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The most common concept of borderline is based on a continuum or dimensional model of psychopathology, as is represented in Figure 1. In simplest terms, behavior or psychological functioning is viewed as ranging from normal to severely psychotic. Menninger has used this model exclusively in classifying mental disorders in his book The Vital Balance (Menninger, Mayman, and Pruyser, 1963). Neuroses and character disorder are placed toward the normal end of this continuum. Borderline refers to a disorder with greater severity than neurosis and character disorder but less severity than psychosis. This concept is used by Grinker, Werbie, and Drye (1968). Their four subgroups can be considered as defining subsections on a segment of this continuum, with their Group I on the border with psychoses and Group IV on the border with neuroses.
A second model-the typological model-suggests that psychopathology can best be organized into discrete groups not representing a continuum or having any other specific relation to each other (see Figure 2). In this model, nosologic groups are delineated from each other and from normals on the basis of a supposedly qualitative unique characteristic feature. Any pathologic manifestation could range from mild to marked within the group, but the presence of distinguishing features rather than their severity is critical to diagnosis. This model does not imply that no similar psychopathologic features are to be found between groups (e.g., anxiety is almost ubiquitous across diagnostic classes), only that distinguishing features identify patients as belonging to a discrete class.
The theoretical implications of these two concepts are quite different. The first model encourages a search for points on the continuum which can usefully be defined and distinguished from other points. One assumes there will be confusing cases at the interface between any two defined points, and that locating such a boundary case in either group would not be entirely misleading. In contrast, a typologic or discontinuous model of psychopathology does not allow for the intermediate case, and hence the implications are more drastic. An incorrect classification would be entirely misleading, rather than simply underestimating or overestimating the severity of psychopathology. There could be confusing cases, however, either because the disease is only partially manifest or because the patient was simultaneously afflicted with two illnesses.
Considerable evidence has now emerged suggesting some discrete classes of psychopathology. Genetic studies (adoptive, cross-fostering, and family-tree) document that manic-depressive and schizophrenic illness are discrete, and this distinction is supported by differential psychopharmacologic responsivity. On the other hand, if one looks at these two illnesses from a descriptive or an egopsychologic point of view, phenomenologic and ontogenetic observations can be readily conceptualized on a continuum. The concept of schizophrenia spectrum (Kety et al., 1968), derived from genetic investigations, lends support to a continuous model of psychopathology.
In the continuum model the question is whether borderline is a useful segment to delineate. There is no question about the existence of a borderline as there is a border between any two sequential points. The question is pragmatic: Does defining the characteristics of the border provide useful information in terms of etiology, course, or treatment? Is assigning a borderline diagnosis more helpful than diagnosing these patients as either neurotic or psychotic, or relegating them to an uncertain diagnostic status?
If we use a discontinuous model, on the other hand, then we must prove that such a group exists. Nosology implies a capacity to generalize from group membership. Assignment to an invalid class would be totally misleading.
The use of borderline as a diagnosis if this category is inadequately defined has different implications in the two models discussed. On a continuum model, a poorly defined point would lead to sloppy diagnostic practices reducing the usefulness of the better-defined surrounding points. In the discontinuous model a poorly defined entity would have little chance of being validated, hence its existence as well as usefulness would be in question.
A third model for classification combines the properties of the continuum and typological approaches. Such a combined or mixed model provides the means for integrating the presently available conflicting data relevant to psychiatric nosology. A mixed model can define two levels-a continuous and a discrete level- allowing one to conceptualize disordered ego functioning and character development along a severity continuum but hypothesizing that at certain segments of this continuum psychopathologic manifestations (e.g., highly distinguishing signs and symptoms) may arise to identify discrete nosologic classes.
Currently we favor a mixed model
in our project, as do most of the workers in the field. In simplest terms,
we are dealing with the proposition that there is a group of patients less well
put together than neurotic or character-disorder patients, yet not so sick or
disorganized as schizophrenic or other psychotic patients. The basic hypothesis
is that such a group of patients can be defined with clinical criteria, and that
a group so delineated will prove to be different from neurotic and character-disorder
patients on the one hand, and schizophrenic patients on the other, in terms of
manifest psychopathology, past history, course and outcome, pharmacologic responsivity,
and genetic loading. We thus use a continuous model in identifying patients as
borderline, but we then examine the proposition that patients so diagnosed will,
in fact, comprise a discrete nosologic class.