Anxiety disorders are very common. Approximately 40 million US adults aged 18 years and older, or about 18.1% of people in this age group in a given year, have an anxiety disorder. They frequently co-occur with depressive disorders or substance abuse, and most people with one anxiety disorder also have another anxiety disorder. Nearly three-quarters of those with an anxiety disorder will have their first episode by age 21.

Anxiety disorders have several possible etiologies and there are a number of theories, from the biologic to the psychodynamic, that contribute to our understanding. They are discussed in very general terms below.

The fear network is thought to be influenced by genetic factors and stressful life events, particularly events in early childhood. Genetic variants of several candidate genes of neurotransmitter or neurohormonal systems, each with a small individual effect, may contribute to the susceptibility to anxiety and mood disorders. The biologic vulnerability to certain anxiety disorders varies from person to person. This vulnerability may never be stressed, however, and a person with the same family history may not develop the disorder. Brain chemistry and developmental factors also play a role. Studies have shown that variations in the autonomic nervous system or noradrenergic system may cause some people to experience anxiety to a greater degree than others. Other studies suggest abnormalities in the regulation of substances such as serotonin and gamma-aminobutyric acid (GABA) may play a role in the development of anxiety disorders.

Fear and anxiety are also influenced and mediated by several interacting brain structures, such as the amygdala, hippocampus, striatum and locus coeruleus, which may play a role in making individuals more vulnerable to an anxiety disorder.

Psychological factors appear to play a part in the development of anxiety disorders. Long-term exposure to abuse, violence, or poverty may affect a person’s susceptibility. According to learning theory, anxiety may result from conditioning, by which a person develops an anxious response by linking a dangerous or fear-inducing event (e.g., a house fire) with a neutral event (e.g., watching someone light a match). In cases of general anxiety, a person may learn the anxiety response when he or she begins to liken any anxious symptoms with a full-fledged anxiety attack, causing a vicious anxiety cycle to continue.

Cognitive theories explain anxiety as a manifestation of distorted thinking and suggest that the individual’s perception or attitude overestimates the danger of the stimulus that evokes their anxiety response. According to cognitive theorists, many people with anxiety disorders have a tendency to catastrophically misinterpret autonomic arousal sensations that occur in the context of no pathological anxiety.

There is a great deal of overlap between the symptoms of anxiety disorders and major depression, although the core symptoms (worry, anxiety and fear versus depressed mood) differ. Overlapping symptoms include problems with sleep, concentration, fatigue, and psychomotor/arousal symptoms. From a diagnostic standpoint, it might make little difference whether a patient has anxiety or depression insofar as pharmacologic treatments are similar.

The essential features of panic disorder are recurrent, unexpected panic attacks that cause the affected person to persistently worry about recurrences or complications from the attacks or to undergo behavioral changes in response to the attacks for at least 1 month. Panic disorder may be with or without agoraphobia.

Panic attacks typically are characterized by a discrete period of intense apprehension or terror without any real accompanying danger. The clinical picture involves a physiologic and psychologic over-response to stressors. A person experiencing a panic attack may perceive the circumstances to be life-threatening and experience such reactions as chest pain, choking or smothering sensations, dizziness, dyspnea, fainting, hot and cold flashes, palpitations, paresthesias, sweating, and vertigo. The person may also report feelings of depersonalization or derealization, feelings of dread or doom, fears of dying or losing their mind, or fears of engaging in some sort of uncontrollable behaviors. Attacks typically last for several minutes, reaching a peak within 10 minutes.

Panic attacks are frightening and uncomfortable and people may make extreme efforts to escape from what they believe to be causing the panic and their behavior may appear strange or erratic to others. Between panic attacks, the person often remains moderately to severely anxious in anticipation of the next episode.

Although panic attacks are unpredictable in onset, they may occur in specific situations, such as driving an automobile, but not necessarily every time the patient engages in the activity. Panic attacks may occur in other circumstances and this feature is helpful in distinguishing panic attacks from phobias.

Panic disorder can occur with agoraphobia, which is a marked fear of being alone or in a public place from which escape would be difficult or help would be unavailable in the event of becoming disabled. Recent data suggest that the prevalence of lifetime comorbidity in panic disorder with agoraphobia is 100%. Agoraphobia is the most severe and persistent phobic disorder. People with agoraphobia often fear such scenarios as being outside the house alone, using public or mass transportation, and being in a crowd. As a response, many people with agoraphobia avoid such situations or endure them with such agony that they rearrange their lifestyles to minimize these occurrences (e.g., restrict their travel, stop leaving the house). Eventually, the limitations that agoraphobia imposes may diminish the person’s enjoyment of life and lead to depression.

This/these disorders are highly comorbid with other anxiety disorders, major depression, somatoform disorders, pain-related disorders, substance-abuse disorders, and personality disorders. Panic disorder symptoms may wax and wane but, if left untreated, the typical course is chronic. In general, among those receiving tertiary treatment, approximately 30% of patients have symptoms that are in remission, 40–50% are improved but still have significant symptoms, and 20–30% are unimproved or worse at 6- to 10-year follow-up.

