Attention-deficit/hyperactivity disorder: cognitive evoked potential (P300) amplitude predicts treatment response to atomoxetine

Treatment biomarkers for ADHD: Taking stock and moving forward

The development of treatment biomarkers for psychiatric disorders has been challenging, particularly for heterogeneous neurodevelopmental conditions such as attention-deficit/hyperactivity disorder (ADHD). Promising findings are also rarely translated into clinical practice, especially with regard to treatment decisions and development of novel treatments. Despite this slow progress, the available neuroimaging, electrophysiological (EEG) and genetic literature provides a solid foundation for biomarker discovery. This article gives an updated review of promising treatment biomarkers for ADHD which may enhance personalized medicine and novel treatment development. The available literature points to promising pre-treatment profiles predicting efficacy of various pharmacological and non-pharmacological treatments for ADHD. These candidate predictive biomarkers, particularly those based on low-cost and non-invasive EEG assessments, show promise for the future stratification of patients to specific treatments. Studies with repeated biomarker assessments further show that different treatments produce distinct changes in brain profiles, which track treatment-related clinical improvements. These candidate monitoring/response biomarkers may aid future monitoring of treatment effects and point to mechanistic targets for novel treatments, such as neurotherapies. Nevertheless, existing research does not support any immediate clinical applications of treatment biomarkers for ADHD. Key barriers are the paucity of replications and external validations, the use of small and homogeneous samples of predominantly White children, and practical limitations, including the cost and technical requirements of biomarker assessments and their unknown feasibility and acceptability for people with ADHD. We conclude with a discussion of future directions and methodological changes to promote clinical translation and enhance personalized treatment decisions for diverse groups of individuals with ADHD.

Altered Auditory P300 Performance in Parents with Attention Deficit Hyperactivity Disorder Offspring

Objective

Altered event-related potential (ERP) performances have been noted in attention deficit hyperactivity disorder (ADHD) patients and reflect neurocognitive dysfunction. Whether these ERP alterations and correlated dysfunctions exist in healthy parents with ADHD offspring is worth exploring.

Methods

Thirteen healthy parents with ADHD offspring and thirteen healthy controls matched for age, sex and years of education were recruited. The auditory oddball paradigm was used to evaluate the P300 wave complex of the ERP, and the Wechsler Adult Intelligence Scale-Revised, Wisconsin Card Sorting Test, and continuous performance test were used to measure neurocognitive performance.

Results

Healthy parents with ADHD offspring had significantly longer auditory P300 latency at Fz than control group. However, no significant differences were found in cognitive performance.

Conclusion

The presence of a subtle alteration in electro-neurophysiological activity without explicit neurocognitive dysfunction suggests potential candidate of biological marker for parents with ADHD offspring.

A Signature of Attention-Elicited Electrocortical Activity Distinguishes Response From Non-Response to the Non-Stimulant Atomoxetine in Children and Adolescents With ADHD

OBJECTIVE

Atomoxetine has several characteristics that make it an attractive alternative to stimulants for treating ADHD, but there are currently no tests identifying individuals for whom the medication should be a first-line option.

METHOD

Within the ADHD Controlled Trial Investigation Of a Non-stimulant (ACTION) study, we examined neuro-cortical activity in 52 youth with ADHD. Baseline event-related potentials (ERP) were compared between those who subsequently responded to 6 weeks of atomoxetine versus those who did not.

RESULTS

Responders were distinguished by significantly lower auditory oddball N2 amplitudes than both non-responders and typically developing controls, particularly in the right frontocentral region ( p = .002, Cohen's d = 1.1). Leave-one-out cross validation determined that N2 amplitude in this region was able to accurately predict non-responders with a specificity of 80.8%. There were no P3 differences between responders and non-responders.

CONCLUSION

The N2 amplitude is a biomarker that may have utility in predicting response to atomoxetine for youth with ADHD.

