Non-visual hallucinations in Parkinson’s disease: a systematic review

Abstract

Background Non-visual hallucinations in Parkinson’s disease (PD) can be prevalent and distressing. Most existing research has however, focused on visual hallucinations as well as related risk factors. The current study thus conducted a systematic review to collate existing evidence on non-visual hallucinations in PD, focusing on their prevalence, phenomenology, and clinical-cognitive correlates. Methods Ninety-one relevant studies were included from a systematic search across PsycINFO APA, PubMed, and Web of Science, for peer-reviewed publications in the English language, from 1970 to the present. These comprised a mix of case (30 studies; n = 56) and group design (62 studies; n = 7346) studies, divided into three somewhat overlapping collections to address our three research foci. Results Prevalence estimates for hallucinations were: auditory 1.5–72.0%, olfactory 1.6–21.0%, somatic-tactile 0.4–22.5%, gustatory 1.0–15.0%, and sensed presence 0.9–73.3%. Phenomenological inquiries revealed descriptions of vivid, consuming events replete with elaborate detail, adversely affecting PD patients in different ways. Overt experiences of multisensory hallucinations were also highly variable (0.4–80%) but exceedingly common, reported by almost half of the 45 included prevalence studies. There was some evidence for modality-specific hallucination predictors, but this was largely tentative, pending robust replication. Conclusions Marked prevalence figures coupled with phenomenological descriptions implicating distress denote that non-visual and multisensory hallucinations in PD are of clinical significance. More direct research and clinical attention need to be devoted to the study and management of such hallucinatory experiences.

Phantosmia in Parkinson’s Disease: A Systematic Review of the Phenomenology of Olfactory Hallucinations

“…OHs have been frequently studied in the context of psychiatric disorders or neurological conditions due to epilepsy or COVID-19 infection, while their features in PD are less understood [ 13 , 14 , 15 ]. Among non-visual hallucinations, OHs may frequently occur in PD patients, but they are often overlooked in clinical practice [ 47 ]. Moreover, clinicians should always check for phantosmia during the disease’s clinical course, not just at the baseline assessment, as longitudinal studies have identified phantosmia in initially unaffected PD patients [ 32 , 48 , 49 ].…”

Indicative biomarkers of Lewy body disease with oral sensory hallucinations in the older people

“…Oral sensory hallucinations (OSHs), referred to as oral cenesthopathy, are psychiatric symptoms predominantly observed in older individuals 1 . Nonvisual hallucinations, including OSHs, have been identified as clinical features that have potential to support the diagnosis of Parkinson's disease (PD) and dementia with Lewy bodies (DLB) 2,3 . Since individuals with PD/DLB have alterations in the dopaminergic system due to alpha‐synucleinopathy, 3,4 research suggests that OSHs may also be linked to these alterations 3–5 .…”

“… 1 Nonvisual hallucinations, including OSHs, have been identified as clinical features that have potential to support the diagnosis of Parkinson's disease (PD) and dementia with Lewy bodies (DLB). 2 , 3 Since individuals with PD/DLB have alterations in the dopaminergic system due to alpha‐synucleinopathy, 3 , 4 research suggests that OSHs may also be linked to these alterations. 3 , 4 , 5 However, the underlying pathophysiology of OSHs remains unclear.…”

Olfactory Dysfunction and Glaucoma

“…In PD, hyposmia is one of the first non-motor signs of the disease [28,30,31], and olfactory hallucinations (phantosmia) are reported in up to 21% of cases [32]. In addition, the olfactory threshold has been proposed as a test to differentiate Lewy bodies dementia (LBD) from Parkinson's dementia, as patients with LBD have a much lower olfactory threshold [33].…”