Visual hallucinations: Differentiating psychiatric and neurologic causes

Abstract

A visual hallucination is a visual percept experienced when awake that is not elicited by an external stimulus.Historically, hallucinations have been synonymous with psychiatric disease, most notably schizophrenia; however, over recent decades, hallucinations have been categorized based on their underlying etiology as psychodynamic (primary psychiatric), psychophysiologic (primary neurologic/ structural), and psychobiochemical (neurotransmitter dysfunction).1 Presently, visual hallucinations are known to be caused by a wide variety of primary psychiatric, neurologic, ophthalmologic, and chemicallymediated conditions.Despite these causes, clinically differentiating the characteristics and qualities of visual hallucinations is often a lesserknown skillset among clinicians.The utility of this skillset is important for the clinician's ability to differentiate the expected and unexpected characteristics of visual hallucinations in patients with both known and unknown neuropsychiatric conditions.Though many primary psychiatric and neurologic conditions have been associated with and/or known to cause visual hallucinations, this review focuses on the following grouped causes:• Primary psychiatric causes: psychiatric disorders with psychotic features and delirium; and• Primary neurologic causes: neurodegenerative disease/dementias, seizure disorders, migraine disorders, vision loss, peduncular hallucinosis, and hypnagogic/hypnopompic phenomena.