Aportes del electroencefalograma convencional y el análisis de frecuencias para el estudio del trastorno por déficit de atención. Primera parte

• Autores: Josefina Ricardo Garcell
• Localización: Salud mental, ISSN 0185-3325, Vol. 27, Nº. 1, 2004, págs. 22-27
• Idioma: español
• Enlaces
  • Texto completo (pdf)
• Dialnet Métricas: 5 Citas
• Resumen
  • español

    El Trastorno por Déficit de Atención (TDA) es un trastorno crónico del desarrollo que se caracteriza fundamentalmente por una disminución en el espectro de la atención; por dificultades en el control inhibitorio que se expresa a través de la impulsividad conductual y cognoscitiva; y por una inquietud motora y verbal. Estas características deben aparecer antes de los siete años de vida, según lo establece la taxonomía internacional, y ser inapropiadas para la edad o el nivel de desarrollo del paciente. Existen pocos procedimientos de evaluación objetivos disponibles por lo que, teniendo en cuenta que el TDA se considera como resultado de una disfunción del Sistema Nervioso Central (SNC) y que el electroencefalograma (EEG) suministra una medida directa del funcionamiento cerebral, éste parece ser una herramienta apropiada para evaluar este trastorno.

    La contribución del EEG tradicional al estudio del TDA ha tenido interpretaciones variables pero predominan los autores que refieren la presencia de anormalidades frecuentes en el EEG de estos pacientes. Auque la anormalidad más común consiste en un incremento de la actividad lenta, también se ha señalado que tienen un porcentaje significativamente mayor de actividad epileptiforme que los niños normales, y que la misma es más evidente durante la hiperventilación y la fotoestimulación. El análisis cuantitativo del EEG, particularmente en el dominio de las frecuencias, abrió nuevas posibilidades para el estudio de los pacientes con TDA.

    Entre las principales anormalidades encontradas con las medidas espectrales de banda ancha (MEBAs) se encuentran: 1. aumentos de las potencias theta absoluta y relativa, 2. aumentos de los cocientes theta/alfa y theta/beta, 3. disminución difusa en las frecuencias medias de las bandas alfa y beta, 4. anormalidades interhemisféricas (asimetría de potencia y disminución de la coherencia entre las regiones parietales y entre las temporales posteriores, aumento marcado de la coherencia entre las regiones frontales y las centrales), y 5. intrahemisféricas (asimetrías de potencia entre las regiones frontal/temporal y frontal/occipital, aumento de la coherencia fronto-temporal y disminución de la coherencia fronto-occipital). Algunos autores han interpretado estas alteraciones como un retraso en la maduración de la actividad eléctrica cerebral; a su vez, OTROS las han interpretado como una desviación del desarrollo de la misma.

    El primero se refiere a la presencia de hallazgos electroencefalográficos anormales, que podrían ser normales en un niño de menor edad cronológica, mientras que en la desviación del desarrollo existen patrones electroencefalográficos anormales, que no serían normales a ninguna edad. Estas variantes pueden verse en pacientes con diferentes diagnósticos clínicos, por lo que actualmente se enfatiza la presencia de subgrupos electrofisiológicos en este tipo de pacientes, independientemente de su diagnóstico clínico. En general, se ha señalado que son frecuentes las alteraciones de las MEBAs en pacientes con TDA, y llegan a alcanzar valores tan altos como entre 85-90% en diferentes muestras de pacientes. Se ha sugerido la utilidad de las MEBAs para el tratamiento mediante neurorretroalimentación y para evaluar la respuesta al tratamiento con estimulantes.

    También se ha enfatizado la importancia de realizar investigaciones sobre la relación existente entre las MEBAs y variables de las pruebas neuropsicológicas que se aplican frecuentemente en este tipo de pacientes. Asimismo, resulta de gran interés estudiar cuáles son los verdaderos generadores de la actividad eléctrica cerebral anormal en estos pacientes. Finalmente, aun cuando hay quienes consideran que el análisis de frecuencias del EEG no es recomendable como procedimiento diagnóstico ni para tomar decisiones terapéuticas en pacientes con TDA, hay quienes estiman que esta técnica ha alcanzado su madurez y demostrado su utilidad en diferentes afecciones psiquiátricas.

    Además, si se consideran los resultados obtenidos con las MEBAs en el TDA, que el EEG brinda información sobre el funcionamiento cerebral, que es una técnica no invasiva y mucho más económica que los estudios de imágenes cerebrales, puede valorarse como una buena opción para evaluar a los pacientes con TDA y su futura introducción en la práctica clínica. Por tanto, todo esfuerzo que se haga en esta dirección se debe evaluar constructivamente y no se debe rechazar por mal uso, desconocimiento, rigidez o impaciencia profesional.

