Current operational diagnostic systems have substantial limitations for lifetime diagnostic classification of bipolar spectrum disorders. Issues include: (1) The diagnostic system for bipolar disorder is difficult to operationalize the integration of diverse episodes of psychopathology, (2) Hierarchies lead to loss of information, (3) Boundaries between diagnostic categories are often arbitrary, (4) Boundaries between categories usually require a major element of subjective interpretation, (5) Available diagnostic categories are relatively unhelpful in distinguishing severity, (6) "Not Otherwise Specified (NOS)" categories are highly heterogeneous, (7) Subclinical cases are not accommodated usefully within the current diagnostic categories. This latter limitation is particularly pertinent in the context of the increasing evidence for the existence of a broader bipolar spectrum than has been acknowledged within existing classifications.

Method

We have developed a numerical rating system, the Bipolar Affective Disorder Dimension Scale, BADDS, that can be used as an adjunct to conventional best-estimate lifetime diagnostic procedures. The scale definitions were informed by (a) the current concepts of mood syndrome recognized within DSMIV and ICD10, (b) the literature regarding severity of episodes, and (c) our own clinical experience. We undertook an iterative process in which we initially agreed scale definitions, piloted their use on sets of cases and made modifications to improve utility and reliability.

BADDS (the Bipolar Affective Disorder Dimension Scale) has four dimensions, each rated as an integer on a 0 – 100 scale, that measure four key domains of lifetime psychopathology: Mania (M), Depression (D), Psychosis (P) and Incongruence (I). In our experience it is easy to learn, straightforward to use, has excellent inter-rater reliability and retains the key information required to make diagnoses according to DSMIV and ICD10.

Use of BADDS (the Bipolar Affective Disorder Dimension Scale) as an adjunct to conventional categorical diagnosis provides a richer description of lifetime psychopathology that (a) can accommodate sub-clinical features, (b) discriminate between illness severity amongst individuals within a single conventional diagnostic category, and (c) demonstrate the similarity between the illness experience of individuals who have been classified into different disease categories but whose illnesses both fall near the boundaries between the two categories. BADDS may be useful for researchers and clinicians who are interested in description and classification of lifetime psychopathology of individuals with disorders lying on the bipolar spectrum.

During the course of our family-genetic studies of Bipolar Disorder we became aware of the need for a relatively simple dimensional rating scheme that can be used to provide summary measures of several key areas of lifetime psychopathology relevant to characterization of individuals with Bipolar spectrum illness.

The operational diagnostic systems, such as RDC [1], DSMIV [2] and ICD10 [3], that have been developed over the last 30 years are widely used by clinicians and researchers and have been an important methodological advance over earlier, non-structured approaches [4]. Although open to a variety of criticisms and unlikely to map directly onto the pathophysiology of the disorders, the operational approach is relatively simple, provides acceptable levels of reliability and is useful for communication and decision making regarding management, research and service provision. In most cases the categories defined are informed by a broad range of research data and are revised at regular intervals to take account of new findings and concepts as they emerge.

However, for clinicians and researchers, such as ourselves, interested in disorders lying within the Bipolar spectrum there are several problems in using the current systems for lifetime diagnosis. These include:

1) It is difficult to operationalize the integration of diverse episodes of psychopathology – The operational systems perform best for categorizing a discrete, well-delineated single episode of psychopathology – for example, there are clear-cut criteria to define episodes of mania and major depression. However, a lifetime diagnosis requires integration of the lifetime experience of psychopathology and the criteria used are much less easy to operationalize, typically requiring judgements about the balance between different types of episode [4].

2) Hierarchies lead to loss of information – The existence of explicit, or implicit, hierarchies creates the situation in which certain symptoms "trump" others. For example, an individual can have a diagnosis of DSMIV Schizophrenia despite having had more episodes of mania during his or her lifetime than another individual with a diagnosis of Bipolar I Disorder. For those interested in Bipolarity, this results in a serious loss of important information.

3) Boundaries between diagnostic categories are often arbitrary – Although there is usually a plausible evidence base and/or conceptual basis to support the separation into distinct diagnostic categories, the criteria used to define the boundaries between categories is almost always arbitrary. For example, the level of impairment defines the boundary between Bipolar I and II Disorders – it is most implausible that any specific level of impairment could neatly carve the boundary between distinct disorders. Similarly, in DSMIV the boundary between Bipolar I Disorder and Schizoaffective Disorder, Bipolar Type is defined by the precise timing of occurrence of psychotic symptoms outside of an affective episode. Table 1 lists some key diagnostic boundaries relating to bipolar spectrum disorders and the criteria used in making diagnostic decisions at these boundaries.

4) Boundaries between categories usually require a major element of subjective interpretation – Most of the key boundaries for diagnoses within the Bipolar spectrum require judgements about severity and/or the balance of symptomatology. This substantial subjective element reduces reliability and, as commonsense suggests and everyone who has ever participated in formal reliability exercises knows, cases lying near diagnostic boundaries contribute most of the diagnostic disagreements.

5) Available diagnostic categories are relatively unhelpful in distinguishing severity – No distinction is made between an individual that just meets the threshold for a specific category and another individual that has had multiple severe episodes.

6) Subclinical cases are not accommodated usefully within the current diagnostic categories – An individual who has a DSMIV Diagnosis of Major Depressive Disorder may have experienced multiple mild sub-hypomanic episodes. Indeed, it is being increasingly recognized that the bipolar spectrum extends well beyond the traditional Bipolar I and II categories and includes many individuals with formal diagnoses of unipolar major depression under current operational systems [5,6]. For those interested in bipolarity this is wasteful of information.

7) "Not Otherwise Specified (NOS)" categories are highly heterogeneous – Because of the need for a catch-all category that can accommodate the set of cases not fitting the other operational criteria, the NOS categories in operational systems may include a wide range of types of case ranging between the mild and the severe. Thus, such categories provide little information about the lifetime psychopathology of individuals having the diagnosis.

Dimensional classifications offer an alternative to the conventional categorical approach and have the potential to address many of the issues listed above [7]. Dimensional classifications are not a new idea but have not in the past been widely adopted by either the clinical or research community. Some of the disadvantages, which have impeded widespread use in clinical and research settings in psychiatry, stem from their relative complexity – leading to difficulty in use and interpretation in areas such as communication and decisions regarding management and services.

No suitable dimensional instrument was already available for us to use within our own research on bipolar spectrum disorders.