Long established as the preeminent source in its field, the eagerly anticipated fifth edition of Dr Stahl's essential textbook of psychopharmacology is here! With its use of icons and figures that form Dr Stahl's unique 'visual language', the book is the single most readable source of information on disease and drug mechanisms for all students and mental health professionals seeking to understand and utilize current therapeutics, and to anticipate the future for novel medications. Every aspect of the book has been updated, with the clarity of explanation that only Dr Stahl can bring.
Attention Deficit Hyperactivity Disorder and Its Treatment
Attention deficit hyperactivity disorder (ADHD) is not just a disorder of “attention,” nor does it have to include “hyperactivity.” Paradigm shifts are altering the landscape for treatment options across the full range of ADHD symptoms, from inattention to impulsivity to hyperactivity, as well as across all the waking hours and across the whole lifespan, from young children through adulthood. This chapter will provide an overview of the psychopharmacology of ADHD, including only short discussions of the symptoms of ADHD. The mechanism of action of treatments classically called stimulants and nonstimulants for ADHD will be emphasized. Information on the full clinical descriptions and formal criteria for how to diagnose and rate ADHD and its symptoms should be obtained by consulting standard reference sources. The discussion here will emphasize the links between various brain circuits and their neurotransmitters with the various symptoms and comorbidities of ADHD and how these are linked to effective psychopharmacological treatments. The goal of this chapter is to acquaint the reader with ideas about the clinical and biological aspects of attention, impulsivity, and hyperactivity. For details of doses, side effects, drug interactions, and other issues relevant to the prescribing of drugs for ADHD in clinical practice, the reader should consult standard drug handbooks (such as Stahl’s Essential Psychopharmacology: the Prescriber’s Guide).
ADHD is noted for a trio of symptoms: inattention, hyperactivity, and impulsivity (Figure 11-1). It is currently hypothesized that all these symptoms arise from inefficient information processing in various circuits involving the prefrontal cortex (Figures 11-2 through 11-8). Specifically, the prominent symptom of “inattention” in ADHD can also be described more precisely as “executive dysfunction” and the inability to sustain attention long enough to solve problems. Executive dysfunction is hypothetically linked to inefficient information processing in the dorsolateral prefrontal cortex (DLPFC) (Figures 11-2, 11-3, and 11-7). The DLPFC is activated by a cognitive task known as the n-back test which can be monitored in living patients doing it while in a functional brain scanner (shown in Figure 11-3). Having difficulty in efficiently activating this part of the brain cuts across many psychiatric disorders that share the symptom of executive dysfunction, not just ADHD but also schizophrenia (discussed in Chapter 4), major depression (discussed in Chapter 6), mania (discussed in Chapter 6), anxiety (discussed in Chapter 8), pain (Chapter 9), and disorders of sleep and wakefulness (discussed in Chapter 10). One can see how inefficient information processing in this particular DLPFC circuit, especially when put under a cognitive “load,” can be associated with the same symptom of executive dysfunction and difficulty in sustaining attention and solving problems in many different psychiatric disorders. This is why diagnosis in psychiatry is now progressively moving from describing categorical syndromes that mix together many symptoms to make a diagnosis (as in the DSM and ICD), towards characterizing single symptom dimensions or domains such as executive dysfunction that cut across many psychiatric disorders. The emphasis on symptoms rather than diagnosis is the trend in much of neurobiological research, with the goal of finding better correlates with neuroimaging, biomarkers, and genetics.
Another dimension of executive dysfunction in ADHD is selective inattention, or not being able to focus, and thus differs from problems with sustaining attention described above. The symptom of problems focusing/selective inattention is hypothetically linked to inefficient information processing in a different brain area, namely the dorsal anterior cingulate cortex (dACC) (Figures 11-2, 11-4, and 11-7). The dACC can be activated by tests of selective attention, such as the Stroop test (explained in Figure 11-4). ADHD patients may either fail to activate the dACC when they should be focusing their attention, or they may activate this part of the brain very inefficiently and only with great effort and easy fatiguability.
Other areas of prefrontal cortex that are hypothetically functioning inefficiently in ADHD are the orbital frontal cortex (OFC), linked to symptoms of impulsivity (Figures 11-2, 11-5, and 11–7), and the supplementary motor area, linked to symptoms of motor hyperactivity (Figures 11-2, 11-6, and 11–7). The OFC is hypothetically linked to a wide variety of symptoms that cut across several psychiatric conditions, including impulsivity in ADHD (Figures 11-2, 11-5, and 11-7), impulsivity and violence in schizophrenia (discussed in Chapter 4), suicidality in depression (discussed in Chapter 6), impulsivity in mania (discussed in Chapter 6), and impulsivity/compulsivity in substance abuse and related disorders (discussed in Chapter 13). Impulsive symptoms in other psychiatric conditions commonly comorbid with ADHD are also hypothetically related to the OFC such as conduct disorder, oppositional defiant disorder, and bipolar disorder (Figure 11-8). See Chapter 13 for further discussion of impulsivity and compulsivity in a variety of psychiatric disorders including substance abuse, eating disorders, obsessive–compulsive disorder (OCD), and others.