Treatment goals as they pertain to panic disorder with and without agoraphobia are, in general, to reduce the frequency and severity of panic attacks, avoidance behaviors, and panic-related disability in social and occupational functioning. There are a number of approaches that can be taken in treating panic disorder with and without agoraphobia. Interventions with the most enduring treatment effects include cognitive–behavioral therapy and particular pharmacotherapies (e.g., a selective serotonin-reuptake inhibitor, imipramine, clomipramine). Serotonin/norepinephrine-reuptake inhibitors are another promising treatment. High-potency benzodiazepines are effective in the short term but are less effective in producing long-term remission of panic disorder.

Obsessive–compulsive disorder (OCD) is an often debilitating syndrome characterized by the presence of two distinct phenomena: obsessions and compulsions. Obsessions are intrusive, recurrent, unwanted ideas, thoughts, or impulses that are difficult to dismiss despite their disturbing nature. Compulsions are repetitive behaviors, either observable or mental, that are intended to reduce the anxiety engendered by obsessions. Obsessions or compulsions that clearly interfere with functioning and/or cause significant distress are the hallmark of OCD.

Most affected patients have multiple obsessions and compulsions over time, with a particular fear or concern dominating the clinical picture at any one time. The presence of obsessions without compulsions, or compulsions without obsessions, is unusual.

The disorder is characterized of common obsessions. Contamination obsessions are the most frequently encountered, usually characterized by a fear of dirt or germs. Contamination fears may also involve toxins or environmental hazards (e.g., asbestos or lead) or bodily waste or secretions. Excessive washing is the compulsion most commonly associated with contamination obsessions.

The need for symmetry describes a drive to order or arrange things perfectly or to perform certain behaviors symmetrically or in a balanced way. Patients describe an urge to repeat motor acts until they achieve a “just right” feeling that the act has been completed perfectly. Patients with a prominent need for symmetry may have little anxiety but rather describe feeling unsettled or uneasy if they cannot repeat actions or order things to their satisfaction. Patients with a need for symmetry frequently present with obsessional slowness, taking hours to perform acts such as grooming or brushing their teeth.

Patients with somatic obsessions are worried about the possibility that they have or will contract an illness or disease.

People with sexual or aggressive obsessions are plagued by fears that they might harm others or commit a sexually unacceptable act such as molestation. Often, they are fearful not only that they will commit a dreadful act in the future but also that they have already committed the act. Patients are usually horrified by the content of their obsessions and are reluctant to divulge them. Patients with these highly distressing obsessions frequently have checking and confession or reassurance rituals.

Pathological doubt is a common feature of patients with OCD who have a variety of different obsessions and compulsions. Individuals with pathological doubt are plagued by the concern that, as a result of their carelessness, they will be responsible for a dire event.

Comorbidity includes major depression, and OCD is highly comorbid with the other anxiety disorders. Although findings have varied, the generally accepted frequency of tic disorders in patients with OCD is far higher than in the general population, with a rate of approximately 5–10% for Tourette’s disorder and 20% for any tic disorder. Conversely, patients with Tourette’s disorder have a high rate of comorbid OCD, with 30–40% reporting obsessive–compulsive symptoms. Finally, it has long been noted that the co-occurrence of OCD symptoms in patients with psychotic disorders is more than would be expected by chance.

Age at onset usually refers to the age when OCD symptoms (obsessions and compulsions) reach a severity level wherein they lead to impaired functioning or significant distress or are time-consuming (i.e., meet DSM-IV-TR criteria for the disorder). Reported age at onset is usually during late adolescence.

Earlier age at onset has been associated with an increased rate of OCD in first-degree relatives. These data suggest that there is a familial type of OCD characterized by early onset. Age at onset of OCD may also be a predictor of course. The vast majority of patients report a gradual worsening of obsessions and compulsions prior to the onset of full-criteria OCD, which is followed by a chronic course. A subtype of OCD that begins before puberty has been described in the literature. It is characterized by an episodic course with intense exacerbations. Exacerbations of OCD symptoms in this subtype have been linked with group A beta-hemolytic streptococcal infections, which has led to the subtype designation of pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). In a study of 50 children with PANDAS, the average age of onset was 7.4 years.

In terms of prognosis, a recent meta-analysis pooled 16 study samples comprising 521 children followed for between 1 and 15.6 years. The persistence of OCD was lower than previously believed. The authors reported that two-thirds of studies showed that OCD did not persist as a full clinical syndrome in the majority of subjects. The pooled mean rate of persistence of full-threshold OCD was 41%. The persistence of OCD was predicted by inpatient treatment, longer duration of illness at baseline, and an earlier age at onset of OCD. However, gender, age at assessment, and length of follow-up may also be related to the persistence of OCD.