Abstract

CASTANEDA FRANCO, Marisol; TIRADO DURAN, Elsa; FERIA, Miriam  and  PALACIOS CRUZ, Lino. Neuropsychological functioning of adolescents with bipolar disorder. Salud Ment [online]. 2009, vol.32, n.4, pp.279-285. ISSN 0185-3325.

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.

Keywords : Bipolar disorder; adolescence; neuropsychology; cognition.