Hallucination is a sensory perception in the absence of corresponding external stimuli, occurring while the patient is awake. Hallucinations can affect any sensory modality and may indicate psychiatric disorders, neurological conditions, or substance-related states.

• Auditory hallucinations: Perception of nonexistent sounds, usually voices; common in schizophrenia.

• Olfactory hallucinations: Perception of nonexistent odors; often linked to temporal lobe lesions or somatic delusions.

• Tactile hallucinations: Perception of nonexistent touch or movement on/under the skin; common in toxic states and substance abuse (e.g., alcohol withdrawal).

• Visual hallucinations: Perception of nonexistent images, people, or lights; often associated with organic brain disorders.

• Gustatory hallucinations: Perception of nonexistent tastes, usually unpleasant.

Pathophysiology

• Hallucinations arise from abnormal activation of sensory pathways or cortical areas without external input.

• Auditory hallucinations: Hyperactivity in the temporal and auditory cortices, often linked to dopaminergic dysregulation.

• Visual hallucinations: Dysfunction in the occipital cortex or visual association areas, sometimes due to metabolic or structural brain disorders.

• Olfactory/tactile/gustatory hallucinations: Localized cortical or limbic system disturbances.

• Substance-induced: Neurotransmitter imbalances (dopamine, serotonin, acetylcholine) alter perception.

Examination Technique

1. Patient interview: Ask about perceived sensations, onset, frequency, and triggers.

2. Sensory modality identification: Determine auditory, visual, tactile, olfactory, or gustatory.

3. Reality testing: Assess whether the patient recognizes the hallucination as unreal (insight).

4. Associated features: Evaluate mood, thought content, orientation, and cognitive function.

5. Documentation: Record type, frequency, duration, triggers, and insight level.

Clinical Features

Differential Diagnosis

Pediatric considerations

• Hallucinations are rare in children; assess for trauma, fever, or neurodevelopmental disorders.

• Children may describe imaginary friends or objects, which requires careful differentiation from normal imagination.

Geriatric considerations

• Older adults may experience visual hallucinations due to dementia, delirium, or sensory impairment.

• Insight may be impaired, increasing the risk of distress or behavioral problems.

Limitations

• Patients may underreport hallucinations due to fear of stigma.

• Differentiating hallucinations from illusions or vivid imagination may be challenging.

• Requires integration with history, mental status, and neurological examination.

Patient counseling

• Explain that hallucinations are perceptions without external stimuli and are symptoms of an underlying condition.

• Encourage reporting frequency, triggers, and distress caused.

• Reassure that effective treatments exist, including medications and psychotherapy.

• Emphasize safety if hallucinations lead to risky behavior.

Conclusion

Hallucinations are abnormal sensory experiences that may indicate psychiatric, neurological, or substance-related conditions. Careful assessment of type, insight, and associated features guides diagnosis, monitoring, and treatment.

References

1. Berrios GE. Hallucinations: Conceptual models and clinical implications. Schizophr Bull. 2000;26(3):523–538.

2. Sadock BJ, Sadock VA, Ruiz P. Kaplan & Sadock’s Comprehensive Textbook of Psychiatry. 10th ed. Philadelphia: Wolters Kluwer; 2021.

3. American Psychiatric Association. DSM-5 Diagnostic Criteria for Hallucinations. 2013.

4. Tandon R, et al. Psychotic disorders and hallucinations: Assessment and management. Lancet Psychiatry. 2016;3:447–459.