Resumen:

En este artículo se hace una revisión de las investigaciones más relevantes, en lo que concierne a la valoración neuropsicológica y su relación con la neurocirugía psiquiátrica. Además se propone un protocolo de evaluación para aquellos pacientes que son candidatos a este tipo de intervención, ya que hasta el momento, en México no se han dado estándares objetivos en este aspecto.

En tal sentido, el neuropsicólogo que realice la valoración debe tener experiencia en la evaluación de pacientes con trastornos psiquiátricos, ya que es necesario el conocimiento de los modelos de procesamiento de información que caracterizan a cada uno de éstos, para lograr una evaluación bajo un marco conceptual y empírico que permita la interpretación adecuada de los resultados. Asimismo, debe tener conocimiento de las técnicas neuroquirúrgicas empleadas en cada caso y saber las posibles secuelas de cada una de ellas.

El objetivo de incorporar valoraciones neuropsicológicas, antes y después de la operación, es obtener información precisa de los procesos y funciones que conforman el sistema cognoscitivo de cada persona, y de los cambios que se podrían presentar con posterioridad al proceso quirúrgico.

Por otro lado, la necesidad de realizar este tipo de valoraciones obedece a dos razones: constatar el probable deterioro que podría causar la intervención quirúrgica, y evaluar la mejoría secundaria a la disminución de los síntomas clínicos.

Lo anterior se asocia con el hecho de que el efecto que se logra mediante la lesión quirúrgica y la mejoría clínica, tienen dos cursos temporales distintos: el primero tendrá un resultado conductual más evidente durante el primer año postoperatorio en tanto que, en etapas posteriores, la disminución de síntomas clínicos será más obvia, y por ende se reflejará en la ejecución neuropsicológica.

Otra posibilidad que hay que considerar en este tipo de casos, es que los sistemas cerebrales relacionados con la psicopatología y aquéllos que subyacen al funcionamiento ejecutivo y cognoscitivo están distribuidos en el cerebro de forma diferente, y por tanto son afectados de manera distinta con este tipo de tratamiento.

Desde hace más de una década, en el Instituto Nacional de Psiquiatría Ramón de la Fuente (INPRF), tenemos protocolos de exploración neuropsicológica que se basan en la vasta experiencia clínica que se tiene con trastornos psiquiátricos, así como en la investigación realizada en esta institución. Asimismo, la integración de los estudios se adhiere a los parámetros internacionales de aplicación y de interpretación de estos instrumentos.

Con estas pruebas se pueden distinguir entre las alteraciones propias de la enfermedad y aquéllas que resultan de la neurocirugía, lo que a su vez se considerará para establecer estrategias de reha bilitación en caso de que fuera necesario.

Esta batería está compuesta por pruebas como la Escala de Inteligencia para Adultos de Wechler (WAIS), el Programa Integrado de Exploración Neuropsicológica-Test de Barcelona (versión abreviada), la Figura Compleja de Rey (estandarización en población mexicana, Instituto Nacional de Psiquiatría), el Test de Aprendizaje Verbal España Complutense (TAVEC).

Por otra parte, se propone el empleo de paradigmas que eva lúan distintas funciones a cargo del sector frontal del encéfalo, como el Test de Categorización de Tarjetas de Wisconsin (WCST), la Prueba de Stroop y Trazado con Hitos (Trail Making B).

Además, de lo señalado con anterioridad, deben tenerse en cuenta los cambios de personalidad que podrían surgir, ya que se han documentado alteraciones en la personalidad asociadas con hipofrontalidad en pacientes sometidos a capsulotomía, mismas que podrían deberse a errores de juicio.

La información obtenida por medio de la evaluación neuropsicológica, proporcionará datos objetivos en la toma de decisiones para el manejo interdisciplinario de los pacientes can didatos a neurocirugía psiquiátrica.

Palabras clave: Neuropsicología; neurocirugía psiquiátrica; trastorno obsesivo-compulsivo (TOC); esquizofrenia

Abstract:

Neuropsychology, as a part of cognitive neurosciences should be incorporated to the process of evaluation of any patient considered to be needing psychiatric neurosurgery, in order to obtain objective information of the processes and functions that shape each one's cognitive system and of the changes that may take place after surgery.

To attain this objective, the neuropsychologist doing the evaluation should be experienced in assessing patients with psychiatric disorders, as it is necessary to have a deep knowledge not only of the clinical characteristics of these ailments but also of the information processing models that typify each entity. Thus, by making an evaluation within a conceptual and empirical frame, an adequate interpretation of the results may be attained. At the same time it is necessary to know the neurochirugical techniques being applied in each case and also to be aware of the possible side effects that may take place.

The need for this type of assessments is due to two reasons: to find the possible damage that surgery may cause and to consider the improvement that follows the decrease of clinical symptoms.

The previous two facts are associated to clinical improvement as both have different temporal courses. The first will produce a behavioural effect more evident during the first post operative year while at further stages, the second will be made more evident with the decrease of clinical symptoms, thus reflecting on the neuropsychological performance.

