Classification

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CHAPTER 3 Classification

The classification of psychiatric disorders has been subject to changes over the decades. The two most well accepted and widely used current systems are the World Health Organization’s International Classification of Diseases, tenth edition (ICD–10), and the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, fourth edition, revised (DSM–IVTR). These two classification systems differ in a number of important ways (see Table 3.1), but in terms of the psychiatric disorders they describe, there is rather more congruence than dissonance.

TABLE 3.1 Differences between DSM–IVTR and ICD–10

DSM–IVTR	ICD–10
US-based, published by the American Psychiatric Association, but has wide acceptance around the globe	Published by the World Health Organization; international perspective, and encompasses a diversity of opinion, including from a developing country perspective
Not part of a general medical classification system	Part of a general medical classification system
One version only	Clinical and research versions
Atheoretical	Groupings (‘blocks’) on the basis of presumed shared aetiologies
Multiaxial, with personality disorders on a separate axis (Axis II)	Personality disorders and intellectual disability (mental retardation) not on a separate axis
Global functioning assessed using the Global Assessment of Functioning (GAF) Scale	Disability assessed using the Disability Assessment Schedule (WHO–DAS)

One feature of both systems is that they provide operational criteria that rule diagnosis (ICD–10 applies operational criteria only in its research version). Operational criteria essentially provide a checklist of symptoms and signs, a proportion of which need to be endorsed for the subject to be considered a ‘case’; there are also usually some exclusionary items, such as a clear organic cause for the signs and symptoms. This approach has the downside of to some extent eschewing clinical intuition and judgment, and can lull one into a false sense of security regarding the validity of the constructs they describe. Indeed, none of the disorders in the nosologies are necessarily ‘true’ entities, and the boundaries of many are permeable. Also, there is a danger of labelling individuals according to their diagnosis, with all the associated downsides. Arguably, the psychiatric formulation is a much more satisfactory approach to understanding the individual and why they are presenting with certain symptoms at a specific time (see Ch 1).

However, operational criteria are, in the main, fairly reliable, at least in terms of interrater reliability. There is also a major advantage that they ease communication between mental health professionals (and others), such that one can at least be assured that different people mean much the same thing when they apply a diagnostic label.

The approach taken in this book is a pragmatic one, with both ICD–10 and DSM–IVTR criteria being outlined for each of the major disorders. The grouping of disorders, as described here, is largely congruent with both ICD–10 and DSM–IVTR, but also reflects the influential ‘hierarchical’ model espoused by Graham Foulds.

The pragmatic classification system

Figure 3.1 provides a schematic representation of the major psychiatric disorders in adults. A number of general issues should be noted:

1. There is an implied hierarchy, such that one ‘drills down’ from top to bottom of the pyramid, eliciting pertinent signs and symptoms in turn. Of course, this is not always compatible with clinical interviewing practice, and more often than not clinicians will hone in on the major presenting symptom set first, and then turn to the others. Also, simply making a diagnosis of, for example, schizophrenia, should not stop enquiry about mood and anxiety and other symptoms: indeed, such comorbidities are very common in psychiatry. There is a danger, for example, in making a diagnosis of schizophrenia and then interpreting social withdrawal behaviour as negative symptoms of that illness, when it might actually be due to social anxiety disorder, with very different treatment implications.

2. ‘Organic’ disorders are at the top of the pyramid. This reinforces the importance of always asking oneself whether a set of presenting symptoms could potentially be either caused by, precipitated by, or perpetuated by, an organic condition (see Chs 2 and 4). Again, this is crucial as organic disorders require specific treatments, and can be dangerous if not adequately dealt with.

3. The lines between sets of disorders are presented as solid and this implies a level of delineation that is far from reality. Indeed, many of the boundaries are very fuzzy, with patients presenting with sets of symptoms of two adjoining sets. For example, schizoaffective disorder is a rather loose quasi-category spanning schizophrenia and bipolar disorder (and perhaps unipolar depression), while many of the anxiety disorders have substantial depressive comorbidity.

