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What is anxiety?
Anxiety is a normal physiological response to stress which is designed to alert us to dangers in our immediate environment. Anxiety disorders differ from nonpathological anxiety as they are characterized by excessive feelings of fear which impact on a person’s daily functioning.
Often, people with an anxiety disorder will actively avoid the fear-provoking situation or stimulus, leading to disruption to work or school performance or social functioning.
Although there are many different forms of anxiety disorder including social anxiety, specific phobia, obsessive-compulsive disorder and generalized anxiety disorder, each with a specific set of diagnostic criteria, all share the following core components:
- Anxiety that is either disproportionate to the situation or stimulus, or age inappropriate,
- Sufficiently severe to hinder functioning in some way.
Anxiety disorders are the commonest form of mental illness, with a lifetime prevalence of approximately 33% within the general population. Both anxiety disorder and depression are clinically common mental disorders.
What is depression?
Depression is a common mood disorder characterised by low mood, feelings of sadness and a loss of interest in everyday activities that persists over time and impacts daily functioning.
Although common, it is a serious medical illness which can affect how people think and act and can decrease a person’s ability to function emotionally, physically, socially and occupationally. Symptoms of depression can range from mild to severe and often include:
- Feelings of sadness or irritability,
- Loss of interest in once pleasurable activities,
- Changes to sleep patterns
- Changes to appetite or weight
- Change in activity level, characterized either by psychomotor agitation or retardation
- Loss of energy
- Impaired ability to concentrate or make decisions
- Feelings of guilt or worthlessness
- Thoughts of suicide or self-harm.
Although most people will not experience all these symptoms, at least five must be present for most of each day for at least two weeks to receive a diagnosis of depression.
The co-occurrence of depression and anxiety disorders
Studies of the general population show that depression and anxiety commonly co-occur, whilst rates of co-morbidity in clinical samples are even higher.
In a study of over one thousand individuals receiving outpatient treatment for anxiety disorders, 57% had at least one current co-morbid disorder, most commonly a mood disorder.
In a similar study of 1,004 primary mental health care patients with an anxiety disorder, over two-thirds also met the diagnostic criteria for depression.
Same or different?
Given that depression and anxiety are strongly linked, and share similar etiologies, risk factors and genetic markers, some researchers have considered whether they are different manifestations of a single underlying process.
One study supporting this hypothesis use a survey of 313 outpatients with various anxiety disorders and depression.
Using principal components analysis, a statistical technique used to detect strong patterns in data, it identified a core pathological process linking anxiety and depression.
Processes that are shared by numerous psychological disorders are referred to as transdiagnostic and have important implications for treatment. Transdiagnostic treatment models are more efficient to train and deliver than multiple diagnostic specific models, whilst retaining therapeutic efficacy.
However, such an approach may conflate the association between symptoms by over-simplifying their relationship and obscuring key differences.
For example, more advanced and modern statistical techniques such as network analysis demonstrate that symptoms of depression are arranged in a ‘dynamic architecture’; changes in the severity of one symptom lead to other symptoms changing in the same direction, a finding they termed ‘symptom spread’.
Furthermore, certain symptoms caused greater spread than others did.
This effect is referred to as the causal symptoms perspective and has contributed greatly to the understanding of psychiatric co-morbidity over the past decade.
Network analysis of data from over one thousand patients admitted to psychiatric inpatient care, modelled symptoms of anxiety and depression to investigate the strength of symptom associations between the two disorders.
Individual symptoms of depression and anxiety were more strongly associated with other symptoms within each disorder than to symptoms between disorders. This suggests that depression and anxiety are similar, yet distinct disorders.
Work is ongoing to better understand the relationship between depression and anxiety.
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