Prodromes, precursors, and at-risk mental states
It has long been recognized that the onset of the first episode of psychosis may be gradual and preceded by low-grade symptoms and signs retrospectively labeled the “prodrome” (
Keith and Matthews 1991). The term “prodrome” is derived from clinical medicine and refers to the early symptoms and signs of a disease that occur before the obvious characteristic features become manifest (
Yung and Stanley 1989). Measles has previously been used to illustrate this concept (
Yung and McGorry 1996, this issue). In this disease, a nonspecific prodrome of cough and coryza usually precedes the characteristic measles rash by 3 or 4 days. During this prodromal period, a definitive diagnosis of measles cannot be made because the features are not specific to the disease. The symptoms could result from an upper respiratory infection or another disease. However, with the advent of the rash, measles is diagnosed, and the cough and coryza of the previous few days are then retrospectively recognized as the measles prodrome. This example illustrates how the prodrome, a retrospective concept, cannot be defined with certainty prospectively (
Eaton et al. 1995;
Yung and McGorry et al. 1996, this issue).
How then, can we conceptualize the mental state of a person who displays features suggesting an impending disorder, that is, who seems to be in the “prodromal period”?
Eaton and colleagues (1995) have suggested the term 11 precursor signs and symptoms” and defined as “signs and symptoms from a diagnostic cluster that precede disorder but do not predict onset with certainty” (p. 968). Our group has suggested an alternative term, “at-risk mental state,” which implies that the clinical picture will not invariably be followed by full disorder (
McGorry and Singh 1995). The advantage of this term is that it emphasizes that the syndrome represents a
state risk factor for the disorder. That is, at the point when a person has a particular mental state, he or she is at increased risk of onset of the actual disorder. This concept of a state risk factor is to be distinguished from
trait risk factors such as family history and certain biological markers, which confer heightened probability of onset at all times, regardless of the patient’s current mental state (Wolf and Cornblatt, in press).
The idea of state risk factors has analogies in clinical medicine. It is recognized, for instance, that people who experience the characteristic chest pain “angina pectoris” are at increased risk for later acute myocardial infarction (AMI). Angina pain is not as severe as the pain of an infarct and is accompanied by fewer of the features generally associated with infarcts, such as sweating, nausea, vomiting, pallor, and breathlessness. Thus, angina could be seen as an attenuated or subthreshold version of the full-blown AMI, with both conditions having the same underlying pathology of ischemic heart disease and atherosclerosis. The syndrome of “crescendo angina,” which is angina of increasing frequency and severity, is described as a “preinfarction syndrome” indicating high risk of imminent AMI.
This model can be applied to psychotic disorders. Symptoms such as overvalued ideas or vague perceptual abnormalities can be thought of as attenuated forms of psychotic symptoms, indicating increased risk for subsequent psychosis as angina indicates increased risk for subsequent AMI. Likewise, delusional mood can be seen as the equivalent of the preinfarction syndrome. Note that these mental state features must be new phenomena and must be distinguished from schizotypal personality features, which are long-standing and represent a trait risk factor for psychosis (analogous to hypertension’s relationship to AMI). This kind of attenuated or subthreshold model has been used in relation to depressive disorders. Subthreshold depressive symptoms, for example, have been viewed as risk factors for major depressive disorder in children (
Jaycox et al. 1994) and as precursors with a degree of relative risk for major depression in adults (
Eaton et al. 1995).
Another example is transient ischemic attacks (TIAs). These consist of sudden focal neurological abnormalities that settle rapidly within 24 hours with full clinical recovery (
Kistler et al. 1991). They resemble a full-blown stroke but are distinguished from stroke in that they spontaneously resolve. TIAs are known to confer an increased risk of stroke, with an estimated 40 percent of patients with some types of TIA progressing to a complete stroke within 3 years (
Rubenstein and Wayne 1980). As in the above example, the underlying pathology, that of thromboembolic cerebrovascular disease, is the same in TIA and stroke. Again, this model can be used in psychotic disorders. Histories of brief transient episodes of psychotic symptoms that spontaneously resolve have been described occasionally by patients presenting with psychotic disorders (
Faergman 1963;
Jauch and Carpenter 1988). Such transient psychotic symptoms are also known to occur in some people under the influence of certain psychoactive substances such as amphetamines and hallucinogens (
Tsuang et al. 1982;
Vardy and Kay 1983) and cannabis (
McGuire et al. 1994). They have also been noted in patients with some personality disorders such as borderline personality, particularly when the patients are under stress (
Gunderson and Singer 1975;
Vaillant and Perry 1980), and in a proportion of normal individuals who, when subjected to sensory deprivation, temporarily suffer from visual and auditory hallucinations (
Slade 1984). These transient psychotic episodes may indicate increased risk of subsequent psychosis and can be thought of as the “psychosis equivalent” of TIAs.
