ConCeptual and HistoriCal BaCkground

Diagnosis and classification of mood disordersrobert kendell

Abstractthis article covers contemporary classifications of mood disorders,

the problem of boundaries between the different syndromes, the

shortcomings of iCd-10 and dsM-iV, and the diagnosis of mood

disorders.

Keywords classification; depression; diagnosis; dsM-iV; iCd-10; mania;

mood disorders

Historical background

The classification of mood disorders has been controversial ever since the 1920s. In Britain, and to a lesser extent in western Europe, the predominant controversy concerned the validity of the distinction between endogenous and reactive (or neurotic) depressions. To some psychiatrists this was of fundamental importance; to others it was not justified either by their clini-cal experience or by careful studies of unselected populations of patients. In the USA there were similar, though less passionate, disputes between psychiatrists who were convinced they had evi-dence to justify a fundamental distinction between primary and secondary depressions, or between pure depressive disease and depression spectrum disease, and others who remained uncon-vinced.1 Eventually the consensus view was that the empirical evidence, particularly the findings of large research programmes such as the American Collaborative Program on the Psychobi-ology of Depression, did not adequately support any of these attractive dichotomies.

Contemporary classifications of mood disorders

As a result of this, the two important contemporary classifications of mental disorders – ICD-102 and DSM-IV3 – both eschew all fundamental distinctions, except between manic and depressive illnesses, and distinguish between different types of depressive illness largely on the basis of differences in severity, duration and frequency of occurrence. Indeed, ICD-10 comments apologeti-cally that:

Robert Kendell was Professor of Psychiatry at the University of

Edinburgh, Edinburgh, UK. He was also at various times Dean of

the Edinburgh Medical School, President of the Royal College of

Psychiatrists and Chief Medical Officer for Scotland. We are pleased to

reprint his contribution to the first edition, which remains a model of

clarity and as relevant today as when it was first published in 2003.

psYCHiatrY 8:2 4

‘affective disorders are not yet sufficiently understood to allow their classification in a way that is likely to meet with univer-sal approval … nevertheless, a classification must be attempted, and the one presented here is put forward in the hope that it will at least be acceptable, since it was the result of widespread consultation.’

ICD-10 and DSM-IV are both too complex for use in primary care and simplified versions have been developed for primary care settings – ICD-10-PHC and DSM-IV-PC. There is also an international classification – the WONCA (World Organization of Colleges and Academics) system – produced by GPs them-selves. In reality, none of these systems is widely used and most British GPs use either the Read codes or simple terminologies of their own.

The depressions

‘Depression’ is an unsatisfactory term; it is too vague and has too many meanings. In addition to its quite different technical meanings in topography, meteorology and economics, the word is used in psychiatry to describe both a mood and a syndrome, and in both these contexts for anything from fleeting gloom to abject despair, from transient despondency to chronic melancho-lia. Nevertheless, we are stuck with it.

The basic syndrome is called a ‘depressive episode’ in ICD-10 and a ‘major depressive episode’ in DSM-IV. Both sys-tems distinguish three grades of severity (mild, moderate and severe); both require symptoms to have persisted for at least 2 weeks; and both require the presence of several of a list of typi-cal depressive symptoms (lack of energy, impairment of sleep, appetite or concentration, suicidal thoughts, etc.), though nei-ther makes subjective lowering of mood a mandatory require-ment. Both also distinguish, in similar ways, between single and recurrent episodes and make provision for separate iden-tification of what has variously been called the endogenous, endogenomorphic, melancholic or vital syndrome. ICD-10 does so under the title of ‘somatic syndrome’ and DSM-IV uses ‘mel-ancholic features’.

Both classifications also include as distinct disorders dys-thymia (constant or oft-recurring mild depression lasting for at least 2 years) and cyclothymia (instability of mood fluctuating from mild depression to hypomania, also persisting for at least 2 years). Although there are minor differences in the precise definitions of depressive episode and major depression, and also for dysthymia, it has been shown in community surveys that, in practice, concordance between the two systems is quite good.

Manic states

ICD-10 and DSM-IV both use the same term, ‘manic episode’, for the basic syndrome and both require an elevated, expansive or irritable mood for at least 1 week (less if hospital admission supervenes), together with three or four other listed symptoms. Both also distinguish three grades of severity of manic episodes and both use the term ‘bipolar disorder’. Beyond this point, how-ever, there are several subtle, confusing and irritating differences between them, for example in the precise meanings of the terms hypomania and bipolar disorder. DSM also draws a distinction between bipolar I and bipolar II disorders, the former requiring

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ConCeptual and HistoriCal BaCkground

only a single manic (or mixed) episode, the latter requiring at least one major depressive episode preceded or followed by at least one hypomanic episode, but with no history of mania.

