Early observations of melancholia (the most severe form of depression) suggested that it could have physical or psychological origins and that depression and mania could occur at different times in the same person. Although theories about the underlying causes of depression changed over the centuries, there was a remarkable level of consistency in the descriptions of the core symptoms with sadness and despondency accompanied by sleep problems and physical complaints. However, mental illness remained a broad concept in the 18th and 19th centuries and whilst evidence of ‘madness’ frequently led to admission to an asylum, there were only rudimentary attempts to differentiate between or classify mental disorders.
The turn of the 20th century saw huge changes. There was a realization that severe mental illnesses (increasingly referred to as psychosis) were not uniform and that this ‘loss of reason’ might take different forms. Also, less severe but disabling forms of mental disorder (sometimes called neuroses) were described and there was a move towards providing private outpatient treatments for many of these individuals. To give an insight into these developments and how they influenced current thinking on depression, we briefly review the contributions of Emil Kraepelin and Sigmund Freud. The ideas expressed by these two individuals have moved in and out of fashion over the last century. We include these descriptions because, whether current experts, clinicians, or readers of this text agree or disagree with the views put forward by Kraepelin or Freud, it is clear that their theories have cast a long shadow over our understanding of depression and its treatment.
Emil Kraepelin was, and remains, one of the most influential figures in psychiatry. He was born in 1856 in Neustrelitz in north Germany. After qualifying in medicine he trained in psychiatry in Munich where the emphasis was to find a physical cause of mental illness through studying the brain. Kraepelin was also interested in other approaches and models, and he worked in Leipzig with Wilhelm Wundt, a well-known psychologist. Kraepelin worked as an asylum psychiatrist, became a professor, and then moved to Heidelberg where he began his now famous meticulous studies of asylum patients. He kept written cards on each patient noting their symptoms and the course and outcome of their illness and then wrote a series of textbooks (entitled Psychiatrie) where he described his observations of clinical cases and emerging ideas on how to categorize mental conditions. Kraepelin highlighted that the causes of psychiatric illnesses were largely not understood, and that the same mental symptoms could occur in more than one disorder, but he suggested that the course and outcome of the clinical presentation could be used to distinguish between subgroups of patients with different diagnoses. In 1899, Kraepelin described the identification of two distinct types of ‘functional’ (non-organic) psychotic illness: Manic Depressive Insanity and Dementia Praecox (which we now know as schizophrenia).
In Kraepelin’s classification, Dementia Praecox included all psychotic illnesses without an overt mood component, and these patients showed gradual continuous decline without any periods of recovery; Kraepelin believed that this presentation eventually progressed to dementia. In contrast, those with Manic Depressive Insanity usually (but not always) demonstrated changes in mood, cognition, and behaviour (referred to as motor activity). Also, these changes followed an intermittent and recurrent course, with periods of recovery between episodes. He stated that the term Manic Depressive Insanity described a number of related mood disorders and that ‘as its name indicates, it takes its course in single attacks, which either present the signs of so called manic excitement (flight of ideas, exaltation and over-activity), or those of a peculiar psychic depression with psychomotor inhibition, or a mixture of the two states’.
Kraepelin regarded melancholia as part of the spectrum of Manic Depressive Insanity and noted that the treatment of the former often overlapped with the treatment of the latter. He also believed that his classification system would ultimately be validated by medical research that would identify the underlying causes of the illnesses.
The recognition of the two conditions (Dementia Praecox and Manic Depressive Insanity) was not entirely new, but Kraepelin offered the clearest and most decisive descriptions. Nevertheless, his proposed classification was not universally accepted, and even today there is considerable debate about how he categorized certain mood disorders or personality problems, including conditions such as chronic depression. Kraepelin’s attempts to develop a more systematic framework for defining different patterns of illness and disease progression still influence modern classification systems for mental disorders to this day, although the term manic depressive illness has largely been replaced by the term bipolar disorder (see Box 2).
Kraepelin classified all mood disorders as part of the spectrum of manic depressive insanity.
Over time, an alternative model began to be accepted which hypothesized that there were two distinct categories of mood disorder: one where patients experience episodes of mania and depression and another where depression only is experienced. In 1957 Karl Leonhard, a German psychiatrist, is credited with coining the term ‘bipolar’ to describe the condition of episodic mania and depression and ‘unipolar’ for illness characterized by depression only. These terms may have been used by his predecessor Karl Kleist; a German psychiatrist with whom Leonhard worked.