Defining onset
Identifying symptoms or signs that reliably predict onset would obviously aid attempts to prevent mental disorders. Such specific predictors do not currently exist (
Eaton et al. 1995). In fact, one could argue that if any such risk factors were identified they would be best conceptualized as early phenomena of the disorder itself. For example, a feature that is invariably followed by onset of psychosis might be thought of as part of schizophrenia itself. Researchers would then call the syndrome “prepsychotic schizophrenia” rather than label the feature a “specific prodromal feature,” “specific precursor feature,” or “specific feature in the at-risk mental state.” Identifying the feature should therefore lead to initiation of treatment.
This perspective is of course partly true but not so simple in practice, Again using the model of measles, an early sign of the disease is the presence of Koplik spots, small, white lesions inside the mouth that represent the mucosal manifestation of the skin rash but that precede the rash (
Yung and Stanley 1989). Koplik spots can be thought of as an early feature of the measles disease itself, or a “specific precursor feature.” Skilled clinicians would note their presence in an ailing child and correctly predict the inevitable development of the measles rash. However, clinicians not so knowledgeable or experienced in managing measles patients could easily fail to look for Koplik spots, not detect the spots even if they sought them, or misdiagnose them as, for example, oral candidiasis. Conversely, another patient presenting with cough and coryza might be labeled as having Koplik spots and therefore measles, but not actually have them because of misdiagnosis of another oral lesion such as candidiasis. Hence, false negatives and false positives could occur. For this reason,
clinically detected Koplik spots can be thought of as a measles precursor with high specificity.
The idea of false positive and false negative precursor features can be further illustrated by the TIA example. A migraine might resemble a TIA clinically but have a different underlying pathophysiology and not confer increased risk of stroke; that is, it would be a false positive. Conversely, a TIA might be wrongly labeled as a migraine; hence, this warning sign for impending stroke would be missed.
The Koplik spot equivalent for psychosis generally or for a subtype such as schizophrenia (if defined disorders are in fact biologically meaningful subtypes) would be a very useful entity to identify. A feature that predicted subsequent psychosis in the near future with a high degree of probability could be used to indicate the timing of specific antipsychotic treatment such as neuroleptic medication. Several authors have suggested that certain clinical phenomena have some specificity for subsequent development of psychosis. For example,
Chapman (1966) theorized that a disorder of selective attention and perceptual abnormalities may predict psychosis and called such phenomena “the early symptoms of schizophrenia,” thus conceptualizing these subthreshold symptoms as part of the schizophrenic disorder itself. Others have suggested that a change in the sense of self and the world (
Bowers and Freedman 1966) and suspiciousness (
Cameron 1938;
Conrad 1958) may predict subsequent psychosis.
Huber and colleagues (1980) have suggested that coenaesthesic symptoms and certain cognitive abnormalities (some similar to Chapman’s disorder of selective attention) represent “transition states” preceding psychotic schizophrenia (
Ebel et al. 1989;
Gross 1989) and claim that such “basic symptoms” are primary experiences of psychotic symptoms. If any of these clinical features can be found to be strong predictors of subsequent psychosis, then the prospect of intervention before onset of frank psychosis in schizophrenia and other psychotic disorders may be possible. Such hypotheses therefore need to be tested rigorously.
The onset and course of psychotic disorders are more complex than in measles, which is an “all or nothing” phenomenon; that is, either the full disorder develops or it does not. In psychosis, defining the onset of disorder involves a degree of judgment. One important underlying conceptual consideration is whether psychotic symptoms represent qualitatively different phenomena from normal mental experiences or occur on a continuum with normal experiences, representing quantitative deviations only. Traditionally, schizophrenia and psychotic symptoms have been viewed as discontinuous, qualitatively distinct from normal experiences, and “ultimately un-understandable” (
Jaspers 1923/1963). “These are true illnesses in which a sharp break in the personality occurs, probably the result of a neurophysiological disorder which so far has escaped detection” (
Fish 1985, p. 15). Schizophrenia and psychosis are contrasted with neurotic disorders such as anxiety and depression, in which the definition of “caseness” is made arbitrarily because of a quantitative variation from normal. For example, Falloon states, “the task of identifying schizophrenia is facilitated by the usual presentation of clearly specified florid symptoms that represent a qualitative departure from normal mental phenomena” (
Falloon 1992, p. 6).
