Next Lesson - Psychosis
Core
This article will focus on disorders of mood, including depression, mania, hypomania, and bipolar disorder.
Depression is a condition of low mood that affects 5% of adults worldwide (source).
For a diagnosis of depression there must be at least 2 of the core symptoms of depression present for 2 or more weeks, usually alongside additional psychological or physical symptoms. There are 3 core symptoms of depression namely:
- Low mood
- Lack of energy
- Lack of enjoyment or interest in things the patient would usually enjoy (also known as anhedonia)
Depression is also associated with a number of ‘biological’ or ‘somatic’ symptoms:
- Reduced sleep or insomnia, usually characterised by early morning waking
- Hypersomnia - increased sleep
- Reduced appetite
- Psychomotor retardation
- Reduced libido (sex drive)
Unfortunately, the precise causes of most mental illnesses have not been identified at this time. However, a collection of risk factors has been identified, and if multiple are present simultaneously, this can increase the risk of mental illness. These can be categorised into predisposing factors (things the patient cannot change), perpetuating or maintaining factors (things in the patient’s life now that encourage mental illness), and precipitating factors (an event that ‘pushes’ the patient into mental illness).
Predisposing Factors:
- Genetics - a family history of depression makes it more likely
- Childhood experiences - abuse, loss of a parent, bullying
Perpetuating Factors:
- Stressful job or unemployment
- Financial strain
- Substance misuse
- Relationship difficulties
- Housing uncertainty
Precipitating Factors:
- Life events often related to loss - death of a loved one, end of a relationship, declining physical health
Adjustment Reactions vs Depression
It is important to differentiate between a normal response to a distressing event and clinical depression, especially because the traumatic event may be the precipitating factor for depression AND result in a normal adjustment reaction.
An adjustment reaction follows a traumatic event, with fluctuating symptoms including feelings of anger and frustration. There are no particular disturbances to sleep, appetite or energy levels.
Clinical depression is a condition of low mood, lack of energy and lack of enjoyment that comes on more gradually and must last for a period of 2 weeks or more. Lack of sleep (insomnia), poor appetite and lack of libido are common.
If an adjustment reaction persists and there are symptoms of depression present the reaction may have triggered the development of depression.
The table below describes the symptoms of both, to show the differences between these two conditions.
Table - The differences between adjustment reaction and clinical depression
There are many physical illnesses that can present similarly to depression, and it is therefore important to investigate for and treat these before diagnosing a patient with depression:
- Hormone disturbances such as thyroid dysfunction
- Deficiency of vitamins such as vitamin B12
- Kidney disease
- Alcohol and drug misuse
Mania and hypomania are conditions which both involve elevated mood. Mania must be present for at least 1 week (or any duration if hospitalisation is required), whereas hypomania must be present for at least 4 days. About 16 in 1000 people will experience mania at some point in their life (source).
Other than elevated mood symptoms include:
- Increased energy
- Pressure of speech (fast rate of speech)
- Reduced sleep
- Flight of ideas - a thought disorder in which thoughts change topic very quickly
- Loss of social inhibitions
- Inflated or grandiose self-esteem
Hypomania is considered to be a less severe version of mania. The main differentiating features are that mania causes marked functional impairment and may include psychotic symptoms such as hallucinations or delusions, whereas hypomania does not cause severe impairment and does not include psychotic symptoms.
Bipolar disorder is a diagnosis that can be made following two distinct episodes of a mood disturbance, at least one of which must be mania or hypomania.
This means that one episode of mania/hypomania and one of depression, or two episodes of mania/hypomania can both be characterised as bipolar disorder.
Bipolar disorder is relatively common in the UK, with 1 in 100 people being diagnosed with bipolar disorder at some point throughout their life (source).
Sometimes bipolar is classified into Bipolar 1 and 2 but this classification is debated. For reference:
- Bipolar 1 - Episodes of mania
- Bipolar 2 - Episodes of hypomania only, no episodes of mania
Structures Involved in Mood Disorders
There are three main structures in the brain that are thought to be involved in mood disorders.
The first system is the limbic system, a collection of structures that sits close to the corpus callosum in the centre of the brain. The main functions of the limbic system are the management of emotion, motivation and memory, and it is therefore thought to play a particular role in anxiety disorders. For more information on the limbic system, please see our article on Anxiety and Anxiety Disorders.
There is some debate around which structures should be included in the limbic system, but the most common components are:
- Amygdala
- Hippocampus
- Cingulate Gyrus
- Fornix
- Hypothalamus
- Thalamus
The frontal lobe has many different functions, including executive function, personality, attention, memory and mood. It is also connected to the limbic system. The frontal lobe impacts a large number of psychiatric conditions. For more information on the frontal lobe and its functions, please see our article on Topography of the Nervous System.
The basal ganglia are a group of structures found deep within the brain; these structures are closely related to the limbic system, and there is some crossover with structures being classified in both systems.
Its functions can be broadly categorised into motor functions and psychological functions (involving emotion, cognition and mood). Dysfunction of the basal ganglia can therefore lead to movement disorders such as Parkinson’s Disease or Huntington’s Disease (for more information, please see our article on Movement Disorders), or psychological disorders such as mood disorders.
Neurotransmitters are vital for the brain’s function, and chemical imbalances in the levels of neurotransmitters can be a contributor to mood disorders.
Noradrenaline has effects on the brain related to mood, behaviour and memory functions. It is produced in the locus coeruleus in the brainstem and transported into the cortex.
Serotonin has effects on the brain related to sleep, impulse control, appetite and mood. It is produced in the raphe nuclei of the brainstem, and is transported to the cortex and the limbic system.
Dopamine is particularly active in the basal ganglia, and therefore has effects related to motor function and mood, especially in the pathways relating to reward.
There are other neurotransmitters that are involved in mood disorders, such as Acetylcholine, GABA and Glutamate, but their effects are beyond the scope of this article.
See our article on neurotransmitters for more information.
The two main neurotransmitter abnormalities which are thought to contribute to depressive disorders are low serotonin and low noradrenaline. This is why two of the main classes of drugs used in depression, selective serotonin reuptake inhibitors (SSRIs) and serotonin noradrenaline reuptake inhibitors (SNRIs), are used in an attempt to increase the levels of these neurotransmitters.
One neurotransmitter abnormality found in manic disorders is high dopamine - this is why typical antipsychotics like haloperidol are dopamine receptor antagonists, meaning the high levels of dopamine do not trigger the receptors as much.
Another abnormality that may be found alongside dopaminergic changes is altered serotonergic signalling. This is why second-generation antipsychotics (also called atypical antipsychotics) act as dopamine and serotonin receptor antagonists. These drugs reduce the effects of excessive dopaminergic activity and modulate serotonin pathways.
There is also a class of drug called mood stabilisers, which includes lithium. These drugs are very effective in bipolar disorder to prevent severe episodes of mania or depression, and try to stabilise the mood.
The most important thing to consider when prescribing to patients with bipolar disorder is that giving antidepressants can induce a manic episode. For this reason, antidepressants are used with caution in bipolar disorder, usually alongside a mood stabiliser or antipsychotic, and with careful monitoring. Antidepressant monotherapy should be avoided in patients with a history of manic episodes or a diagnosis of bipolar disorder.
Edited by: Dr. Ben Appleby
Reviewed by: Dr. Thomas Burnell
In this article
Depression is a disorder of low mood, anhedonia, and lack of enjoyment, possibly with biological symptoms.
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