This distinction between unipolar and bipolar disorders was further validated in 1966 by Perris and Angst who found that the two conditions could be distinguished by differences in family history of the disorder. In the 1960s, the term bipolar disorder was used for the first time to replace manic depression in the published diagnostic manuals.
Sigmund Freud was born in 1856 in Freiburg, a small town in Moravia. He was the eldest of eight children and it is said that he was his mother’s favourite. Indeed, many texts on the early life of Freud make much of the fact that his mother called him ‘my golden Sigi’. The family moved to Vienna when Freud was young and he remained there until 1938 when he moved to London to escape the persecution of Jews at the outbreak of the Second World War.
Freud became interested in neurology when he was a medical student and in 1885 he went to study with the famous neurologist Jean-Martin Charcot at the Salpêtrière Institute in Paris. Charcot had an interest in hysteria, which was described as a neurotic condition because physical symptoms experienced by the patient such as paralysis did not have a clear physical (organic) basis. Charcot used hypnosis to demonstrate that the patient’s clinical presentation was associated with ongoing conflicts that could explain the symptoms experienced, and argued that the patient’s psychological distress had been transformed or ‘converted’ into a physical problem. Charcot proposed that the use of hypnotic suggestion could release these unconscious forces and bring about improvement.
Freud realized that the unconscious mind had a very powerful effect upon behaviour, and extended the use of hypnosis to uncover unconscious memories of traumas which the person was not aware of and had repressed. Through a series of detailed case studies, Freud developed theories to explain how unresolved conflicts from the past could produce specific neurotic symptoms and illness later in life. He then proposed that psychoanalysis could help resolve these conflicts and create a healthier mental state.
Freud’s concepts of depression can be traced to his three hypothetical models of how the mind (or psyche as he called it) is organized, how personality develops, and the possible causes of neurotic illness. These models are reviewed very briefly to give a flavour of the ideas expressed, but interested readers may wish to consult other texts to examine these ideas in detail. In his first theory, called the topography of the mind, Freud suggested that the mind had three parts: the conscious, the preconscious (things we are not currently attending to, but that we can access and focus on), and the unconscious (which we are unaware of, but which can exert influence upon us).
Freud also described a structural model of how personality shapes our actions and reactions, a theory that is sometimes called the second topography. This is important because it introduced the concepts of the id, ego, and superego. In Freud’s view, the id is driven by the pleasure principle, namely a need for the immediate gratification of its desires and functions in the unconscious. The ego strives to satisfy the id in appropriate ways, operating as an intermediary between the id and the outside world. The ego is associated with the reality principle, for example allowing delayed gratification of the id to occur in a socially acceptable manner and at an appropriate moment in time. Freud proposed a range of defence mechanisms that were used to maintain equilibrium including, for example, rationalizing the reasons for acting in a certain way or being in denial about the consequences of an impulsive behaviour. The superego is the final element of personality that develops (around the age of 5 years) and it provides a sense of right and wrong and modifies the actions of the ego. For healthy personality development Freud suggested that the id, the ego, and the superego have to be in balance. He believed that any imbalance would lead to the development of a neurosis such as depression or anxiety. For example, Freud suggested that if the drives of the id override the superego, guilt is experienced, or if the ego suppresses the id, anxiety occurs.
Freud’s third theory of the mind concerned childhood sexual development and the stages that an infant has to pass through successfully to become a healthy adult. The theory divides human development into a predictable sequence such as the oral, anal, and phallic stages (associated with the Oedipus complex), etc. Freud believed conflict in any of the stages explained both the later development of neurosis and the type of symptoms experienced. He also proposed certain personality traits were associated with failure to pass through a specific stage of development. For example, Freud proposed that difficulties in the anal stage were related to the development of obsessional symptoms. In contrast, difficulties in the oral stage were manifest in adult life by personality traits such as passivity, dependency, and self-doubt which he suggested were common in people prone to developing depression.