  • English

    Attention deficit disorder (ADD) is a chronic developmental disorder, characterized mainly by: decrease in attention, cognitive and behavioral impulsiveness due to a weak inhibitory control, and motor and verbal restlessness. According to the international taxonomy, all these symptoms must be evident by the age of 7, and inappropriate for the age or level of development of the patient. There are very few objective evaluation methods available, and if one bears in mind that ADD is considered as the result of a dysfunction in the Central Nervous System (CNS), and that the electroencephalogram (EEG) is a direct measure of brain performance, this seems like an adequate tool to evaluate this disorder. The contribution of traditional EEG to the research on ADD is controversial but most of the authors report the presence of frequent abnormal activity in the EEG of these patients. The most common abnormality is an increase in the slow activity but it has also been reported that they have a significantly higher percentage of epileptic activity than normal kids, which it is more evident during hyperventilation and photostimulation. Quantitative analysis of EEG, particularly in the frequency domain, opened new possibilities for the study of ADD. Among the abnormalities found with broad band spectral parameters (BBSP) the most frequent are: 1. increase in theta absolute power (AP) and relative power (RP), 2. increase in the theta/alpha and theta/beta coefficients, 3. non-specific decrease in the midfrequencies of the alpha and beta bands, 4. inter hemispheric abnormalities (power asymmetry and a reduction in the parietal– posterior temporal coherence, increase in the frontal–central regions coherence), 5. intra hemispheric (power asymmetry between the frontal-temporal and frontal–occipital regions, increase in the frontal–temporal coherence and reduction in the frontal–occipital coherence). These findings have been explained by some as a maturational lag in the brain electrical activity development, while others believe them to be a deviation of it. This maturational lag means that the electroencephalographic abnormalities reported would be normal in a younger child, while a deviation of development would mean the presence of abnormal electrical patterns that would not be normal under any circumstance at any age. A maturational lag may eventually disappear as the patient grows old, while a deviation in development is commonly believed to be a dysfunction of the CNS. Most BBSP studies in ADD have been done with the patient’s eyes closed, resting; nevertheless, open-eyes studies have come up with very similar results. Abnormalities in the BBSP of different samples of ADD patients as those pointed out have been found in up to 85–90%. On the other hand, a great disadvantage of most EEG studies is the assumption of clinically homogeneous groups, but there is plenty of evidence suggesting that ADD may represent a heterogeneous population, with different underlying electrophysiological abnormalities. A recent study in Mexico City found different patterns in the BBSP results of 154 ADD patients: theta (20%) or alpha (22%) as the most significant activity, specially in the anterior and medial regions, increase in beta activity as the only abnormality (2%), increase in the slow activity specially delta (6%), non–specific abnormalities (25%), a pattern suggesting a maturational lag in the brain electrical activity development (10%) and without abnormalities in these measures (15%). The percentage of patients with normal EEG may account for the fact that some clinicians underestimate the value of these measures for the study of ADD. It is noteworthy that there is plenty of evidence that the patterns of maturational lag and deviation of brain electrical activity development may be found in patients with different clinical diagnostic. In the treatment issue, BBSP have been used mainly in two fields: neurofeedback and pharmacological treatment. There has been plenty of research about the former, but most of it is easily criticized on its methodological grounds. Nevertheless, in the last few years, some publications have tried to overcome this issue, and to pinpoint the capability of this technique to lessen slow activity in the EEG. Changes in BBSP after 6–14 months of treatment with stimulants (metilphenidate and dexamphetamine) are not consistent in the literature. There is evidence that patients with an increase in alpha and beta activity are more likely to show a reduction of behavioral symptoms. The probability of a positive outcome lessens and the probability of a negative outcome increases when patients have an excess of theta activity. Nevertheless, there is also evidence that those patients with a good outcome to treatment with metilphenidate have an evident excess of theta activity in relation to those with a poor outcome, while in using dexamphetamine it is noteworthy that the more evident a profile of maturational lag of EEG, the better the outcome. For these authors stimulants tend to “normalize” EEG (particularly theta and beta bands), especially in those patients with a profile of increased theta band activity and decreased beta band activity. ADD is a disorder more frequent in males, and that may be the reason for their greater percentage over females in almost every sample. However, it has been found that ADD girls (either combined or predominantly inattentive subtypes) have the same pattern of increased theta and decreased beta activity seen in boys, but they are not as heterogeneous as them. The analysis of changes in EEG in relation with age suggests that there are two independent components that constitute the actual diagnostic of the DSM-IV and that both are correctly measured using electrophysiological variables: 1. a hyperactive/impulsive component that appears to be accounted for by a maturational lag in development of CNS, because it tends to normalize itself with an increase in age, and 2. a inattentive component that does not seem to normalize with the increase in age and that is associated with a deviation of development of the CNS. Most of the research available defines maturational lag or deviation in the brain electrical activity development comparing ADD patients with normal controls, but not in the age changes that occur in a population of patients with this disorder. Because of this, it has been said, by comparing groups of children, adolescents and adults with ADD, that the three groups have and increase in the theta band and that the decrease in the beta activity evident in relation to controls is smaller as age increases. Because the hyperactivity component also decreases as age increases but impulsivity does not, the former has been associated with the beta activity, while the latter with the theta activity. More research is needed before anything complete can be said about comorbility and how it may alter or not the results of the EEG of patients with ADD. However, everything seems to point that at least when ADD is found with a learning disorder or an oppositional defiant disorder, there are some electrophysiological findings of ADD not accounted for by the comorbid disorder. It has also been suggested that the absolute power of the EEG may be affected by a Global Scale Factor (GSF), which contributes to 42% of the total variance of age corrected data, but that is rarely subtracted from the AP. This becomes particularly important if it is noted that some patients with ADD show significant decreases in the slow activity, but, as is noted by some, when the subtraction of GSF is done, an abnormal excess of slow activity not seen before becomes evident. Another aspect not usually taken into account is the existing association between spectral parameters of EEG and frequently used neuropsychological variables. There is some reference to research already started in our country in this line. Yet another poorly developed side is the very few works analyzing the abnormal sources of brain electrical activity in ADD patients. They represent a necessary alternative for the knowledge of the real generators of abnormal brain electrical activity in these patients. Finally, even when there are those who consider that frequency analysis of EEG is not recommended as a diagnostic procedure or as a tool in the process of taking therapeutic decisions in patients with ADD, there are those who think that this should not be taken as a definitive opinion, because EEG frequency analysis has reached a level in which its utility in several different psychiatric disorders has been proven. EEG offers information about brain functioning, is a non–invasive technique and less expensive than any brain image technique, and the results of BBSP in ADD confirm that any effort in this direction should be fairly evaluated and not easily discarded because of misuse, poor knowledge, stiffness, or lack of patience.