Classification of depression

If there are different types of depression then they may have different causes and outcomes, and respond to different treatments

The classification of depression (what types of depression exist) is a controversial topic that has caused much debate between psychiatrists. This debate matters because if there are different types of depression then they may have different causes and outcomes, and respond to different treatments.

Dispute arises because diagnoses are simply based on the presence of certain, arbitrarily defined, symptoms.

There's still no diagnostic test for depression, such as a blood test or scan, which is able to confirm whether somebody has the illness.

This lack of an objective 'gold standard' diagnosis means that doctors do not know for certain whether the clusters of symptoms they use for diagnosis are valid, or even if they are dealing with one or more than one diseases that have the same central symptom of low mood.

Historically different psychiatrists previously used different criteria to diagnose depression. Much of the resulting confusion has been curtailed by the advent of internationally recognised sets of diagnostic criteria, such as the Diagnostic and Statistical Manual (DSM) and the International Classification of Disease (ICD).

These criteria have led to a greater uniformity of approach to the diagnosis and classification of depressive illnesses. However, the criteria and classes of depression are constantly updated with each new version of DSM and ICD, and there continues to be differences in opinion between some psychiatrists.

Previously held views of the different types of depression

Over the years, various authorities have attempted to subdivide 'straight forward' depression (excluding illnesses such as postnatal depression and seasonal affective disorder) on the basis of the cause of the illness and the type of symptoms experienced.

Proposed sub-divisions include:

  • endogenous versus reactive depression
  • psychotic versus neurotic depression
  • major versus minor depression.

    Endogenous versus reactive depression

    The endogenous versus reactive classification was based on ideas regarding the cause of the depressive illness.

    Endogenous depression
    • 'Endogenous' (occurs from within) implies there is no discernible cause for the depression.
    • It was believed that this type of depression is more likely to be passed on to children due to a larger genetic component than reactive depression.
    • This form of depression was thought to be characterised by a high proportion of biological symptoms (sleep and appetite disturbance, poor concentration and memory, loss of interest in sex).
    • Some authorities thought this form of depression was most likely to respond to antidepressant treatments.
      Reactive depression
      • 'Reactive' implies that the depression results from some stress occurring in the sufferer's life.
      • The risk of this type of depression occurring was believed to have more to do with the severity of life stresses than inherited factors.
      • Symptoms were thought to be typified by worry and anxiety, with problems getting to sleep rather than waking early in the morning (as in endogenous depression).
      • It was originally argued that patients with reactive depression were less likely to respond to antidepressants.

        Psychotic versus neurotic depression

        This differentiation centred on the premise that patients with depression could be divided into two groups on the basis of their symptoms.

        This classification almost exactly matched the endogenous versus reactive classification, with the 'psychotic' group being similar to the 'endogenous' group.

        The use of the term 'psychotic' is extremely confusing, since it normally refers to the presence of particular symptoms (hallucinations and delusions) that were not necessarily present in 'psychotic depression' as defined in this classification.

        Major versus minor depression

        The terms major and minor depression should not be used.

        The use of the term 'minor' is not only derogatory, but it also encouraged a lack of treatment of patients with so-called 'minor depression'.

        The term 'major' is also confusing, since it does not necessarily imply 'severe' illness.

        Reasons why these types are no longer accepted

        • Patients with endogenous depression are as likely to have suffered a stressful event before the start of their illness as those with reactive depression.
        • Reactive depression is as likely to be inherited as endogenous depression.
        • Patients cannot be separated into different categories on the basis of symptoms: patients with biological symptoms are also highly likely to be anxious.
        • Reactive depression responds to antidepressants equally as well as endogenous depression.

          Despite these more recent views and findings, it's still believed that:

          • for any individual there may be varying degrees of inherited risk to depression and severity of life stresses that brought about the illness. It is important to consider both social and environmental factors and genetics when trying to understand why a particular person develops depression at a particular point in time. These factors can influence treatment, but only to a limited extent. For example, if a person develops depression due to lots of stresses, it would be appropriate to help them address these. It would also be appropriate to treat the depression with medication or a talking therapy.
          • different people do have different symptoms, some with more biological symptoms, and some with more symptoms of anxiety. Both sorts of illness respond to antidepressants, although there is evidence that supports the use of certain types of antidepressants for depression with marked anxiety symptoms, eg a selective serotonin reuptake inhibitors (SSRI).

            Currently accepted types of depression

            Primary versus secondary depression

            This distinction is based on the proposed cause of the depressive illness in an individual.

            • Primary: the depression is not as a result of any other medical or psychological cause.
            • Secondary: the depression has been caused by a medical condition (eg a disorder of the thyroid gland) or psychiatric illness (eg schizophrenia).

              There is little evidence that these 'types' of depression are really different.

              However, this classification helps to draw attention to any possible underlying causes of the depression. These causes then need treating in their own right if the depression is to improve.

              Unipolar versus bipolar depression

              This classification is based on the course of the illness that an individual experiences.

              • If a patient has only ever had episodes of depression, they are described as having a unipolar affective disorder (recurrent depressive illness).
              • If a patient has had at least one episode of elevated mood (mania) as well as episodes of depression, they are described as suffering from a bipolar affective disorder (manic depression). A few people only experience episodes of mania. They are also referred to as suffering from bipolar affective disorder.