Personalized Medicine: Review and Perspectives of Promising Baseline EEG Biomarkers in Major Depressive Disorder and Attention Deficit Hyperactivity Disorder

Personalized medicine in psychiatry is in need of biomarkers that resemble central nervous system function at the level of neuronal activity. Electroencephalography (EEG) during sleep or resting-state conditions and event-related potentials (ERPs) have not only been used to discriminate patients from healthy subjects, but also for the prediction of treatment outcome in various psychiatric diseases, yielding information about tailored therapy approaches for an individual. This review focuses on baseline EEG markers for two psychiatric conditions, namely major depressive disorder and attention deficit hyperactivity disorder. It covers potential biomarkers from EEG sleep research and vigilance regulation, paroxysmal EEG patterns and epileptiform discharges, quantitative EEG features within the EEG main frequency bands, connectivity markers and ERP components that might help to identify favourable treatment outcome. Further, the various markers are discussed in the context of their potential clinical value and as research domain criteria, before giving an outline for future studies that are needed to pave the way to an electrophysiological biomarker-based personalized medicine.

Toward quality care in ADHD: defining the goals of treatment

OBJECTIVE

Therapeutic goals for chronic mental disorders like major depressive disorder (MDD) and schizophrenia have evolved in parallel with the growing medical knowledge about the course and treatment of these disorders. Although the knowledge base regarding the clinical course of ADHD, a chronic psychiatric disorder, has evolved beyond symptomatic improvement and short-term treatment response, long-term goals, such as functional remission, have not yet been clearly defined.

METHOD

A PubMed literature search was conducted to investigate the therapeutic goals of pharmacologic treatment referenced in the published literature from January 1998 through February 2010 using the following commonly used ADHD treatments as keywords: amphetamine, methylphenidate, atomoxetine, lisdexamfetamine, guanfacine, and clonidine. This search was then combined with an additional search that included the following outcome keywords: remission, relapse, remit, response, normal, normalization, recovery, and effectiveness.

RESULTS

Our search identified 102 publications. The majority (88.2% [90/102]) of these contained predefined criteria for treatment response. Predefined criteria for normalization and remission and/or relapse were presented in 4.9% (5/102), 12.7% (13/102), and 3.9% (4/102) of publications, respectively. There was a lack of consistency between the instruments used to measure outcomes as well as the criteria used to define treatment response, normalization, and remission as well as relapse.

CONCLUSION

The therapeutic goals in treating ADHD should address optimal treatment outcomes that go beyond modest reductions of ADHD symptoms to include syndromatic, symptomatic, and functional remission. Future work should focus on reliable and valid tools to measure these outcomes in the clinical trial setting.

Attention-deficit/hyperactivity disorder: neurophysiology, information processing, arousal and drug development

In this review, we draw on literature from both animal and human neurophysiological studies to consider the neurochemical mechanisms underlying attention-deficit/ hyperactivity disorder (ADHD). Psychophysiological and neuropsychological research is used to propose possible etiological endophenotypes of ADHD. These are conceptualized as patients with distinct cortical-arousal, information-processing or maturational abnormalities, or a combination thereof, and how the endophenotypes can be used to help drug development and optimize treatment and management. To illustrate, the paper focuses on neuro- and psychophysiological evidence that suggests cholinergic mechanisms may underlie specific information-processing abnormalities that occur in ADHD. The clinical implications for a cholinergic hypothesis of ADHD are considered, along with its possible implications for treatment and pharmacological development.

Differential effects of methylphenidate and atomoxetine on attentional processes in children with ADHD: an event-related potential study using the Attention Network Test

Methylphenidate (MPH) and atomoxetine (ATX) are effective medications in the treatment of attention deficit/hyperactivity disorder (ADHD). The aim of this study was to investigate differential effects of MPH and ATX on attentional functions at the performance and the neuronal level in children with ADHD. Using the Attention Network Test (ANT), differential effects of both medications on the noradrenergic alerting network and the dopaminergic executive attention network were considered. Nineteen children with ADHD performed the ANT three times while event-related potentials (ERPs) were recorded. The baseline testing was conducted without medication. In two medication blocks of 8 weeks each, medication was individually titrated for each child (cross-over design, balanced order). At the end of the medication blocks the testing was repeated. While both medications comparably reduced ADHD symptomatology, MPH had some advantages over ATX with regard to performance measures on the ANT and the underlying neuronal mechanisms. Compared with ATX, MPH led to a larger reduction in reaction time variability, which was accompanied by an MPH-related increase in the contingent negative variation (CNV) compared to the baseline testing. Contrary to our expectations, specific alerting network effects were not observed with ATX. Due to the chosen study design, it remains unresolved to what extent e.g. shortened reaction times and smaller conflict scores that were observed with both medications reflect practice or medication effects. The differential pattern of MPH vs. ATX effects on attentional functions in children with ADHD may be explained by the dopaminergic effects of MPH within the cortico-striato-thalamo-cortical circuit.

