Funcionamiento neuropsicológico de adolescentes con trastorno bipolar / Neuropsychological functioning of adolescents with bipolar disorder

ABSTRACT

Persistent neuropsychological deficits have been reported in adult bipolar affective disorder, and impairments in executive functions, attention, verbal learning and memory, are postulated as neurocognitive endophenotypes. However, there is a lack of information about the neuropsychological functioning in Pediatric Bipolar Disorder (PBD). Hence, it is important to study this pediatric disorder because it could help, in first place, to clarify if children and adolescents with this disorder have neurocognitive impairments and secondly to analyze if the neuropsychological impairments in PBD are alike to those reported in adults. Neuropsychological characterization of PBD has been complicated because it has a 60%-90% comorbidity with Attention Deficit Hyperactivity Disorder (ADHD). Several studies have reported ADHD neuropsychological impairment in executive functions, sustained attention and working memory. Meanwhile, few studies in PBD have reported impairments in vigilance, working memory, interference control, speed processing, abstract problem solving and verbal learning. Yet, it is unknown if these deficiencies are distinct to the ones reported in ADHD or if they are a more severe manifestation of the same deficits. The objective of the present study was to assess the neuropsychological functioning of PBD by means of a battery of tests to analyze the capacities of complex problem solving, abstract reasoning and planning. We seeked if PBD presents other neuropsychological impairments beyond executive functions, verbal learning and memory, and attention that have been reported in adults with this disorder. Two groups were assessed, the first one included fourteen adolescent patients with PBD in euthimic phase, the other group consisted of eleven asyntomatic adolescents selected by means of absence of bipolar, affective, psychotic or neurodevelopmental disorders. Each participant was evaluated by certified neuropsychologists during three sessions of one hour each. As study variables we considered the general capacity for complex problem solving measured by subtest of the Intelligence Scales of Wechsler (WAIS or WISC-R) that were administered and qualified according to Lezak's proposals. We also assessed abstract reasoning, cognitive flexibility and planning measured by the Wisconsin Card Sorting Test (WCST) and Tower of London Drexel University (TOL DX). Results were analized with SPSS 11 program using U Mann-Whitney test with statistic significance at p <0.05 and <0.01. The results obtained, showed that adolescents with PBD had impairments in neuropsychological functioning. Some of the deficits are alike the impairments reported in adults with bipolar disorder, specially in tasks that involve executive funcioning like working memory and planning. Besides, we detected impairments in other neuropsychological measures that are associated with complex problem solving capacities that no other studies have reported, suggesting that PBD show neuropsychological impairments that go beyond those reported in adult patients. Capacities for complex problem solving were related to diminished scores for Wechsler's subtests of information, vocabulary, similarities, comprehension, picture completion, block designs and digit symbol. These subtests are associated with language abilities, concept formation, verbal reasoning, visual reasoning and speed of information processing. Although in our study adolecents with PBD scored within the normal range on Intellectual Quotient (IQ) full, verbal and executive scales, analysis showed statistical differences when compared to control group, suggesting a potentially more insidious impact of the early onset of the disorder on overall cognitive functioning. This impact can directly affect through disease evolves, or indirectly disrupting academic functioning. PBD group also differed from control group on variables that measured executive functions like planning and working memory as could be seen in Digit Span Wechsler's subtests and TOL 's total move, total rule violation and total execution time variables. Explanation of deficits could involve problems with speed processing, given the lower scores obtained on Wechsler's digit-symbol substitution subtest; or with executive deficits, such as organization and problem solving ruled out by working memory and language reasoning. Whatever the explanation could be, our data contributes to the possibility of a continuity of domains of neuropsychological impairment in people with early and later onset of bipolar disorder, although direct comparison of such groups is necessary in future studies. As such, these neuropsychological findings also could provide support for the validity of the differential diagnosis in children and adolescents with bipolar disorder. The neuropsychological impairments found in our research are consistent with the behavioral dyscontrol, poor frustration tolerance and impulsive aggression that are characteristic of PBD. It is proposed that the ability to regulate attention has implications for emotional regulation, meanwhile verbal reasoning deficits may reflect difficulties with effortful semantic processing, and impairments in executive functions such as working memory and planning, contribute to self-control and completion of goal-directed behavior. Together, deficits in these domains may impair the ability of PBD to attend to cues in the environment that assist the regulation of emotion and arousal, and to limit the ability for identifying and implementing novel and prosocial options for behavior by processing efficiently cues that are presented and ignore emotionally salient or distracting stimuly. It is important to point out that not all capacities for complex problem solving were impaired in PBD. There were no differences in Wechsler's subtests of object assembly, picture arrangement or arithmetic, neither differences were observed in TOL's variables of total correct, total time violation, total problem-solving or none of WCST variables. These findings can be associated with preserved capacities for set shifting, abstract reasoning, interference control, arithmetic reasoning, sequencing thinking, interpretation of socio-emotional clues and visuo-spatial planning. However, more work is needed to elucidate the meaning of this preserved capacities and how they interact with the impairments already discussed. In this sense, it is possible to speculate that although the impairments already described can influence on academic functioning, the preserved capacities might exert an important role in the regulation of adaptive behavior. As a conclusion, our data indicate neuropsychological deficits in youth with PBD in domains of executive functioning and capacities for general problem solving. These findings add to a growing body of work documenting the presence of neurocognitive underpinnings of bipolar disorder in adolescents. Data suggests that measures of verbal reasoning, visual reasoning, speed processing, working memory and planning might be explored further in future functional neuroimaging studies of PBD.