                The unipolar versus bipolar distinction is important because a number of differences between the two illnesses exist.

                • Both disorders can be inherited, but this is more likely to be the case with bipolar disorder. The children of unipolar disorder parents have an increased risk of this type of depression. However, the children of people with bipolar disorder have an increased risk of both, which suggests the two disorders are related.
                • Bipolar disorder tends to begin earlier in life than unipolar disorder, often starting in the early 20s rather than in the 30 to 40 year age range.
                • Patients with bipolar disorder tend to have more frequent episodes of illness than patients with unipolar depression, though these episodes tend to be shorter.
                • Bipolar disorder can sometimes be made worse by antidepressants, which can precipitate a manic (elevated mood) episode and lead to more frequent episodes of illness. Mood stabilisers, such as lithium, and some anticonvulsants are the mainstay of treatment for bipolar disorder patients.

                  Depressive illness versus depressive symptoms

                  Everybody may experience low mood from time to time, but this is different from suffering from a depressive illness.

                  A depressive illness is diagnosed when a person has a number of depressive symptoms consistently over a couple of weeks or more.

                  According to the diagnostic criteria of DSM and ICD, a depressive illness is present if a person is suffering from a certain number of specified symptoms.

                  However, there are some people who experience several depressive symptoms, but not enough such symptoms to fulfil the diagnostic criteria for a depressive illness?

                  In these situations there are a number of possibilities:

                  • the person may not be suffering from a depressive illness
                  • the person may be suffering from a depressive illness that has a slightly different pattern of symptoms, which doesn't fit with the arbitrarily defined list of symptoms defined in the criteria
                  • the person may be suffering from a milder form of depressive illness
                  • the person may be in the early stages of a depressive illness and over time develop more symptoms and hence fulfil the diagnostic criteria.

                    These possibilities affect the way that a person with depressive symptoms, but not fulfilling criteria for a depressive illness, gets treated:

                    • if symptoms have been present for less than two weeks, beyond giving some general support and possibly counselling, antidepressants tend not to be used
                    • however, if the symptoms are severe and have been present for more than two weeks, a doctor would be more likely to prescribe antidepressants
                    • the progress of people with depressive symptoms should be monitored, since they may go on to develop a full-blown depressive illness that will clearly require treatment.

                      Dysthymia (chronic mild depression) versus depressive illness

                      This distinction is based on the severity and number of symptoms, and the duration of the illness.

                      Dysthymia is defined by the presence of depressive symptoms for at least two years.

                      A diagnosis of dysthymia rather than a depressive illness is made because:

                      • either there are not enough symptoms present to fulfil the diagnostic criteria for a depressive illness
                      • or the symptoms are not present for the majority of time but may come and go for a few days at a time.

                        Dysthymia appears to respond differently to treatment in comparison to depressive illnesses.

                        • There is less evidence that counselling or psychotherapies work.
                        • Antidepressants may be of some help, but they can take months (rather than two to four weeks) to start working. As a result, a great deal of patience is called for on both the part of the patient and the doctor.

                          People with dysthymia are at increased risk of also developing a full-blown depressive illness on top of their ongoing depressive symptoms.

                          This is sometimes called 'double depression', meaning dysthymia plus a depressive illness. If this happens, then treatment for the depressive illness is especially important to prevent a chronic full-blown depressive illness developing.

                          How would a consultant psychiatrist classify an episode of depression?

                          A psychiatrist would make a decision about a number of questions.

                          Have a sufficient number of symptoms been present for long enough to diagnose a depressive illness?

                          If this is not the case, the psychiatrist may recommend support from a counsellor and advise that the person should be reviewed to check if a more severe depression develops.

                          If there are insufficient symptoms to diagnose a depressive illness, have the symptoms been present for two years or more?

                          If they have, the diagnosis is of dysthmia, and this may lead the psychiatrist to recommend a trial of antidepressants, bearing in mind that they may take several months to act.

                          Is the illness primary or secondary?

                          If it is secondary, the illness that is causing the depression will need to be treated.

                          Is the illness part of a bipolar disorder?

                          If it is, the psychiatrist may be less likely to prescribe antidepressants and may consider recommending mood stabilisers.

                          Has the illness been caused, or is it being maintained, by severe stress?

                          If this is the case, the causes of the stress need to be addressed, perhaps with the help of a social worker.

                          Does the patient have suicidal plans?

                          If the person does, it will be important for the psychiatrist to try to ensure they remain safe. This may be achieved by involving a friend or relative, or having a community psychiatric nurse (CPN) see the patient.

                          It's also possible that the psychiatrist may recommend the person should come into hospital for a period of time – though this is far from inevitable.

                          Does the patient have psychotic symptoms?

                          Psychotic symptoms are hallucinations (such as hearing or seeing something that is not there) and delusions (false beliefs that the person holds unshakeably).

                          If these symptoms are present, an antipsychotic medication in addition to antidepressants is likely to be needed.

                          Does the patient have prominent anxiety symptoms?

                          If anxiety symptoms are present, these may influence the type of antidepressant that's recommended to the patient.

                          Antidepressants that influence the serotonin (5-HT) system in the brain seem to be best, such as the selective serotonin reuptake inhibitors (SSRIs).

                          Based on a text by Dr Hamish McAllister-Williams, MRC clinical scientist, senior lecturer and honorary consultant psychiatrist

                          Last updated

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