In 1917, Freud published a famous work entitled Mourning and Melancholia in which he compared melancholia (severe depression) with mourning (the grief experienced by someone following a bereavement). He described both conditions as being associated with loss but suggested that the difference was in the feelings associated with the different types of loss. In mourning the loss was recognized at a conscious level—the person who has died was the ‘lost object’ and the feelings associated with the bereavement such as sadness and anger were expressed outwardly. In contrast, Freud proposed that in melancholia the loss was of an ‘ideal object’, for example the loss of love (e.g. experienced after rejection or the breakdown of a relationship). Furthermore, he suggested that, unlike mourning, the loss was partly unconscious in melancholia and anger towards the lost object was redirected against the self. In addition, Freud stated that a person who reacts to loss by developing melancholia has either reverted to, or never moved on from, an earlier stage of development. He stated that those who are likely to become depressed have an impaired sense of self-worth so when the ‘object’ is lost they have nothing to fall back on of themselves and this lack of resilience increases the risk that they will become depressed.
Freud differentiated depression from other neuroses on the basis of symptoms and the hypothesized development origins. Nowadays, many of his ideas have been discarded or revised, but his work helped to illuminate the continuum from ‘normal sadness’ to depression and how personality characteristics and illness symptoms can overlap. However, Freud’s models arose from work undertaken mainly with upper- or middle-class women in a private outpatient clinic in Vienna—a very different population from the asylum cases observed by Kraepelin that informed the categorization of psychoses. Nevertheless, the ideas of both men influenced later attempts to define the boundaries of depression and approaches to diagnosis and classification of mental disorders.
One of the problems encountered in any discussion of depression is that the word is used to mean different things by different people. For many members of the public, the term depression is used to describe normal sadness. In clinical practice, the term depression can be used to describe negative mood states, which are symptoms that can occur in a range of illnesses (e.g. individuals with psychosis may also report depressed mood). However, the term depression can also be used to refer to a diagnosis. When employed in this way it is meant to indicate that a cluster of symptoms have all occurred together, with the most common changes being in mood, thoughts, feelings, and behaviours. Theoretically, all these symptoms need to be present to make a diagnosis of depressive disorder.
The word diagnosis originates from Greek, from ‘dia’ apart and ‘gignokein’ to recognize or know. In any medical speciality, the first step in making a diagnosis is an assessment interview. In branches of medicine other than psychiatry a range of investigations can be used to aid the process of diagnosis. For example, a suspected diagnosis of ischaemic heart disease can be confirmed by performing an angiogram (a test in which a special dye is injected into the blood vessels that can make visible any narrowing of the arteries supplying blood to the heart muscles). The absence of any laboratory tests in psychiatry means that the diagnosis of depression relies on clinical judgement and the recognition of patterns of symptoms. There are two main problems with this. First, the diagnosis represents an attempt to impose a ‘present/absent’ or ‘yes/no’ classification on a problem that, in reality, is dimensional and varies in duration and severity. Also, many symptoms are likely to show some degree of overlap with pre-existing personality traits. Taken together, this means there is an ongoing concern about the point at which depression or depressive symptoms should be regarded as a mental disorder, that is, where to situate the dividing line on a continuum from health to normal sadness to illness. Second, for many years, there was a lack of consistent agreement on what combination of symptoms and impaired functioning would benefit from clinical intervention. This lack of consensus on the threshold for treatment, or for deciding which treatment to use, is a major source of problems to this day.
Such issues have undermined research in mood disorders, clinical practice, and also public confidence in the concept of depression and rationale for its treatment. Over a number of decades, there have been international efforts to standardize approaches to diagnosis through the introduction of criterion-based classifications of mental disorders. Box 3 gives an example of the criteria used for the diagnosis of major depression according to the Diagnostic and Statistical Manual of Mental Disorders (IVth Edition) of the American Psychiatric Association (this set of criteria is not the most recent, but was chosen as they are easier to digest than some of the others). The process of applying these criteria goes through several steps. For example, if it is determined that the symptoms a person reports can be categorized as a depressive disorder, a dimensional rating of the intensity of the symptoms is then made to clarify if the depression should be regarded as mild, moderate, or severe. Other steps are also possible. For example, it is possible to specify additional features of the presentation such as whether the depression is accompanied by any loss of reality (psychotic depression), etc.
