Background Although visual hallucinations in Parkinson's disease (PD) have been described in several major studies, little is known about olfactory hallucinations (OHs).
Methods The authors performed a detailed analysis of OHs in a cohort of 87 Parkinsonian patients to estimate the prevalence of OHs and describe their phenomenology. They also evaluated smelling abilities in terms of detection and identification. Assessment of both, OHs and olfactory function, was also performed using a control group of 40 normal subjects.
Results Nine patients exhibited OHs compared with none of the controls, giving a prevalence of 10% for OHs in patients. OHs were described as rare, short-lasting, unpleasant odours which are not frightening since clearly identified by the patient as hallucinations. Parkinsonian patients with OHs exhibited olfactory impairment of detection and identification compared with controls, but there was no difference in their olfactory abilities from Parkinsonian patients without OHs.
Conclusions In conclusion, OHs should be added to the list of non-motor PD symptoms that can occur early or late in the course of PD. The authors' study did not reveal any significant difference in terms of olfactory abilities between patients with or without OHs. However, olfactory impairment is well documented in Parkinsonian patients and cannot be totally ruled out as a risk factor for OHs. The authors recognise that complex mechanisms are probably involved in this phenomenon.
- Parkinson's disease
- olfactory hallucinations
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Competing interests None.
Ethics approval Ethics approval was provided by the regional Medical School Ethics Committee (AU474).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Two posters were selected for the movement disorders congress, Chicago 2008; poster 1080: a new test to evaluate olfaction impairment by S Bannier et al. poster 1081: results of a new test detecting smell impairment in PD by S Bannier et al. One poster has also been selected for the movement disorders congress in Paris 2009: poster 378: olfactory hallucinations, prevalence and phenomenology in Parkinson's disease.