A roadmap for the development and validation of event-related potential biomarkers in schizophrenia research

New efforts to develop treatments for cognitive dysfunction in mental illnesses would benefit enormously from biomarkers that provide sensitive and reliable measures of the neural events underlying cognition. Here, we evaluate the promise of event-related potentials (ERPs) as biomarkers of cognitive dysfunction in schizophrenia. We conclude that ERPs have several desirable properties: (1) they provide a direct measure of electrical activity during neurotransmission; (2) their high temporal resolutions make it possible to measure neural synchrony and oscillations; (3) they are relatively inexpensive and convenient to record; (4) animal models are readily available for several ERP components; (5) decades of research has established the sensitivity and reliability of ERP measures in psychiatric illnesses; and 6) feasibility of large N (>500) multisite studies has been demonstrated for key measures. Consequently, ERPs may be useful for identifying endophenotypes and defining treatment targets, for evaluating new compounds in animals and in humans, and for identifying individuals who are good candidates for early interventions or for specific treatments. However, several challenges must be overcome before ERPs gain widespread use as biomarkers in schizophrenia research, and we make several recommendations for the research that is necessary to develop and validate ERP-based biomarkers that can have a real impact on treatment development.

How human electrophysiology informs psychopharmacology: from bottom-up driven processing to top-down control

This review surveys human event-related brain potential (ERP) and event-related magnetic field (ERF) approaches to psychopharmacology and psychopathology, and the way in which they complement behavioral studies and other neuroimaging modalities. The major paradigms involving ERP/ERF are P50 suppression, loudness-dependent auditory evoked potential (LDAEP), mismatch negativity (MMN), P300, mental chronometry, inhibitory control, and conflict processing (eg, error-related negativity (ERN)). Together these paradigms cover a range of more bottom-up driven to more top-down controlled processes. A number of relationships between the major neurotransmitter systems and electrocortical mechanisms are highlighted. These include the role of dopamine in conflict processing, and perceptual processing vs motor preparation; the role of serotonin in P50 suppression, LDAEP, and MMN; glutamate/NMDA and MMN; and the role of acetylcholine in P300 generation and memory-related processes. A preliminary taxonomy for these relationships is provided, which should be helpful in attuning possible new treatments or new applications of existing treatments to various disorders.

Attention-deficit/hyperactivity disorder: using P300 topography to choose optimal treatment

Attention-deficit/hyperactivity disorder is the most prevalent behavioral disorder in children, and persists into adulthood. Stimulants (methylphenidate and amphetamines) with dopaminergic mechanisms are the most commonly used pharmacological treatment. Nonselective (desipramine and imipramine) and selective (atomoxetine) norepinephrine reuptake inhibitors can also be effective. What constitutes a sufficient response to treatment? Too often a partial response, leaving the patient symptomatic, is accepted. If response is defined more strictly, allowing for a return to normal, then the usually quoted 70% response rates to any given attention-deficit/hyperactivity disorder medicine drop to approximately 40%. With different medicines and not enough patients responding robustly to any given medicine, we can use medicines sequentially to find the medicine that produces a robust response. Alternatively, P300 topography can be used to select optimal treatment.

Atomoxetine: a novel treatment for child and adult ADHD

Attention deficit hyperactivity disorder (ADHD) is a common chronic condition with childhood onset that can continue into adulthood. Medication is a fundamental element in the management of this disorder. Atomoxetine is the newest nonstimulant medication approved by the United States Food and Drug Administration (FDA) for the treatment of ADHD. It is the only nonstimulant medication approved by the FDA for treatment of adult ADHD. Atomoxetine is a norepinephrine reuptake inhibitor that selectively inhibits the presynaptic norepinephrine transporter. A growing body of literature supports the use of atomoxetine both in children and adults with ADHD. This paper summarizes information from the literature about atomoxetine, including pharmacokinetics, pharmacodynamics, clinical trials, dosing, and side-effects.

