Evidence-Based Reviews

Hallucinations: Common features and causes

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Awareness of manifestations, nonpsychiatric etiologies can help pinpoint a diagnosis



Not all patients who experience hallucinations have a psychotic disorder. Many physical and psychiatric disorders can manifest with hallucinations, and some patients have >1 disorder that could cause different types of hallucinations. To avoid providing unnecessary or ineffective treatments—and to ensure that patients receive proper care for nonpsychiatric conditions—it is important to accurately diagnose the disorder causing a patient’s hallucinations.

In this article we describe common features and psychiatric and nonpsychiatric causes of auditory, visual, olfactory, gustatory, tactile, and somatic hallucinations. Awareness of typical presentations of hallucinations associated with specific disorders can help narrow the diagnosis and provide appropriate treatment.

Auditory hallucinations

Also known as paracusia, auditory hallucinations are perceptions of sounds without identifiable external stimuli. This type of hallucination has various causes (Table 1).1 A frequent symptom of schizophrenia, auditory hallucinations can cause substantial distress and functional disability.2 Approximately 60% to 90% of patients with schizophrenia and up to 80% of those with affective psychoses experience auditory hallucinations.1

Auditory hallucinations in psychosis usually are formed and complex.3 A common manifestation is hearing ≥1 voices. A patient might experience 2 voices talking about him in the third person. The voices may be perceived as coming from inside or outside the patient’s head. Some might hear their own thoughts spoken aloud. According to DSM-IV-TR, “hearing voices” is sufficient to diagnose schizophrenia if the hallucinations consist of a voice keeping up a running commentary on the person’s behavior or ≥2 voices conversing with each other.4 Auditory hallucinations also are seen in mood disorders but tend to be milder than their psychosis-induced counterparts.

Simple (unformed) auditory hallucinations—referred to as tinnitus—can be caused by disease of the middle ear (otosclerosis) or inner ear. These unformed hallucinations consist of buzzing or tones of varying pitch and timbre.1

Partial seizures may cause auditory hallucinations. Perceptions of music have been associated with partial seizures.5 Curie and colleagues found that 17% of 514 patients with temporal lobe epilepsy had auditory hallucinations as a component of their seizures.6 These hallucinations typically are brief, stereotyped sensory impressions and, if formed, may be trivial sentences, previously heard phrases, or commands.

Alcoholic hallucinosis is a hallucinatory syndrome caused by alcohol withdrawal. These hallucinations usually are vocal and typically consist of accusatory, threatening, and/or critical voices directed at the patient.1 Patients with alcohol hallucinosis also may experience musical auditory hallucinations.7,8

CNS neoplasms can produce auditory hallucinations in 3% to 10% of patients.9 Hemorrhages and arteriovenous malformations in the pontine tegmentum and lower midbrain have been associated with acute onset of auditory hallucinations. The sounds typically are unformed mechanical or seashell-like noises or music.10

Patients with migraines rarely report auditory hallucinations. When they occur, they typically consist of perceived unilateral tinnitus, phonophobia, or hearing loss.

Table 1

Common causes of auditory hallucinations

Peripheral lesions
Middle ear disease
Inner ear disease
Auditory nerve disease
CNS disorders
Temporal lobe epilepsy
Pontine lesions
Arteriovenous malformations
Toxic metabolic disturbances
Alcoholic hallucinosis
Psychotic depression
Dissociative identity disorder
Posttraumatic stress disorder
Source: Reference 1

Visual hallucinations

Visual hallucinations manifest as visual sensory perceptions in the absence of external stimuli.11 These false perceptions may consist of formed images (eg, people) or unformed images (eg, flashes of light).12 Visual hallucinations occur in numerous ophthalmologic, neurologic, medical, and psychiatric disorders (Table 2).13

DSM-IV-TR lists visual hallucinations as a primary diagnostic criterion for several psychotic disorders, including schizophrenia and schizoaffective disorder,4 and they occur in 16% to 72% of patients with these conditions.14,15 Patients with major depressive disorder or bipolar disorder also may experience visual hallucinations. Visual hallucinations in those with schizophrenia tend to involve vivid scenes with family members, religious figures, and/or animals.16

Delirium is a transient, reversible cause of cerebral dysfunction that often presents with hallucinations. Several studies have shown that visual hallucinations are the most common type among patients with delirium. Webster and Holroyd found visual hallucinations in 27% of 227 delirium patients.17

Delirium tremens typically is accompanied by visual hallucinations. Visions of small animals and crawling insects are common.18 Hallucinations due to drug intoxication or withdrawal generally vary in duration from brief to continuous; such experiences often contribute to agitation.19

Migraines are a well-recognized cause of visual hallucinations. Up to 31% of those with migraines experience an aura, and nearly 99% of those with aura have visual symptoms.20,21 The classic visual aura starts as an irregular colored crescent of light with multi-colored edges in the center of the visual field that gradually progresses toward the periphery, lasting <60 minutes. These simple visual hallucinations are most common; more complex hallucinations are seen more frequently in migraine coma and familial hemiplegic migraine.


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