(LKS) probably is not a single entity. In most instances, the cause is unknown. The relative rarity of a focal etiology may explain why the outcome of this disorder generally is much poorer than that of other acquired aphasias of childhood (see van Hout105 for a recent review).
Chronic focal encephalitis
Some cases of LKS may be a form of chronic focal in the tradition of Rasmussen’s encephalitis. However, only one of the few pathologic specimens is consistent with encephalitis, and the case itself had atypical features.106
A few patients with documented structural lesions, including tumors and cysts, have been reported.37,73,95,107–110 Treatment of these lesions has been associated with temporally related improvement of the aphasia. For example, placement of a peritoneal shunt in a patient with a temporal lobe arachnoid cyst resulted in significant metabolic improvement (as evidenced by SPECT) in all cortical regions, especially the inferior frontal gyrus and the perisylvian area. Residual occurred in the left superior temporal gyrus. The patient showed a pronounced increase in word fluency and some progress in verbal auditory comprehension.95 Tumor and cyst removal also has coincided with improved language function. In one patient with a unilateral intrasylvian pacemaker, all activity stopped after a small transection of a sylvian pacemaker. Her auditory agnosia improved, although her speech did not.45
Focal epileptiform activity
Increasingly sophisticated electrophysiologic data suggest activity of focal origin in some patients. () documents that the intrasylvian cortex is the pacemaker of the epileptiform discharge in LKS.44,45 In some patients with a unilateral pacemaker, spread to the contralateral hemisphere is rapid.
Metabolic imaging studies (see below) support a focal origin in a number of cases, even when the abnormalities appear generalized. For example, Park et al.111 reported on an 11-year-old boy with partial seizures and and behavioral regression whose sleep EEG showed continuous spikes and waves during slow sleep (CSWS). His EEG during wakefulness showed epileptiform discharges over the right parietal region, suggesting that the discharges during sleep were a manifestation of secondary bilateral synchrony. After right-sided intracarotid amobarbital injection, the and wave activity was suppressed bilaterally. FDG-PET imaging revealed hypermetabolism in the right superior temporoparietal region.
Patients with CSWS
The metabolic abnormalities in LKS children with CSWS tend to be more extensive than in those without CSWS. Metabolic abnormalities tend to increase in sleep. During metabolic imaging (FDG-PET), patients with CSWS had bitemporal and bifrontal hypometabolism.52
Two patients with CSWS were discussed by Rintahaka et al.117 In the first patient, the awake PET study revealed:
In the second child, the awake interictal PET was normal except for mildly increased relative glucose metabolism in the left inferior temporal cortex.117 The sleep PET study with CSWS in this child showed hypermetabolism in both temporal lobes, although the finding was more pronounced and had a wider distribution in the left temporal cortex.
In normal subjects, PET studies performed during awake and sleep states have not revealed such differences. Whether the temporal lobes are involved in the generation of CSWS remains to be confirmed in a larger group of patients.
Metabolic characteristics of LKS
Maquet et al.30 culled four basic metabolic characteristics of LKS via FDG-PET studies:
Maquet et al.30 hypothesized that the acquired deterioration of cognitive function with CSWS is caused by an alteration of the maturation of one or several associative cortices, primarily involving local interneurons and corticocortical associative neurons. SPECT scanning and steady-state auditory evoked potentials found bitemporal and left frontal pathophysiology in a child with LKS variant responding to corticosteroid treatment.118
Adapted from: Nass R and Gross A. Landau-Kleffner syndrome and its variants. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;79–92.
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