The boundary problem

The main obstacle to a better classification of mood disorders, increasingly widely recognized but rarely commented on, is the lack of natural boundaries between the different syndromes. Not only have those who sought to distinguish between qualita-tively different kinds of depressive illness failed to present con-vincing supporting evidence, there is no evidence of any natural boundary between major depression and so-called ‘sub-syndro-mal depression’ (the mild depressive symptoms experienced by most people in response to the vicissitudes of everyday life). Moreover, it is evident that sub-syndromal depression is accom-panied by significant functional impairment as well as being the often undeclared and undetected cause of many consulta-tions in primary care. Nor is the distinction between unipolar (depression only) and bipolar (depression and mania) illness as clear-cut as its originators assumed. Mixed states involving the simultaneous presence of both manic and depressive symp-toms are by no means rare, and at least 10% of bipolar patients are converts from unipolar illness because they experience their first manic illness after three or more episodes of depression. More significantly, although unipolar illness predominates as expected in the first-degree relatives of unipolar probands, it also predominates in the first-degree relatives of bipolar probands.

This implies that all the distinctions drawn within the territory of mood disorders – between different varieties of depression, between depression and normality and even between unipolar and bipolar illness – though undoubtedly useful, and even nec-essary, are largely arbitrary. The same must therefore be true of the formal definitions of the different syndromes provided by ICD-10 and DSM-IV, and in fact apparently minor changes in the wording of these definitions, as occurred for example between DSM-III (1980) and DSM-IV (1994), result in substantial changes in the recorded prevalence of major depression and other syn-dromes in community surveys. The problem, of course, is not unique to mood disorders, or even to psychiatry. The boundar-ies between normality and hypertension, obesity or diabetes are equally arbitrary.

The shortcomings of ICD-10 and DSM-IV

The most frequently voiced criticism of both these nosologies is their abandonment of the concept of melancholia or endogenous depression. Parker, for example, has argued that for the last 20 years depression research has been hindered by the focus on the broad concept of major depression fostered by DSM-III and its successors, and that there are sound reasons for distinguishing both melancholia (defined by the presence of observable psy-chomotor retardation) and psychotic depression (defined by the presence of delusions and hallucinations) from other less differ-entiated depressions.4 In reality, though, the greatest weakness of contemporary classifications of mood disorders is their failure to give adequate recognition to the close, complex relationship between depression and anxiety (see Tables 1 and 2).

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Co-occurrence of anxiety and depression: every experienced psychiatrist, and certainly every GP, knows that a combination of depressive symptoms (such as low mood, lassitude and pessi-mism about the future) and anxious symptoms (such as tension, insomnia and irritability) is extremely common. Indeed, this was confirmed by a recent survey of the UK population, which found this to be the commonest psychiatric syndrome of all. However, this co-occurrence is inadequately recognized by the official nomenclatures.

Strengths and weaknesses of the ICD-10 classification of mood disorders

Strengths

• it is less controversial than its predecessors, iCd-6 to iCd-9

• it was subjected to pilot studies in several countries before

being introduced

• explicit (operational) definitions are provided for clinical and

epidemiological research

• there are no major incompatibilities with dsM-iV

 Weaknesses

• it is unnecessarily complex (36 categories at the three-digit

level and another 12 at the four-digit level)

• Most of the boundaries between its constituent categories

are arbitrary and unvalidated

• there is inadequate recognition of the close, complex

relationship between depressive and anxiety disorders

Table 1

The close (and formally unrecognized) relationship between depressive disorders and anxiety disorders

• Comorbidity is extremely common, particularly in the general

population (in one recent population-based study, the

odds ratios for the co-occurrence of generalized anxiety

disorder, agoraphobia and panic disorder in people meeting

lifetime criteria for major depression were 8.7, 5.2 and 3.7

respectively)

• the most common psychiatric syndrome in the uk adult

population, with a prevalence of 1 in 7, is a mixture of

depressive and anxiety symptoms rather than one or the

other

• abuse (sexual or physical) or neglect in childhood increases

the incidence of both anxiety and depressive disorders in

adult life

• the two disorders respond similarly to a variety of

therapeutic agents, including ssri antidepressants and

cognitive therapy

• the distribution of illness within families suggests that

the genetic diatheses underlying depressive and anxiety

disorders are very similar, and possibly identical in the case

of generalized anxiety disorder

Table 2

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ConCeptual and HistoriCal BaCkground

• DSM-IV mentions mixed anxiety–depressive disorder as only one of several ill-defined syndromes to be coded as ‘anxiety disorder not otherwise specified’.

