Specific language disorders: their diagnosis, classification and study using magnetoencephalography
Specific language disorder (SLD) is defined as a disorder in which language is slow and retarded with respect to the patient's chronological age, and which is not related to a sensory-auditory or motor deficit or to a pervasive development disorder; in other words, structural and functional neurological developmental disorders must be excluded. After many studies and attempts to reach an agreement, specific language disorders have been broadly classified into two groups: specific expressive language disorder and specific receptive-expressive language disorder. Our objective was to study SLD using magnetoencephalography (MEG) in order to look for epileptiform manifestations in precise language areas. We studied a sample made up of 11 patients with SLD, one of whom had Landau-Kleffner syndrome and one with cryptogenic-type SLD. The criteria used were age-dependent autism exclusion tests and specific language tests for SLD. The MSI technique was carried out on all the patients, by magnetic resonance and MEG. A characteristic pattern is obtained for SLD in the form of irregular spike and polyspike-wave discharges in bilateral frontal channels. The dipoles were situated mainly in the left perisylvian areas. The study of specific language disorders using MEG enables us to identify the SLD included in a proposed classification as primary-type specific language disorder, cryptogenic-type specific language disorder and secondary-type type specific language disorder, like Landau-Kleffner syndrome.