Quantitative EEG in attention-deficit/hyperactivity disorder

Abstract

Quantitative EEG measurement of the scalp vertex theta/beta ratio (TBR) is marketed as a tool for use in the evaluation of patients who may have attention-deficit/hyperactivity disorder (ADHD). The American Academy of Neurology (AAN) recently assessed the literature about this tool. The assessment urged caution, considering that the TBR remains an investigational research tool at this time. This perspective comments further on that assessment and its rationale, and recommends a perspective for the clinician and payer. Neurol Clin Pract 2016;6:543-548 T he use of quantitative EEG (QEEG) continues to receive attention as a controversial diagnostic aid for attention-deficit/ hyperactivity disorder (ADHD). For the purposes of this perspective piece, attention-deficit disorder is included in the definition of ADHD. The QEEG generally considered in the United States is the theta/beta ratio (TBR). TBR is the ratio of the amount of theta activity divided by the amount of beta activity, where both are measured at the scalp vertex site Cz. The ears are linked to use as reference electrode sites for the measurements, so these measurements include the EEG activity from both the scalp vertex and the lower temporal regions. In many studies, the TBR measurement is a single channel EEG based on 1-3 minutes of EEG. TBR measurement is available in commercial equipment. Commercial units display results as low, moderate, or high TBR without giving specific numeric values or raw EEG displays. The norms are age-adjusted. assessment 1 found a relative lack of support for the use of TBR tests for the diagnosis of ADHD. The 3 conclusions from that assessment are as follows: • Clinicians should inform patients with suspected ADHD and their families that the combination of TBR and frontal EEG beta power should not replace a standard clinical evaluation. • There is a risk for substantial harm to patients misdiagnosed with ADHD, given the high false-positive diagnostic rate of TBR and frontal EEG beta power. • Clinicians should inform patients with suspected ADHD and their families that the TBR should be used neither to confirm an ADHD diagnosis nor to support further testing after a clinical evaluation, unless such diagnostic assessments take place within the limits of a research study. Although some studies showed that TBR has a relatively high sensitivity and specificity for ADHD, the published literature was inconclusive. For example, one large recent study 2 based TBR measurements on 60 seconds of EEG. The gold standard for ADHD was unusual or unclear because patients with the most ADHD symptoms constituted the "ADHD-negative" control group. All patients were children referred to a specialized center for assessment of ADHD. Those considered to have a primary diagnosis of an anxiety, anger, or another disorder along with ADHD as a secondary diagnosis were considered ADHD-negative for this study, a classification that seemed peculiar because otherwise these patients would have been considered ADHD-positive patients. The classification decision ultimately compromised the gold standard in the study. There was no comparison to other childhood psychiatric or neurologic disorders as controls, and there were no normal controls. The diagnoses for the study were established upon initial referral, not upon follow-up, and the eventual diagnosis was unknown. The cutoff for "abnormal" was set at 1.5 SDs above the mean for age, so that 15% of the normal population would be expected by chance alone to be falsely positive. The authors were involved with commercialization of this product, which could be viewed as a conflict of interest. It seems wise to wait for further studies from investigators who do not have a commercial conflict of interest, who could run a study with a better gold standard, and in which other disorders and normal controls could be assessed. Uncertainties abound. Increased theta is a well-known, nonspecific EEG finding common to a wide variety of conditions. Many pathologic conditions cause excess central theta, and even simple drowsiness does so. EEG is subject to normal variant rhythms that are well-known to have no pathologic implications, including benign temporal theta or its central analog the Ciga-nek rhythm. Temporal theta could show up in these Cz channels because the ear reference electrodes are active and will detect temporal rhythms. For all these reasons, increased central theta or TBR is a suspect sign on which to base a diagnosis of ADHD. Background about ADHD and the TBR Increased central theta in children with behavioral disorders was reported in the 1930s. 3 Studies in the 1960s and 1970s confirmed excess theta activity in some childhood behavioral disorders. 4 The push to use a TBR as a diagnostic test began more than 15 years ago. Initial studies 5 described good sensitivity, specificity, and reliability for TBR as a diagnostic tool.