• ICD-10 does rather better. It contains a category of mixed anxiety and depressive disorder (listed under the neurotic, stress-related and somatoform disorders) and also acknowl-edges that ‘individuals with this mixture of comparatively mild symptoms are frequently seen in primary care’, but even this does not do justice to the evidence.DSM-III attempted to deal with the problem of the co-occur-

rence of anxiety and depression by imposing a hierarchy which required that, if the criteria for major depression were met, anxi-ety syndromes were normally to be ignored. This hierarchy was largely abandoned in DSM-III-R (published in 1987) and DSM-IV, with the result that simple and social phobias, obsessive–compul-sive disorder and post-traumatic stress disorder were allowed to co-exist with major depression. The American National Comor-bidity Study and other community surveys then revealed that the extent of comorbidity was greater than anyone had suspected, particularly between anxiety and depressive disorders and addic-tion syndromes. Indeed, comorbidity emerged almost as the rule rather than the exception. There are other reasons, too, for sus-pecting that depressive and anxiety disorders are much more inti-mately related than contemporary classifications and textbooks suggest. Childhood abuse, sexual or physical, increases the risk of both types of disorder in adult life and they respond similarly to a variety of therapeutic agents, including selective serotonin reuptake inhibitors (SSRIs) and cognitive therapy. Even more fundamentally, family studies suggest that the genetic basis of generalized anxiety disorder is very similar, and possibly identi-cal, to that of major depression.

Tyrer has long argued for the recognition of a ‘general neu-rotic syndrome’ characterized by the simultaneous presence of several anxiety and depressive symptoms in the absence of major stress in people with dependent or inhibited personalities.5 He has also suggested that the co-occurrence of syndromes of anxiety and depression, which carries a worse prognosis than either syndrome on its own, should be formally recognized as cothymia. The arguments for doing so are strong, but in the pres-ent author’s view the problems posed for psychiatric nosologies by the epidemiological, therapeutic and genetic evidence sum-marized above are so fundamental that they are unlikely to be solved by this measure alone.

Diagnosis of mood disorders

Depression: in a psychiatric setting the diagnosis of depression rarely presents serious difficulties. The fact that the patient has already sought psychiatric help, or has at least been referred for a psychiatric opinion, creates an expectation of psychiatric disor-der and the syndrome is both common and familiar. Depression is most frequently missed, or disregarded, in the presence of: • more prominent anxiety symptoms (particularly panic

attacks) • alcohol dependence • chronic physical illness.

Comorbidity is extremely common in all three of these situ-ations and it is important to diagnose the depression because it often merits independent treatment. Patients with a presenting

psYCHiatrY 8:2 46

complaint of unexplained pain in the head, abdomen or chest, and who attribute their fatigue, despondency and insomnia to this pain, are sometimes said to have ‘masked’ depressions. It would probably be more honest, though, to refer to ‘missed’ depres-sions, because if the patients are asked the appropriate ques-tions they usually prove to have sufficiently extensive depressive symptoms to meet the formal criteria for major depression.

Mania: the diagnosis of mania is most commonly missed by doc-tors who do not appreciate that a manic patient’s mood may be irritable rather than elated, and that grandiosity is not invari-able. Characteristic features of mania, which are usually pain-fully apparent to the patient’s friends and relatives if not to his doctor, include:

• increased speech and energy • a decreased need for sleep • loss of normal social inhibitions and of sensitivity to other

people’s feelings.

Diagnosis in primary care

Depression is much harder to diagnose in a primary care set-ting, partly because of the serious time constraints, but mainly because the patient commonly presents with somatic complaints and the GP is often intent on detecting serious physical disease. The doctor’s sensitivity to, and interest in, emotional distress is crucial. Indeed, there is evidence that patients who recognize that their doctor is prepared to take an interest in emotional dis-tress are correspondingly more willing to admit to psychological symptoms. This subtle interaction between doctor and patient is part of the reason why GPs vary so much in the frequency with which they diagnose, and treat, depression.

In fact, depressive illnesses are among the commonest rea-sons for consultation in primary care: in a recent international study of 15 centres they accounted for over 10% of consecutive attenders. Depressions are also rewarding to treat, and apprecia-tion of these two facts is crucial to successful detection. Unex-plained somatic symptoms, new or increased anxiety symptoms and excessive alcohol intake should all raise the suspicion of an underlying or accompanying depression; if asked the appro-priate questions, few patients actively conceal their depressive symptoms. Loss of enjoyment of what were previously pleasures (anhedonia) and difficulty reading a newspaper or novel (impair-ment of concentration) are both valuable diagnostic clues. ◆

RefeRenCeS

1 kendell re. the classification of depressions: a review of

contemporary confusion. Br J Psychiatry 1976; 129: 15–28.

2 World Health organization. the iCd-10 classification of mental

and behavioural disorders: clinical descriptions and diagnostic

guidelines, geneva: WHo, 1992.

3 american psychiatric association. diagnostic and statistical manual

of mental disorders, 4th edn Washington, dC: apa, 1994 (dsM-iV).

4 parker g. Classifying depression: should paradigms lost be

regained? Am J Psychiatry 2000; 157: 1195–203.

5 tyrer p. Classification of neurosis, Chichester: Wiley, 1989.

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