A careful inspection of the criteria for identifying a depressive disorder demonstrates that diagnosis is mainly reliant on the cross-sectional assessment of the way the person presents at that moment in time. It is also emphasized that the current presentation should represent a change from the person’s usual state, as this step helps to begin the process of differentiating illness episodes from long-standing personality traits. Clarifying the longitudinal history of any lifetime problems can help also to establish, for example, whether the person has previously experienced mania (in which case their diagnosis will be revised to bipolar disorder), or whether they have a history of chronic depression, with persistent symptoms that may be less severe but are nevertheless very debilitating (this is usually called dysthymia). In addition, it is important to assess whether the person has another mental or physical disorder as well as these may frequently co-occur with depression.
The classification systems introduced for mental disorders were initially developed separately in America (Diagnostic and Statistical Manual of Mental Disorders or DSM) and Europe (International Classification of Diseases or ICD). However, attempts have been made with the most recent revisions of these classification systems to more closely match the diagnostic approaches, to improve international consistency, and ensure groups are communicating about and comparing the same problem. In the absence of diagnostic tests, the current classifications still rely on expert consensus regarding symptom profiles.
The classification system is not static and the range of presentations of depression that are recognized and their location within the classification manuals has changed over time. For example, in the early editions of DSM (which were influenced by Freud’s models of depression), persistent but milder depressive symptoms (referred to as dysthymia) were regarded primarily as a personality type and so they were located within that category in the textbook on classification. Later revisions of DSM were based less on unproven theoretical models, and tried to make decisions about classification based on empirical evidence. Several research studies indicated there were many overlaps between major depressive and dysthymic symptoms, and that 80 per cent of individuals with dysthymia experience a major depression at some point in their life. As such, it was argued that dysthymia should be reclassified as a type of mood disorder.
Moving the location of a condition within a classification system may seem like an academic or intellectual exercise, but it is important to recognize that such shifts can have significant implications as one of the roles of diagnosis and classification is to guide treatment decisions. The relocation of dysthymia meant that the treatments offered shifted from psychotherapy only (an intervention recommended to address difficulties experienced as a consequence of certain personality traits) to options that included both therapy and medications (as used for many mood disorders). However, this simple example exposes the weaknesses of the current system. Even if changes to the classification system can be justified on the basis of new scientific findings, they are potentially open to biases and so it is all too obvious why it provokes scepticism in some quarters.
In summary, for a classification system to have utility it needs to be reliable and valid. If a diagnosis is reliable doctors will all make the same diagnosis when they interview patients who present with the same set of symptoms. If a diagnosis has predictive validity it means that it is possible to forecast the future course of the illness in individuals with the same diagnosis and to anticipate their likely response to different treatments. For many decades, the lack of reliability so undermined the credibility of psychiatric diagnoses that most of the revisions of the classification systems between the 1950s and 2010 focused on improving diagnostic reliability. However, insufficient attention has been given to validity and until this is improved, the criteria used for diagnosing depressive disorders will continue to be regarded as somewhat arbitrary (e.g. there is little empirical evidence to support the use of a cut-off of the presence of a minimum five out of nine symptoms persisting for two weeks for diagnosing a depression as a major episode).
Weaknesses in the systems for the diagnosis and classification of depression are frequently raised in discussions about the existence of depression as a separate entity and concerns about the rationale for treatment. It is notable that general medicine uses a similar approach to making decisions regarding the health–illness dimension. For example, levels of blood pressure exist on a continuum. However, when an individual’s blood pressure measurement reaches a predefined level, it is reported that the person now meets the criteria specified for the diagnosis of hypertension (high blood pressure). Depending on the degree of variation from the norm or average values for their age and gender, the person will be offered different interventions. They may be asked to attend regular monitoring sessions and to modify their lifestyle. However, if the problem persists or is regarded as more severe, a range of other interventions and treatment with medications may be suggested. This approach is widely accepted as a rational approach to managing this common physical health problem, yet a similar ‘stepped care’ approach to depression is often derided. This exposes the frequent double standards that seem to operate for common physical health as compared to mental health problems, where the same approach to clinical management is regarded as unscientific or controversial for depression.
It is worth noting that, in the absence of objective laboratory tests, the current approach to the diagnosis of depression does have the benefit of pragmatism. It can be argued that when the severity, duration, degree of distress, and level of social impairment associated with a set of symptoms reach an agreed threshold then the problem warrants clinical attention and the individual deserves help to cope with these experiences.