Potenciales relacionados con eventos y comorbilidad en un grupo de adolescentes con trastorno por déficit de atención con hiperactividad

SUMMARYAttention deficit hyperactivity disorder (ADHD) is a neuro-developmental disorder clinically characterized by three core symptoms:deficits in attentional processes, failure in inhibitory control —usuallyexpressed through behavioral and cognitive impulsiveness—, andmotor and verbal restlessness.Deficit in attentional resources is the main alteration in patientswith this disorder. Attention can be considered as a neurocognitivestate of neural preparation that precedes both perception and action.Attention focalizes consciousness in order to filter the constant flux ofsensorial information, solve competence between stimuli for parallelprocessing and recruit and activate cerebral regions necessary toaccomplish appropriate responses.Event-related potentials (ERPs) are a technique that has provenuseful in the gathering of valuable information in the study of ADHD.One of the most studied ERPs is the P300 component. The most robustfinding in the P300 research in ADHD is a decrease in the amplitudeof the component in patients when compared to normal controls. Thisfinding is usually interpreted as an evidence for a deficit in attention.ADHD usually presents commorbidity with several disorders;research shows that up to 87% of the children with ADHD presentcommorbidity with another disorder, up to 60% has either a behavioralor affective disorder commorbid with ADHD. Due to the wide range ofdisorders that are usually associated with this entity, it is useful in theresearch of commorbidity to use dimensional diagnostics, that is, apatient with ADHD may have commorbidity with an externalizeddisorder (EXT) (i.e. oppositionist defiant disorder); an internalized (INT)disorder (i.e. anxiety or affective disorder); or both an externalizedand an internalized disorder (MIX). Commorbidity may have importantimplications in the electrophysiology of ADHD since no homogeneousresults have been evident in the scarce research on the subject.Taking into account these considerations, the followingexperiment was designed in order to answer the question: Patientswith the same main diagnostic, ADHD, but different commorbidities(INT and MIX) show different psychophysiological patterns ofactivation, as measured by ERPs to a continuous performance task? Sixteen patients diagnosed with ADHD by a specialist wererecruited. Diagnosis was corroborated by a semi-structured interview,K-SADS-PL-MX, eight of them with an externalized comorbid (EXT)disorder, and eight of them with at least two comorbid disorders,one externalized an one internalized (MIX). A control group (CON)of eight normal subjects with no psychiatric diagnostic and matchedby sex was also recruited. All subjects were between 13-16 years oldwith no history of Central Nervous System damage and normal IQ inthe Weschler Intelligence Scale for Children. Brain electrical activitywas recorded in the 19 derivations of the 10-20 international systemwhile subjects executed a continuous performance task (CPT). Comparisons of behavioral data between groups showed somesignificant differences. A one-way ANOVA found differences betweengroups in the mean reaction time to the first part of the CPT and inthe number of false positives in the second part.Electrophysiological data was analyzed with a non-parametricalmultivariate test of permutations. When comparing responses to thefrequent stimulus with responses to the infrequent, statistically significantdifferences were found in every subject; such differences share thetopography and latency characteristics of the P3b component. Whencomparing the amplitude of this component between the groups, onlytwo statistically significant differences were found.First, the EXT group presented a greater amplitude of thecomponent elicited by the first part of the task in a latency of 425 to445 msec in the parietal region of the medial line than the CONgroup. Second, also in response to the first part of the task, theamplitude of the CON group was bigger than that of the MIX groupin a latency between 355 and 420 msec in the left temporal anteriorregion. No other comparison yielded significant results.When comparing between groups, mean reaction time to thefirst part of the task was the only behavioral variable that adequatelydistinguished control and patients. Even though controls executedsignificantly faster, they maintained the same efficacy as no differenceswere found in the number of errors or correct responses. This resultis not surprising due to the fact that long reaction times usually denoteinattention and so the fact that both groups of patients execute slowerthan the controls may be interpreted as a sign that, in spite of havingdifferent commorbidities, inattention is still a common problem inevery patient of the sample.On the second part of the task, only the number of false positivesshowed statistically significant differences. However, in a posterior