Introduction to the special issue on psychiatric prevention

The overwhelming burden imposed on the public health by neuropsychiatric conditions is undeniable. Recent estimates suggest that as a group these neuropsychiatric conditions are the second leading cause of disability worldwide as measured by the metric of disability adjusted life years (DALYs). A DALY, which is the sum of the years of life lost due to premature mortality plus the years lost due to disability or incident cases of the disease, can be thought of simply as the number of lost years of ‘healthy’ life. Given that neuropsychiatric conditions account for over 10% of the DALYs in both the developed and developing world, the burden is clearly shared across the spectrum of societies around the globe (http://www.who.int/healthinfo/bodgbd2002revised/en/index.html). Thus, there is significant motivation from all quarters to develop effective strategies for preventing these conditions before they have a chance to cause untold problems.

In this edition of the International Review of Psychiatry we present a series of reviews that discuss progress that has been made in the development of prevention strategies for a range of neuropsychiatric conditions that afflict human populations across the life span. These range from reviews on the prevention of conduct disorder in children by Powell and colleagues all the way to the prevention of Alzheimer's dementia in the elderly by Szekely and colleagues. In between, there are reviews on the prevention of some of the more common major psychopathologies including anxiety disorders by Bienvenu and colleagues, depression by Barrera and colleagues, and schizophrenia by Yung and colleagues. In addition, there are reviews on the prevention of substance abuse by Botvin and colleagues, cognitive dysfunction in adults due to lead by Schwartz and colleagues, and suicide, the most dramatic and measurable consequence of neuropsychopathology, by Brown and colleagues. Although the reviews cover a diverse range of conditions, they all highlight the special challenges in developing effective preventions for neuropsychiatric conditions and the latest advances that have been made in overcoming these challenges.

Historically, prevention strategies have been classified as either primary, secondary, or tertiary (Caplan, [1964]). In this classification scheme, primary preventions are aimed at decreasing the incidence of a disorder by delaying or preventing its onset, secondary preventions include efforts to reduce the prevalence by early identification of persons with relevant risk factors, and tertiary preventions seek to reduce disabilities associated with an existing disorder. In 1994 the Institute of Medicine proposed competing terminology for classifying interventions along a continuum of care including prevention, treatment, and maintenance (Mrazek & Haggerty, [1994]). Within this conceptualization, preventions are reserved for interventions that occur prior to initial onset of a disorder, and they are classified as either universal, selected, or indicated (Gordon, [1983]). Universal preventions are geared towards the general population, selective preventions are directed towards groups of people who have risk factors for a disorder but do not show any current symptoms, and indicated preventions are targeted to individuals with minimal symptoms foreshadowing full-blown disorder. Both classification schemes have utility, because each provides a unique framework to describe the prevention strategies that are available and illuminate new targets along a disease trajectory that may be amenable to further interventions. The review papers in this edition rely on one or the other of these classification schemes to show that prevention strategies have been or are being developed at all levels for the different neuropsychiatric conditions.

A common theme running through all the reviews, either explicitly or implicitly, is the fundamental importance of the public health model and the developmental perspective for developing effective prevention strategies that target the different levels of neuropsychiatric conditions. The public health model offers a useful framework for how to develop such prevention strategies by following an organized series of steps that include 1) defining the problem, 2) identifying risk and protective factors, 3) developing, implementing, and testing interventions, and 4) ensuring the widespread adoption of evidence-based practices. In addition to merely laying out the steps that need to be taken, the public health model provides the epidemiologic tools necessary to achieve each of these steps. These tools include observational studies to define the extent of the problem and identify risk and protective factors that may serve as targets for intervention; randomized studies to test interventions for both efficacy in highly controlled settings and effectiveness in the more chaotic real world environment; and policy studies to examine the extent to which proven interventions are available and utilized by those who need them the most. Each of the review papers in this edition devotes considerable effort to describing the latest findings from the observational and randomized studies of the different neuropsychiatric conditions. Less effort, however, is spent discussing the policy implications of these findings. As advances are made and more definitive prevention strategies are identified, the policy implications will become more important to consider, but such considerations will have to be left to a future edition of this journal.

With the neuropsychiatric conditions reviewed in this edition, the developmental perspective is especially important to the successful implementation of the public health model for several key reasons. First, these conditions typically have insidious and chronic courses that pass through several phases. As a result, the efficacy of an intervention may crucially depend upon when it is administered during the course of the condition. It may be that some interventions work at one phase but have no effect, or even an aggravating effect, at another. This point is highlighted in several of the reviews. For example, in their review of substance abuse, Botvin and colleagues note that the general pattern of transitions in use and abuse of illicit substances is inextricably linked with developmental transitions in adolescence. As a result, they write, ‘Knowledge regarding the developmental progression of substance use during adolescence and early adulthood is important because it can guide the focus and timing of preventive interventions’. This appears to be also true of disease of aging where the course of disease is linked not to neurodevelopment per se but instead to neurodegeneration. In their review of Alzheimer's disease, Szekely and colleagues cite evidence that certain pharmacologic agents may have a neuroprotective effect if taken in the asymptomatic, latent phase of the disease, but accelerate the deteriorating course if taken later after the disease has been clinically established.

Another key reason for the importance of the developmental perspective is because it can help to clarify the ways in which certain inventions aimed at earlier phases of a condition may have a range of salubrious consequences downstream. Powell and colleagues make this point convincingly in their review of conduct disorder. They describe a ‘stacking’ of risk factors whereby early conduct problems lead to worsening trajectories because of an accumulation of additional liabilities as a result of negative behaviours creating disruptions in the social environment which in turn further exacerbate the problems. Indeed, childhood conduct problems have been found to precede almost all categories of adult psychopathologies, presumably through such mechanisms. Consequently, early interventions targeted at conduct problems may improve developmental trajectories and ultimately lead to benefits on reducing a number of later disturbances. Yung and colleagues make a similar point in their review on schizophrenia. They describe how an outbreak of psychotic illness can lead to a wide range of psychosocial consequences, such as dropping out of school, which can exacerbate developmental trajectories and worsen the course of illness. Thus, interventions aimed at those who are at high risk of such an outbreak can minimize the psychosocial damage and collateral impact on the long-term outcomes. The nature and extent of the benefits of such preventions can only be appreciated through an appropriate developmental perspective of the different neuropsychiatric conditions and their negative sequelae as they unfold over the life course. Understanding the constantly changing individual within the context of an ever-changing environment as it impacts on the course and consequences of neuropsychiatric conditions is clearly a key to successful prevention.

The review papers in this edition offer hope that by following the public health model and adopting an appropriately aligned developmental perspective we have been and will continue to make significant progress in developing effective prevention strategies for the range of neuropsychiatric conditions that occur across the life span. These strategies target all areas of opportunity, and include primary, secondary, and tertiary, or alternatively, universal, selected, and indicated interventions. However, further research is clearly needed if we want to fulfill the promise of the public health model and translate new prevention strategies into reduced burden of disease around the globe. Given that the neuropsychiatric conditions remain on the top 10 list of most disabling conditions around the world, much work still needs to be done.