4. The sizes of each section of the pyramid can roughly be seen to represent the population prevalence of each disorder. Thus, schizophrenia and related disorders afflict some 0.5–1.0% of the population; bipolar spectrum disorders, 2.0–4.0%; depressive disorders, 10–15%; and anxiety and somatoform disorders, over 20%.

5. The ‘base’ of the pyramid represents personality disorders. This is more compatible with the ICD–10 conceptualisation than DSM–IVTR, as the latter places personality disorders on a separate axis (Axis II). However, the point is made that personality predispositions and vulnerabilities both flavour and underpin many Axis I disorders, and arguably a personality disorder diagnosis should not be made without exclusion of active Axis I pathology (see Ch 12).

FIGURE 3.1 Overview of psychiatric disorders (adult)

It should also be noted that this schematic applies to adult psychopathology, and child and adolescent psychiatry adopts a somewhat different approach (see Ch 16). Finally, the schematic does not explicitly include the addictive disorders (see Ch 20), though they can be subsumed under the ‘organic’ rubric.

Organic disorders

In clinical practice, it is vital to examine each patient physically, and to perform laboratory tests where indicated (see Ch 2). One can consider organic factors as:

Causal. The factor is sufficient to cause the psychiatric symptoms (e.g. a temporal lobe tumour presenting as a post-ictal psychosis).

Precipitating. For example, cannabis can precipitate a panic attack in vulnerable individuals, in part at least because of its propensity to induce tachycardia.

Perpetuating. For example, thyrotoxicosis can contribute to ongoing anxiety symptoms.

The organic disorders can themselves be classified, as shown in Box 3.1 (see Ch 4 for more details).

BOX 3.1 Broad classifi cation of organic factors

Organic disorders can be classified as:

• exogenous (e.g. imbibed amphetamines producing a manic syndrome), and

• endogenous, either inside the central nervous system (e.g. temporal lobe tumour presenting with psychotic symptoms) or outside the central nervous system (somatic) (e.g. myxoedema presenting with psychosis).

Schizophrenia and related disorders

Schizophrenia itself is at the core of this group. As discussed in Chapter 5, it is a disorder characterised by sets of symptoms in three main domains—namely, positive (delusions and hallucinations), negative (apathy, withdrawal, restriction of affect) and disorganisation (disorganised thoughts and actions; inappropriate affect). Cognitive impairment is also often part of the illness. DSM–IVTR requires a 6-month duration of symptoms (2 weeks of which should be ‘positive’ symptoms), while ICD–10 has an overall 1-month duration requirement.

For disorders characterised by features of schizophrenia (see Box 3.2), but of briefer duration, various terms are applied, including schizophreniform psychosis (DSM–IVTR), brief reactive psychosis (Scandinavia) and bouffee delirante (France).

BOX 3.2 Schizophrenia and related disorders

The disorders are:

• schizophrenia

• schizophreniform psychosis

• delusional disorder, and

• schizoaffective disorder (on the border between schizophrenia and the affective disorders).

Delusional disorders are characterised by psychotic symptoms, which are to some extent ‘understandable’ and not bizarre (e.g. of marital infidelity; or of illness—monosymptomatic hypochondriacal delusions, or delusional disorder, somatic subtype).

On the border between schizophrenia and the affective disorders lies schizoaffective disorder, with an admixture of features of both sets of disorders. In DSM–IVTR, by definition, the features need to occur separately from each other, but other conceptualisations are less stringent and in clinical practice a schizoaffective label is often applied when patients have an admixture of mood and psychotic symptoms that do not lend themselves readily to either a schizophrenia or mood disorder label. This includes mood disorders with ‘mood incongruent’ delusions (i.e. the delusions are not explicable in terms of current mood state).

Bipolar spectrum disorders

Bipolar disorder was originally delineated along with unipolar mania, as distinct from unipolar depression. Nowadays, unipolar mania has been subsumed under the bipolar label. Thus, bipolar disorder, as detailed in Chapter 7, is characterised by episodes of mania (bipolar I) or hypomania (bipolar II): mania is a more severe form of hypomania, by definition requiring psychiatric treatment. More often than not sufferers also experience depressive episodes, which often are severe and prolonged, and carry significant morbidity and mortality (see Box 3.3).

