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After reading this article, readers will be familiar with:
• The characteristic features of auditory hallucinations
• The assessment and differential diagnosis of auditory hallucinations
• The characteristics of auditory hallucinations that are typically indicative of psychosis
• Recent theoretical frameworks
• Various treatments
Throughout history, auditory hallucinations have been construed as evidence of communication with divine powers, although contemporary medical models often view them as undesirable and a sign of mental illness. In psychiatry, auditory hallucinations carry considerable weight in the diagnostic process, so there is a clear need for clinicians to have a greater understanding of the multiple facets of this phenomenon.
Auditory hallucinations are false perceptions of sound. They have been described as the experience of internal words or noises that have no real origin in the outside world and are perceived to be separate from the person’s mental processes.1 Auditory hallucinations have veridical perceptual qualities in the sense that individuals are often convinced of the objective reality of the experience. In most cases, auditory hallucinations are unintentional, intrusive, and unwanted. Affected individuals may or may not have insight into the hallucinations. A person with insight will acknowledge that the experience is abnormal and will report less interference with daily activities than a person with no insight.
This article provides an overview of the characteristic features of auditory hallucinations in psychiatric illness. The assessment and differential diagnosis of auditory hallucinations, recent theoretical frameworks, and treatment options are also briefly discussed.
Auditory hallucinations in diagnosis
Auditory hallucinations feature prominently in many psychiatric disorders. It has been estimated that approximately 75% of people with schizophrenia experience auditory hallucinations. These hallucinations are also relatively common in bipolar disorder (20% to 50%), in major depression with psychotic features (10%), and in posttraumatic stress disorder (40%).2
Not all auditory hallucinations are associated with mental illness, and studies show that 10% to 40% of people without a psychiatric illness report hallucinatory experiences in the auditory modality.3,4 A range of organic brain disorders is also associated with hallucinations, including temporal lobe epilepsy; delirium; dementia; focal brain lesions; neuroinfections, such as viral encephalitis; and cerebral tumors.5 Intoxication or withdrawal from substances such as alcohol, cocaine, and amphetamines is also associated with auditory hallucinations.
Hypnagogic and hypnopompic hallucinations are especially common in healthy individuals and occur during the period of falling asleep or waking up. The frequency of these experiences in the general population may be evidence of the existence of a symptomatic continuum, which ranges from subclinical experiences of psychosis to full-blown psychotic episodes with severe, unwanted, and intrusive symptoms.6
The phenomenological characteristics of auditory hallucinations differ on the basis of their etiology, and this can have diagnostic implications. People without mental illness tend to report a greater proportion of positive voices, a higher level of control over the voices, less frequent hallucinatory experiences, and less interference with activities than people who have a psychiatric illness.7,8
There is also evidence that delusion formation may distinguish psychotic disorders from nonclinical hallucinatory experiences.9 In other words, the development of delusions in people with auditory hallucinations significantly increases the risk of psychosis when compared with individuals who have hallucinations but not delusions.
By contrast, characteristics of auditory hallucinations that are thought to be more indicative of psychosis include8,10:
• Higher frequency of hallucinatory experiences
• Localization of voices outside the head
• Greater linguistic complexity
• Greater emotional response
• The extent to which patients believe that other people share this experience
Because of the multiple causes of auditory hallucinations, physicians must take care to obtain detailed histories from the patient, to assess for mood and psychotic symptoms, and to obtain collateral information. Laboratory tests and brain scans can also offer further clues to the underlying cause of the hallucinations.
Clinical assessment of auditory hallucinations
Patients are usually able to describe their hallucinatory experiences. The Schedules for Clinical Assessment in Neuropsychiatry1 provides a standard question that can be used in assessing symptoms: “Do you ever seem to hear noises or voices when there is nobody about, and no ordinary explanation seems possible?” A description of the experience in the patient’s own words is required for a positive rating.
Patients will often underreport their hallucinatory experiences because of the possible implications of further treatment action. Collateral information can be helpful, as is repeated interviewing. True auditory hallucinations must be differentiated from:
• Auditory illusions (misinterpretations of real existing stimuli)
• Vivid auditory imagery (under volitional control)
• Abnormal beliefs (such as a delusion of reference, when individuals report that other people are talking about them)
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