Cognitive deficits and developmental language disorders in patients with malformations of cortical development

Abstract

It is generally accepted that in patients with malformations of cortical development (MCD) the severity of the neurologic and developmental deficiencies is determined by the etiology, localization, and extent of the malformation, as well as by the severity of the associated epilepsy syndrome. Apart from two detailed reports on the occurrence of developmental dyslexia in patients with periventricular nodular heterotopia (Chang et al., 2005, 2007), precise neuropsychological information is available mainly in patients with polymicrogyria (PMG). A first set of studies has addressed the neuropsychological profiles of patients with bilateral perisylvian PMG. In a study of 17 patients with bilateral perisylvian PMG (Montenegro et al., 2001), 7 had bilateral perisylvian PMG limited to the posterior parietal areas, sparing the anterior two-thirds of the sylvian fissure, and 10 had diffuse bilateral perisylvian PMG. In the first group, neurologic examination was normal, seizures were absent, and two had mild dysarthria later in life. In the second group, all had pseudobulbar palsy with or without motor involvement, and seizures were present in four. A second study in 14 patients with bilateral perisylvian PMG (Jansen et al., 2005) showed that exceptionally low intelligence (Full IQ scores <70) was present in <30% of patients, memory abilities were average or low average, frontal lobe function was relatively well preserved, and both receptive and expressive language skills were severely impaired. These findings suggested that the observed cognitive profiles were related to specific areas of cortical dysfunction and not just to global brain dysfunction. This conclusion was supported by a study of six children with bilateral perisylvian PMG (Saletti et al., 2007) in whom mental retardation was related to the extent of cortical malformation, lexical comprehension and verbal production were more compromised than expected from nonverbal intellectual abilities, and lack of verbal language was not compensated by the use of referential gestures. These results suggested that compromised verbal and gestural communication in bilateral perisylvian PMG is not due simply to mental retardation and/or dysarthria but also to dysfunction of the perisylvian areas concerned with the totality of language processing. Care should be taken not to label patients with bilateral perisylvian PMG as mentally retarded, unless proven by detailed neuropsychological studies. Magnetic resonance imaging (MRI) facilitates early diagnosis, which should result in planning for appropriate education, and allow these individuals to develop to their maximum potential. A second set of studies consisted of patients with a diagnosis of developmental language disorder in whom imaging studies had been performed. Brain MRIs were carried out on a 2T scan and included multiplanar reconstructions