ms, indicating an increase in free (extracellular) water.1H spectroscopy revealed no signs of severe neuronal damage. We conclude, that the observed white matter changes in treated HPA probably represent reversible structural myelin changes rather than permanent demyelination.
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  • 2
    ISSN: 1432-1076
    Keywords: Phenylketonuria ; Adolescents ; Magnetic resonance imaging ; Myelination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cranial magnetic resonance imaging (MRI) was performed in nine treated adolescents with hyperphenylalaninaemia (HPA) in order to analyse possible changes in myelination. Three patients suffered from type I HPA, four from type II and two from type III (persistent HPA). Images were obtained with a 1.5T unit using spin-echo-sequences. In all patients with type I or type II HPA, abnormal findings in the cerebral white matter were demonstrated including band-like and/or confluent patchy areas of high signal intensity predominantly in the peritrigonal region, with anterior and posterior periventricular extension and/or involvement of the subcortical white matter. The extent of MRI changes did not correlate with the initiation, duration or quality of dietary treatment. There was also no consistent relationship between electrophysiological changes and white matter abnormalities on MRI. Our findings suggest a disturbance of myelination in patients with treated HPA. These results correspond well with earlier neuropathological and biochemical studies in untreated patients.
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  • 3
    ISSN: 1432-1076
    Keywords: Key words Hyperphenylaninaemia ; Phenylketonuria ; Evoked potentials ; Metabolic disorders ; Dopamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We performed studies of multimodal evoked potentials and peripheral sensory and motor nerve conductions in 33 early and 6 late treated patients with phenylketonuria. The studies revealed the following picture: 1. In 27% of early treated patients latencies of visual evoked potentials were increased. The cause for these changes is unknown. 2. Nerve conduction studies showed the presence of a minor sensory neuropathy which in rare cases may also affect peripheral motor nerves. This neuropathy did not have features of a central-peripheral distal axonopathy which argues against a toxic/nutritional causation. 3. Deficits in the central sensory, motor, and auditory pathways were present, but rare in early treated patients. If the results of electrophysiological studies reported by different groups are compared, the emerging picture is very similar and the majority of the – minor – differences is likely to be explained by technical aspects.
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  • 4
    ISSN: 1432-1459
    Keywords: Key words Corpus callosum ; Corticospinal tract ; Phenylketonuria ; Focal transcranial magnetic brain ; stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The transcranial activation and the conduction properties of corticospinal and callosal neurons were investigated in 12 early-treated adolescents (aged 17.3, SD 3.5 years; range 14–27 years) with phenylketonuria (PKU) by focal transcranial magnetic stimulation (fTMS) of the motor cortex. The patients had no functionally relevant motor disturbances in daily life or on clinical testing. Corticospinally mediated excitatory (response thresholds, amplitudes, central motor latencies) and inhibitory [duration of postexcitatory inhibition (PI)] effects of fTMS were investigated in contralateral hand muscles. Transcallosal inhibition (TI) (onset latency, duration, transcallosal latency) of tonic electromyographic (EMG) activity was tested in ipsilateral muscles. Peripheral motor latencies were determined for responses elicited by magnetic stimulation over cervical nerve roots. Ten normal subjects served as controls. Since in all PKU patients, central and peripheral motor latencies were normal, no neurophysiological indication of a demyelination of corticospinal or peripheral motor fibres was found. However, cortical thresholds of corticospinally mediated responses were increased (52.1, SD 11.6% versus 35.0, SD 7.4% of maximum stimulator output; P 〈 0.05; n = 24 hands) and their amplitudes reduced (2.9, SD 1.4 mV versus 6.1, SD 1.5 mV, P 〈 0.05). The duration of PI was shortened (132, SD 53 ms versus 178, SD 57 ms; P 〈 0.05). TI was absent in 37.5% of the investigated hands or tended to be weak. When TI was present, its onset latencies (38.0, SD 3.6 ms versus 34.7, SD 3.3 ms) and transcallosal latencies were prolonged (18.5, SD 3.8 ms versus 14.8, SD 3.2 ms), while its duration was normal. These abnormal excitatory and inhibitory effects of fTMS suggest a reduced susceptibility of cortical excitatory and inhibitory neuronal structures compatible with a loss of neurons or a rarefication of their dendrites.
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