Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fears and anxieties. Current psychiatric diagnostic criteria recognize a wide variety of anxiety disorders. Recent surveys have found that as many as 18% of Americans may be affected by one or more of them.

Diagnosis

Anxiety disorders are often debilitating chronic conditions, which can be present from an early age or begin suddenly after a triggering event. They are prone to flare up at times of high stress and are frequently accompanied by physiological symptoms such as headache, sweating, muscle spasms, palpitations, and hypertension, which in some cases lead to fatigue or even exhaustion.

Although in casual discourse the words anxiety and fear are often used interchangeably, in clinical usage, they have distinct meanings; anxiety is defined as an unpleasant emotional state for which the cause is either not readily identified or perceived to be uncontrollable or unavoidable, whereas fear is an emotional and physiological response to a recognized external threat. The term anxiety disorder, however, includes fears as well as anxieties. Indeed, phobias (fears which are "persistent or irrational") constitute the majority of anxiety disorder cases.

Anxiety disorders are often comorbid with other mental disorders, particularly clinical depression. Studies have also indicated that anxiety disorders are more likely among those with family history of anxiety disorders, especially certain types.

Causes and contributing factors

Clinical and animal studies suggest a correlation between anxiety disorders and difficulty in maintaining balance. A possible mechanism is malfunction in the parabrachial nucleus, a brain structure that, among other functions, coordinates signals from the amygdala with input concerning balance. The amygdala is involved in the emotion of fear.

Especially the basolateral amygdala has been implicated in anxiety generation. A relationship between anxiety and dendritic arborization of the amygdaloid neurons is well known. SK2 potassium channels mediate inhibitory influence on action potentials and reduce arborization. By overexpressing SK2 in the basolateral amygdala, anxiety was reduced and stress-induced corticosterone secretion at a systemic level decreased in an animal model. Mutations in related SK3 are suspected to be a possible underlying cause for several neurological disorders, including anxiety.Fact: date=April 2009

Additionally, low levels of GABA, a neurotransmitter that reduces activity in the central nervous system, contribute to anxiety. A number of anxiolytics achieve their effect by modulating the GABA receptors.