Attention-deficit/hyperactivity disorder: Use of cognitive evoked potential (P300) to predict treatment response

OBJECTIVE

To evaluate the use of P300 in predicting treatment response to medicines in patients with Attention-Deficit/Hyperactivity Disorder (ADHD), and to confirm previous reports that 31-electrode mean auditory P300 amplitude (AA) predicts response to atomoxetine; and right fronto-central to parietal AA ratio predicts response to methylphenidate.

METHODS

Efficacy and P300 data from 58 children with ADHD enrolled in a double-blind crossover study using atomoxetine and methylphenidate were analyzed. Robust response was defined as 60% decrease from baseline in the ADHD rating scale. Response was alternately defined as greater than 50% decrease.

RESULTS

Pre-treatment mean 31-electrode AA>6.8 microV predicted response to atomoxetine using both definitions of response. Right fronto-central to parietal AA ratio did not predict response to methylphenidate. A previous report that methylphenidate responders differed from non-responders in pre-treatment AA at T8 was confirmed, and AA at T8>7.65 microV predicted response to methylphenidate. 31-electrode mean P300 visual latency (VL) also predicted response to atomoxetine, as previously reported with imipramine.

CONCLUSIONS

Mean AA predicts response to atomoxetine in ADHD patients. AA at T8 predicts response to methylphenidate. Such predictive tools may allow individually tailored choice of medicine in treatment of ADHD.

SIGNIFICANCE

This allows a more informed decision of which medicine to use for a given patient.

Integrative neuroscience approach to predict ADHD stimulant response

Despite high rates of prescription, little is known about the long-term consequences of stimulant medication therapy for attention-deficit hyperactivity disorder (ADHD) sufferers. Historically, the clinical use of stimulants for ADHD has been based on trial and error before optimal therapy is reached. Concurrently, scientific research on the mechanism of action of stimulants has influenced neurobiological models of ADHD, but has not always informed their prescription. Whilst the two main stimulant types (methylphenidate and dexamphetamine) have numerous similarities, they also differ (slightly) in mechanism and possibly individual response. A further issue relates to differences in cost and availability compounded by the expectation for stimulants to be effective in ameliorating a broad spectrum of ADHD-related symptoms. Thus, there is an increasing need for treating clinicians to prescribe not only the most effective drug, but also the most appropriate dose with the associated release mechanism and schedule for each ADHD patient presented. In this regard, the field is witnessing an emergence of the personalized medicine approach to ADHD, in which treatment decisions are tailored to each individual. This shift requires a new approach to research into treatment response prediction. Given the heterogeneity of ADHD, a profile of information may be required to capture the most sensitive predictors of treatment response in individuals. These profiles will also benefit from the integration of data from clinical rating scales with more direct measures of cognition and brain function. In conclusion, there is a need to establish a more robust normative framework as the baseline for treatment, as well as diagnostic decisions, and as discussed, the growth of integrated neuroscience databases will be important in this regard.

Attention deficit hyperactivity disorder, tics and Tourette's syndrome: the relationship and treatment implications. A commentary

Tourette's Syndrome (TS) is now recognised to be a common childhood onset neurodevelopmental disorder. Attention deficit hyperactivity disorder (ADHD) is also a common childhood disorder. There are many cases in which the two disorders are comorbid. The reasons for this are unclear, but the comorbidity does not necessarily point to one genetic cause. Sleep is also often disturbed in individuals with TS and ADHD. The treatment implications of ADHD in the setting of tics or TS are important. Clonidine is suggested as a first line treatment. It was once thought that stimulants were contraindicated in the treatment of ADHD in the setting of TS, whereas it is suggested that they may be safe, but should be used judiciously. In addition, it was once thought that the combination of stimulants and clonidine was contraindicated, but from a large study the combination does appear to be safe. A relatively new medication for ADHD is atomoxetine, and although not documented widely in the setting of tics and TS, it may prove useful in this setting; further research is required. This commentary briefly discusses the comorbidity between TS and ADHD and offers treatment suggestions.