Neurobiological measures to classify ADHD: a critical appraisal

Excerpt

"We need to get rid of the uncertainty of psychiatric diagnoses. We should instead use a biological test, based on—for instance—brain activation or blood levels. Using such tests, we will be able to objectively determine whether someone suffers from attention-deficit/hyperactivity disorder (ADHD) or from psychosis. That way, the problem of over- and under-diagnosing in psychiatry will be solved. In addition, we will know for certain whether treatment—medication, therapies, or a diet—will be effective" (translation of the first paragraph of the article ‘The ADHD brain can not be known’ [Het ADHD brein laat zich niet kennen] written by S. Voormolen and published in a leading Dutch newspaper NRC [Nieuwe Rotterdamse Courant], 30 November 2014). The article discusses the clinical implications of the recent study by Mazaheri et al. [13], who examined oscillatory changes in theta, alpha, and beta EEG bands in 57 adolescents (34 with ADHD) performing a cued flanker task. Adolescents with ADHD showed, on average, weaker functional connectivity between frontal theta and posterior alpha, suggesting a top-down impairment of control. In addition, there were some specific differences in underlying neuronal activation patterns between children with ADHD-predominantly inattentive (ADHD-PI) and children with ADHD-combined (ADHD-C) subtypes, with the ADHD-PI children showing less post-cue alpha suppression at the electrode contralateral to the cued response hand (suggesting diminished processing of the cue in the visual cortex) and the ADHD-C children showing less beta suppression at the electrode contralateral to the cued response hand (suggesting poor motor planning). Mazaheri and colleagues concluded that “task-induced changes in EEG oscillations provide an objective measure, which in conjunction with other sources of information might help distinguish between ADHD subtypes and therefore aid in diagnoses and evaluation of treatment.” At first glance, these results, although interesting, are not particularly novel. There have been earlier reports of differences in neuropsychological or brain imaging findings between ADHD and control subjects, or between subjects with different ADHD subtypes (for example, [14, 18, 19]). Why then, did this specific article prompt the publication of a provocative article in a leading national newspaper? Perhaps it was the first sentence of the abstract that spurred popular interest—“a neurobiological-based classification of ADHD subtypes has thus far remained elusive.” Mazaheri and colleagues apparently think that it would be better to classify ADHD on the basis of neurobiological markers instead of the current methods based on informant report and clinical evaluation of behavior. Indeed, many investigators have expressed the hope that biological markers will be included as diagnostic criteria in the DSM [11, 15]. …