Human herpesvirus 6 encephalopathy predominantly affecting the frontal lobes

Isolated cases of human herpesvirus 6 encephalopathy have recently been reported, although the pathophysiology remains largely unknown. To elucidate the changes specific to human herpesvirus 6 encephalopathy on diagnostic images, this study investigated magnetic resonance imaging findings in 10 patients with a diagnosis of human herpesvirus 6 encephalopathy including diffusion-weighted imaging in 6 of 10, and findings of cerebral blood flow imaging by single-photon emission computed tomography in 9 of 10 patients. No abnormalities were evident on T(1)-weighted, T(2)-weighted, or fluid-attenuated inversion-recovery magnetic resonance imaging during acute phases; however, diffusion-weighted imaging indicated abnormal hyperintensity in the subcortical white matter of the frontal lobes in all six patients during the acute phase. Cerebral blood flow single-photon emission computed tomography revealed decreased perfusion, predominantly in the frontal region of all nine patients during their clinical course. Disturbances predominantly affecting the frontal lobes (region) on magnetic resonance imaging and cerebral blood flow single-photon emission computed tomography were common in all patients, suggesting that the findings may be characteristic of human herpesvirus 6 encephalopathy.     

Acute infantile encephalopathy predominantly affecting the frontal lobes (AIEF): a novel clinical category and its tentative diagnostic criteria

Acute infantile encephalopathy predominantly affecting the frontal lobes (AIEF) is proposed as a novel form of acute encephalopathy in infancy. To establish the diagnostic criteria for AIEF, we reviewed the clinical data of 10 patients who were seen by us and diagnosed as having AIEF, and those of 7 patients in the literature compatible with the diagnosis of AIEF. The mean age of onset was 1 year and 7 months. Boys and girls were equally affected. There is always an association with hyperpyrexia due to viral illness. Manifestations at the onset were convulsive status epilepticus and prolonged coma followed by signs of frontal lobe dysfunction such as a lack of spontaneity and regression of verbal functions. Imaging studies demonstrated edematous changes of the bilateral frontal lobes, which showed increased cerebral perfusion initially but attenuated perfusion several weeks later. The recovery of intellectual deficit was generally slower than that of motor disability. Based on these findings, we propose tentative diagnostic criteria of AIEF.     

Epilepsy and the frontal lobes

Although the frontal lobes contain a large proportion of the total cerebral cortex in human brain, the epilepsies arising in this region are less studied and less well characterised than epilepsies arising in the mesial temporal lobe. Detailed studies of seizure semiology have identified a number of patterns of frontal lobe seizure, but with inconsistency across studies, and with limited evidence that specific patterns arise in specific discrete frontal lobe regions. In contrast to mesial temporal lobe epilepsy, there is no consistent pattern of cognitive impairment seen in patients with frontal lobe epilepsy, although some evidence exists to support the notion that cognitive function may be impaired. Given the rich interconnectivity between frontal lobes and many other brain regions, it is not surprising to find functional deficits in the frontal lobes in patients with epilepsy arising in other sites; this is best studied in patients with temporal lobe epilepsy. Current concepts in epilepsy suggest that epilepsies hitherto regarded as idiopathic generalised (rather than focal) may in fact have a focal origin of seizure activity; this may be supported by increasing evidence for focal structural and functional frontal lobe abnormalities in idiopathic generalised epilepsies.     

Behavioural conditions affecting saccadic eye movements elicited electrically from the frontal lobes of primates.

We assessed the effects of varying the time at which electrical stimulation was delivered to the dorsomedial frontal cortex (DMFC) and the frontal eye fields (FEF) relative to the onset of a visual target. Monkeys were required to fixate the visual target to obtain a drop of apple juice as reward. We found that the probability of eliciting saccades increased with increases in the delay of electrical stimulation relative to target onset. Also, the current threshold to evoke saccades decreased as electrical stimulation was delivered later following target onset. There were major differences in the magnitude of this effect with stimulation of the DMFC versus the FEF. The current threshold to evoke saccades from the DMFC was 16 times greater when electrical stimulation was delivered 200 ms after target onset as compared to when it was delayed 200 ms after target offset. In contrast, the current threshold to evoke saccades from the FEFs was only three times greater when stimulation was delivered under similar conditions. These results suggest that the FEF are more closely connected with the saccade generator for the execution of saccadic eye movements than is the DMFC, even though both regions have direct projections to brainstem oculomotor centres.     

Symmetric syphilitic gummas of the frontal lobes

Summary An anatomo-clinical observation of symmetrical syphilitic gummas in the frontal lobes is described and some problems related to the endocranial localization of syphilitic gummas are reviewed.The difficulty establishing a differential clinical diagnosis between cerebral syphilitic gumma and other intracranial neoformations is discussed. Neuro-surgical intervention is still essential for a syphilitic gumma.Tentative specific medical treatment is usually ineffective and entails serious risks. Post-operative specific medical treatment (following histological confirmation) is recommended since parenchymal inflammation and syphilitic arteritis can be improved.     

Subjective ordering, short-term memory, and the frontal lobes

Four tasks relying on short-term retention, i.e. digit span, missing scan, randomization span, and pointing span were presented to patients with frontal-lobe lesions and normal controls. Digit span was considered a measure of passive short-term memory, the other three tasks additionally reflect comparing processes, and two of these, the randomization and pointing spans, also measure active ordering by the subject. The results confirmed Petrides and Milner's (Neuropsychologia 20, 249-262, 1982) hypothesis that frontal-lobe patients are typically deficient in subject-ordered tasks. It is also suggested that they are deficient in a spontaneous generation, rather than comparison component of subjective ordering.