Another possibility to be considered in this type of cases is that the cerebral systems related with psychopathology as well as those underlying executive and cognitive performance will be distributed differently in the brain and, therefore, with this kind of treatment they will be affected in a different way, this makes it necessary to do not only previous but subsequent evaluations in order to asses accurately the changes in the cognitive processes.

Also, should there be found more severe neuropsychological alterations than those expected for a specific psychiatric disorder, there is a risk of increasing post operative changes because any adverse surgical effect may interact or be added to the cognitive failures that typify the illness and, thus, prognosis will be worsened.

Regarding the most relevant research on this field, Dougherty et al. report that 20% of their 44 patients with obsessive compulsive disorder (OCD) mentioned at least one adverse effect; of these patients 5% reported a loss of memory that was corrected after six to 12 months. Among the writings that include neuropsychological evaluation as such, it was found that Nyman's group in Sweden, proposes that, independently form the neurosurgical technique used in patients with OCD, the main objective of the operation is to counteract the lack of balance between the frontal sector and the sub cortical regions, as well as that of the basal nuclei and the limbic structures. Therefore, as a proposal, they explore the functions pertaining to the frontal region because they believe that following surgery there must be failures in this area. This belief is also based on a previous research in which they found that five from ten patients presented after surgery a larger number of preservative answers in the Wisconsin Card Sorting Test (WCST), a fact that points out a dysfunction in the encephalon's anterior sector. Nevertheless, they consider that this preservative pattern of responses in the WCST is not permanent; on the contrary, there is improvement after capsulotomy, as shown when the evaluation results are compared to other patients' evaluations, previous to capsulotomy.

In another study they reported different failures depending of the surgical strategy being used; thus with frontal ventromedial lesion no alterations were found although when the ventral striated was involved, there were differences as to the number of categories and the conceptual level in WCST. Besides, the group with the worst ranging was the one with large lesions at dorsal level which gave place to visual spatial perception alterations, as well as to psychomotor slowness in a sequence task, and to intrusions in an associated learning task. This finding was expected because the extent of the regions affected by the lesion corresponds to the alterations observed.

No differences were reported in another research, as to the WAIS ratings or the Memory Scale of Wechsler, neither before nor after the operation. Nevertheless, the WCST showed some differences in regard to the categories established in respect to the control group, which were interpreted as a lack of abstract reasoning and cognitive flexibility.

In schizophrenic patients submitted to leucotomy because of their aggressive behaviour and lack of impulse control, follow up, while comparing their cognitive performance to that of other schizophrenic subjects who had not been operated, showed that there were negative effects on different cognitive aspects, although these, as part of the dysfunction expected for schizophrenia, were not caused by surgery.

Up to this moment, in Mexico there is not an evaluation protocol for patients needing psychiatric neurosurgery , and therefore, solid and objective standards should be established for this purpose.

For more than a decade, the Instituto Nacional de Psiquiatría Ramón de la Fuente (INPRF), has used neuropsychologic exploration protocols which are based not only on a wide clinical experience in the field of psychiatric disorders but also on the research carried out by our institution. Besides, integration of neuropsychological studies is based on international parameters designed to apply and interpret these instruments.

As well, with the same tests it is possible to distinguish between the alterations pertaining to illness and those resulting from neurosurgery. This, in turn will be considered for establishing, if required, reasoned rehabilitation techniques.

This battery is composed by the following tests: Wechsler Adult Intelligence Scale (WAIS), Integrated Program for Neuropsychological Exploration Test of Barcelona (Short Version), Rey's Complex Figure (Standarization for Mexican Population, Instituto Nacional de Psiquiatría), and Verbal Learning Test Spain Complutense (TAVEC).

This battery must be applied before the procedure, and follow up should be made for a period of between three, six to eight months, continuing with this evaluation protocol for at least three years. Nevertheless, flexibility may be allowed in case there should be complaints from the patient that justify making an evaluation before the given time.

On the other hand, considering the position and vulnerable condition in this type of surgical procedures paradigms that evaluate different functions of the frontal sector are proposed in order to obtain specific information of their functioning before and after intervention. We propose to use the Wisconsing Card Sorting Test (WCST), the Stroop Test and the Trail Making B.

In addition to the previous statements, the personality changes that may appear ought to be considered, because some personality alterations associated with hypo-frontality have been reported in patients submitted to capsulotomty, although such alterations may be due to judgement errors that are typical of cognitive damage.

Finally, we consider that within the selection and interdisci-plinary handling process for patients who may need psychiatric neurosurgery, information obtained from neuropsychological evaluation is necessary. Besides, it will allow the neuropsychologist, as part of the team in charge of these patients, not only to make realistic and objective suggestions regarding the therapeutic strate-gies to be used in each particular case, but also, to advise their relatives.

Key words: Neuropsychology; psychiatric neurosurgery; obsessive-compulsive disorder (OCD); schizophrenia