Others, however, conceptualize psychotic symptoms such as delusions and hallucinations as part of a continuum with normal and neurotic experiences (
Strauss 1969). Several researchers have investigated subthreshold variants of psychotic symptoms as indicators of “psychosis proneness” or “schizotypy” and found them to occur on a dimension in the general population (
Chapman and Chapman 1980,
1987;
Claridge and Broks 1984). There is also considerable evidence from family members of schizophrenia probands (
Kety et al. 1975) and high-risk followup studies of children of psychotic parents (
Mednick et al. 1987) that certain neurological and psychological abnormalities occur on a spectrum. These factors can be seen as vulnerability markers for schizophrenia or partial expressions of the disorder.
A further possibility is that psychotic symptoms represent quantitative differences at onset but at a later point undergo a qualitative change.
Claridge (1985), drawing an analogy between psychosis and systemic physical disease, noted that hypertension is arbitrarily defined initially as a quantitative change from normal, but that a point is reached when qualitative structural changes occur in various tissues in response to chronic raised blood pressure. Like physical systemic disorders, mental disorders probably require environmental stress and an underlying susceptibility (
Zubin and Spring 1977). Claridge has suggested that as both of these factors are continuous variables then manifestations of disorder occur on a dimension also, from mild or incomplete through severe (
Claridge 1985). Claridge concludes that “a continuity view of psychotic behavior becomes not just feasible but the most probable explanation of currently available evidence” (p. 109) and speculates that there may be a point in the course of the disorder when a qualitative change occurs, as happens in hypertensive disease. The timing and clinical indicators of this point beyond which psychosis will invariably occur are not yet known. Ongoing prospective investigation is needed.
To further complicate matters, attention is increasingly being drawn to the multidimensionality of florid positive symptoms, that is, the degree of preoccupation with delusional beliefs, the intensity and frequency of such delusions, the affects they generate, and so on (
Chadwick and Birchwood 1994;
Chadwick et al. 1994). There is no reason why this conceptualization cannot, or should not, be extended to prodromal phenomena. In fact, it may be that the various dimensions of a particular prodromal symptom have different onsets and developments and are loosely correlated with one another. It may also be that particular aspects of a prodromal symptom are more important for different persons.
The definition of actual timing of onset of schizophrenia and other psychotic disorders has received little attention in the literature. One reason for this is that prospective studies mapping the onset of psychosis are difficult to achieve, and onset features of psychosis are usually described retrospectively. The date of onset of psychosis is usually decided arbitrarily based on a combination of patient and informant data, for example, the time of the first noted auditory hallucination (
Häfner et al. 1992a;
Loebel et al. 1992). Such arbitrary decisions do not address the issues of how long a symptom needs to be present, how often, and to what degree of intensity or impact on functioning. Should the label of psychosis be applied to someone who experiences 1 day of auditory hallucinations several times during that day for a few minutes at a time? Or to someone who has had such symptoms for I hour, or 1 week, or 2 weeks? Do hallucinatory phenomena occur on a spectrum, and if so, when are they considered frankly psychotic? The same questions could be asked of overvalued ideas and delusions. The significance of combinations of symptoms, such as perceptual abnormalities and disorders of thought content, also needs to be clarified. This issue is important in considering when to treat.
It is also likely that the transition from the premorbid state through the prodromal phase to psychosis is not smooth. Fluctuations should be expected to occur, depending on the person’s coping resources, life circumstances, and stress level at the time. As Sullivan stated, “It is never easy to say just when the schizophrenic patient has crossed the line into actual psychosis. In several cases we have found that there had occurred a brief phase of marked psychotic condition some considerable time before the final break” (
Sullivan 1927/1994, p. 137).
The definition of onset of disorder is also relevant to considerations of whether intervention during the putative prodromal phase constitutes primary or secondary prevention. If the prodromal period is considered to be part of the disorder itself, then intervention at this stage would be seen as secondary—albeit early secondary—prevention. If, however, the prodrome is viewed as a separate syndrome conferring heightened but not inevitable risk for psychosis, then intervention would be viewed as primary prevention. The perspective may also depend on the stage of the prodrome. Intervention in an early nonspecific prodrome may be thought of as more likely to be primary prevention, whereas later intervention into a prodrome that has possibly passed the point of a qualitative change may be seen as secondary prevention.
Eaton et al. (1995) addressed this point, stating, “At some point during development, the onset of full-blown disorder becomes inevitable and the prevention efforts are conceptually shifted from primary to secondary” (p. 971). Thus, the “Koplik spot” of psychosis, if it could be found, would indicate the onset of disorder, and intervention at this time would constitute secondary prevention.