BOX 3.3 Bipolar spectrum disorders

Disorders include:

• bipolar I: mania +/– depression

• bipolar II: hypomania +/– depression

• bipolar III: mania/hypomania in setting of antidepressant exposure, and

• cyclothymia: mood swings (up and down) not severe enough to meet the criteria for bipolar disorder.

There is some debate about the nosological status of patients who manifest manic or hypomanic symptoms only on exposure to antidepressant drugs or ECT. They have been labelled bipolar III by some authors. Presumably, such individuals carry a bipolar predisposition, but only manifest the illness with a suitable stimulus.

Cyclothymia used to be considered a personality disorder, but sufferers appear to respond to mood stabilising drugs; hence, it has been moved from Axis II to Axis I in DSM–IVTR.

Depressive disorders

No entirely satisfactory classification of the depressive disorders has yet been arrived at (see Box 3.4). For so-called major depressive disorder (MDD), DSM–IVTR stipulates a 2-week illness duration with features that must include pervasive low mood and/or loss of interest/pleasure. Dysthymia is a term reserved for those patients who have a chronic low-grade depression present on more days than not, for at least 2 years. Superimposed major depressive episodes in people with dysthymia is sometimes referred to as double depression.

Various descriptors of a major depressive episode are allowed—namely, mild, moderate or severe. Also, melancholic features and the presence of ‘mood congruent’ psychotic symptoms should be stipulated; ‘mood incongruent’ symptoms suggest a diagnosis of schizoaffective disorder, or schizophrenia with a mood disorder.

Anxiety and somatoform disorders

The anxiety and somatoform disorders are divided here in a pragmatic manner, with a view to treatment implications (see Box 3.5). Further details can be found in Chapters 8, 9, 10 and 11.

Panic disorder is characterised by repeated panic attacks, at least half of which occur ‘out of the blue’. Once panics are linked to specific situations (e.g. crowds in agoraphobia, social situations in social phobia) or things (e.g. spiders or snakes in specific phobia), and there is consequent avoidance of those situations or things to an extent functioning is impaired, they can be considered phobic disorders. DSM–IVTR links panic with agoraphobia in particular, but panics can occur in any of the phobic disorders.

Generalised anxiety disorder is something of a residual category with very high comorbidity with depression: some authorities believe it should be subsumed under the depressive disorders.

Post-traumatic syndromes in DSM–IVTR include an acute stress disorder (less than 1 month), and a more enduring (greater than 1 month) post-traumatic stress disorder. Symptoms are similar in each (see Box 3.6), but dissociation is given particular prominence in acute stress disorder. ICD–10 does not formally distinguish acute from more prolonged stress reactions.

BOX 3.6 Symptoms of post-traumatic stress disorder (PTSD)

Symptoms include:

• reliving experiences (e.g. dreams and nightmares)

• hyperarousal, including an exaggerated startle response, and

• avoidance behaviours (of situations or things that serve as reminders of the traumatic event) and emotional numbing.

The nature of the stressor in the post-traumatic syndromes has been subject to debate: currently, DSM–IVTR stipulates the stressor should be such that it is a perceived threat to the life or physical integrity of the individual, their family, or those around them.

The obsessive-compulsive spectrum disorders are discussed in some detail in Chapter 9. Suffice to say here that there is a current vogue for grouping together a number of disorders into a so-called obsessive-compulsive spectrum (OCS), on the basis of shared symptomatology and treatment response. In fact, the veracity of the putative spectrum has been challenged, but for ease of discussion we can consider three main groupings, as shown in Figure 9.1. Obsessive-compulsive disorder (OCD) itself sits at the centre of this grouping. It is characterised by intrusive thoughts (obsessions) and associated compulsive acts aimed at reducing the anxiety associated with the thoughts. As outlined in Chapter 9, OCD is arguably itself a heterogeneous group of conditions, rather than an entity; certainly, hoarding does not sit easily under this label.

The somatoform disorders are a highly contentious and unsatisfactory grouping of disorders that ostensibly have somatisation at their core. They are discussed further in Chapter 11. DSM–IVTR includes body dysmorphic disorder here, but this approach has little to support it, and we have placed it in the OCD spectrum.