Disociaciones en el rendimiento práxico en pacientes con demencia tipo Alzheimer: imitación de gestos transitivos, intransitivos y no familiares

Abstract

En el contexto de evaluación de praxias, los gestos pueden clasificarse en transitivos, intransitivos y no familiares. Si bien ha sido reportada la disociación entre los distintos tipos de gestos, es usual que en la evaluación de praxias o en el análisis del desempeño de los pacientes no se consideren por separado estas tres categorías de gestos, o se varíe la definición de estas categorías.El objetivo de este estudio es evaluar si en un mismo grupo de pacientes con demencia tipo Alzheimer se encuentran disociaciones entre gestos transitivos, intransitivos y no familiares, previamente descriptas en el rendimiento práxico de pacientes con lesiones focales (González Rothi, Mack, Verfaellie, Brown & Heilman, 1988; Negri et al., 2007).Se evaluó a 50 pacientes con diagnóstico de demencia tipo Alzheimer probable en imitación de praxias (gestos transitivos, gestos intransitivos y gestos no familiares) y uso de objetos. Los estímulos fueron tomados de la batería cognitiva de evaluación de praxias (Politis, 2003). Los gestos eran inicialmente realizados por el examinador, quien mantenía su ejecución durante la imitación del paciente.El grupo con diagnóstico de demencia tipo Alzheimer rindió significativamente peor que los controles sanos. En el grupo de pacientes las cuatro pruebas de praxias correlacionaron entre si. Sin embargo, se hallaron disociaciones en el rendimiento individual de cada paciente en esas mismas pruebas. La disociación entre gestos transitivos, intransitivos y no familiares apoya la posibilidad de que estos diferentes tipos de gestos involucren sistemas de procesamiento distintos.

Apraxia is classically defined as a difficulty or inability to imitate gestures, produce pantomimes of tool's use, or make gestures to verbal command. In apraxia assessment, gestures can be classified in transitives, intransitives, and non-familiars. The movements are classified according to the purpose of the motor act: if involves manipulation of an object, if serves to communicate ideas or feelings, or if it lack of any practical or symbolical value. Whilst the selective impairment for the processing of transitive gestures was widely reported, a deficit restricted to intransitive gestures was reported only exceptionally. Although it has been reported dissociation between different types of gestures, is usual in apraxia assessment that these three categories of gestures don't be considered separately or that varies the definition of these categories. The aim of this study was verify the presence of dissociations between transitives, intransitives, and non-familiars gestures in a same group of patients with Alzheimer-type dementia, that was previously described in the praxias performance of patients with focal lesions (González Rothi, Mack, Verfaellie, Brown, & Heilman, 1988; Negri et al., 2007). It was assessed imitation of transitives, intransitives and non-familiar gestures, and the use of objects, in 50 patients of the Neurology Department of Eva Perón Hospital (Buenos Aires -Argentina) diagnosed with probable Alzheimer-type dementia, under the diagnostic criteria of NINCDS - ADRDA. The Alzheimer-type dementia group performed the tasks significantly worse than healthy controls. 72% showed deficit in the per formance of at least one of the praxis battery tests. In Alzheimer-type dementia group, each praxis subtest are significantly and positively correlated with the others. However, there were dissociations in the performances at the single-case level analysis. One patient (Case 3) showed a selective deficit in imitation of intransitives gestures, while retaining the imitation of transitives gestures and non-familiar gestures; five patients (Cases 16, 23, 31, 45, and 46) showed an exclusively impairment in the imitation of transitives gestures while retaining the imitation of intransitives gestures and non-familiar gestures; and five patients (Cases 2, 6, 12, 14, and 29) showed a deficit only in the imitation of non-familiar gestures, while retaining the imitation of transitives and intransitives gestures. The dissociation between transitives, intransitives, and non-familiar gestures supports the possibility that these different types of gestures implicate different processing systems. The presence of double dissociations points out that the processes underlying each task, at least, are partially independent, and can be affected in a differentiated way. The finding of alterations in the three types of gestures questions the hypothesis that ideomotor apraxia is a disorder in the representations underlying transitives gestures (Buxbaum et al., 2005). The double dissociation found in theimitation of familiar gestures and non-familiar gestures provides new evidence for a non-lexical path, exclusive for imitating non-familiar gestures (González Rothi, Ochipa, & Heilman, 1991) and contradicts the model of ideomotor apraxia that propose a common substrate for lexical path and non-lexical pathway, linked to body schema (Buxbaum, Giovannetti, & Libon, 2000). The results of this work show the value of the study of multiple cases for the validation of cognitive models in patients with brain injuries. It is transcendent the systematic exploration and analysis of the different types of gestures in apraxic patients, in theoretical terms and with a view to developing clinical advantages in identifying and potentially rehabilitate apraxia.