RESUMEN

Los estudios neuropsicológicos del trastorno bipolar en adultos han señalado alteraciones en las funciones ejecutivas, mnésicas y atencionales como endofenotipos neurocognitivos del trastorno. Sin embargo, se conoce poco sobre la caracterización neuropsicológica del Trastorno Bipolar Pediátrico (TBPP), misma que ha sido complicada dado que existe una comorbilidad del 60%-90% con el Trastorno por Déficit de Atención con Hiperactividad (TDAH). Así, desde la perspectiva neuropsicológica, el TBPP ha sido poco estudiado. Existen algunas investigaciones que no reportan alteraciones neurocognitivas, y otras reportan deficiencias en tareas de vigilancia, memoria de trabajo, control de interferencia, velocidad de procesamiento, solución de problemas abstractos y aprendizaje verbal. Sin embargo, aún se desconoce si estas deficiencias son distintas a las observadas en el TDAH, o si son formas más severas de las mismas alteraciones del TDAH. Por lo tanto, el objetivo del presente estudio fue evaluar el funcionamiento neuropsicológico del TBPP por medio de una batería de pruebas integrada para analizar las capacidades en la solución de problemas complejos, razonamiento abstracto y habilidades de planeación. Esto con la finalidad de valorar si el TBPP cursa con otras alteraciones neuropsicológicas, más allá de la esfera de la atención, memoria y del funcionamiento ejecutivo, como se han descrito hasta el momento en adultos con trastorno bipolar. Así, se comparó el funcionamiento neurocognitivo en un grupo de 14 pacientes adolescentes con diagnóstico de TBPP en fase de eutímia y un grupo control de 11 adolescentes asintomáticos. Además, se consideraron como variables del estudio la capacidad general para solucionar problemas, medida por medio de las subpruebas de las Escalas de Inteligencia de Wechsler, así como las habilidades de razonamiento abstracto, flexibilidad cognoscitiva y planeación, medidos con el Test de Clasificación de Tarjetas de Wisconsin y la Torre de Londres Drexel University. Los resultados señalaron que los adolescentes con TBPP presentan alteraciones en el funcionamiento neuropsicológico. Algunas de las deficiencias encontradas son parecidas a las alteraciones reportadas en adultos, especialmente ante tareas que involucran funciones ejecutivas como la memoria de trabajo y la planeación. Además de esto, se detectaron alteraciones en otras mediciones neuropsicológicas que implican la capacidad para solucionar problemas complejos y que no han sido reportadas en estudios previos. Al evaluar la capacidad general para solucionar problemas, se encontraron alteraciones en las habilidades de lenguaje, formación de conceptos, razonamiento verbal, razonamiento visual práctico/ conceptual, análisis-síntesis visual y velocidad de procesamiento. También se observaron deficiencias en las funciones ejecutivas que involucran la planeación y la memoria de trabajo. De tal manera, que nuestros datos ofrecen la posibilidad de plantear una continuidad en la alteración de las funciones ejecutivas en el trastorno bipolar tanto de inicio temprano como en el tardío. Estos hallazgos también pueden considerarse un apoyo para la validez del diagnóstico diferencial del trastorno bipolar en adolescentes. Como conclusión, podemos señalar que nuestros resultados son consistentes con la bibliografía en general al indicar que existen deficiencias neuropsicológicas en adolescentes con TBPP, al tiempo que se mencionan otras alteraciones no descritas con anterioridad. Estas deficiencias involucran el funcionamiento ejecutivo y otros dominios cognitivos que influyen sobre la capacidad general para solucionar problemas. Además, se sugiere que las mediciones que involucran el razonamiento verbal, razonamiento visual, velocidad de procesamiento, memoria de trabajo y planeación podrían examinarse con mayor detenimiento en futuros estudios de neuroimagen funcional en el TBPP.