Types of Hallucinations
Hallucinations can occur in different sensory modalities, including visual, auditory, tactile, gustatory, and olfactory, and may present as either simple or complex experiences involving one or multiple senses. 1, 2
Hallucinations by Sensory Modality
Visual hallucinations: Perceptions of images without corresponding external stimuli, ranging from simple (lights, geometric figures) to complex (objects, people). These are particularly common in Parkinson's disease and Dementia with Lewy Bodies, occurring in up to 80% of patients. 3, 4
Auditory hallucinations: The most prevalent type of hallucination in schizophrenia, associated with earlier age of first hospitalization among schizophrenic patients. 5
Tactile hallucinations: Sensations of touch without external stimuli, often correlated with olfactory/gustatory hallucinations and severity of delusions in schizophrenic and schizoaffective patients. 5
Gustatory hallucinations: Taste perceptions without corresponding stimuli, less common than visual or auditory hallucinations. 6
Olfactory hallucinations: Smell perceptions without corresponding stimuli, often correlated with tactile hallucinations in psychiatric disorders. 5
Classification by Complexity
Simple hallucinations: Basic sensory experiences such as lights, colors, geometric patterns, simple sounds, or basic tactile sensations. 4
Complex hallucinations: More elaborate perceptions such as formed objects, people, voices, conversations, or complex scenes. 4
Multimodal hallucinations (MMHs): Hallucinations occurring in multiple sensory systems either simultaneously or serially in time. These are more prevalent than previously thought and may have greater adverse impact than unimodal hallucinations. 2
Specific Types of Visual Hallucinations
Peduncular hallucinations: Distinguished from Charles Bonnet Syndrome, which is characterized by visual hallucinations with preserved insight and vision loss. 7
Charles Bonnet Syndrome: Visual hallucinations occurring in patients with vision loss and preserved insight, without other neurological explanations. 3, 4
Visual illusions: Distinct from hallucinations, these involve misinterpretation of actual sensory input rather than perception without stimulus. Types include metamorphopsias, micro-macropsias, polyopia, palinopsia, achromatopsia, and Pulfrich phenomenon. 1, 4
Clinical Significance
Visual hallucinations in Parkinson's disease predict dementia, rapid deterioration, permanent nursing home placement, and death. 6
Visual hallucinations in Alzheimer's disease are often associated with serious behavioral problems and predict rapid cognitive decline. 6
Global severity of schizophrenia is related to the presence of visual hallucinations, but not other types of hallucinations. 5
Assessment Tools
Neuropsychiatric Inventory (NPI): A structured caregiver interview designed to detect and quantify neuropsychiatric symptom changes in people with dementia. 8
North-East Visual Hallucination Interview (NEVHI): Specifically assesses visual hallucinations with both patient and informant versions, showing strong correlation with MDS-UPDRS hallucination scores. 8, 3
University of Miami Parkinson's disease Hallucinations Questionnaire: Captures both severity and frequency of visual hallucinations. 8, 3
Scale for the Assessment of Positive Symptoms for Parkinson's Disease Psychosis (SAPS-PD): Evaluates multiple modalities of hallucinations and other psychotic elements. 8
Understanding the type and characteristics of hallucinations is crucial for accurate diagnosis, localization of neurological issues, and appropriate treatment planning. 6