To assess the prevalence of Olfactory Hallucinations (OlfH) in patients presenting to a tertiary movement disorders outpatient clinic.

Hallucinations are a non-motor feature of alpha synucleinopathies and occur in 20-50% of patients with PD. Due to a lack of awareness as well as paucity of structured questionnaires/tests that target psychosis assessment with an emphasis on olfactory hallucinations (OlfH), these are often missed during clinical consultations.

Singe site, cross-sectional (ongoing, total n = 200), IRB approved study. Patients diagnosed with Parkinson’s disease per UK brain bank criteria by a movement disorder specialist were consecutively enrolled with their informed consent and completed a questionnaire and self-administered a University of Pennsylvania Smell Identification Test (UPSIT). Inability to understand the instructions due to language barrier or severe underlying pathology were exclusion criteria. 

Of the 130 patients who completed the study so far, 36% were women and 64% men. Mean age was 66.3 ± 9.6 year. Approximately 18% of the patients (28) had a prior olfactory assessment. 23 (17.7%) patients endorsed olfactory hallucinations, of which 15 (65%) were men. Hallucinations in other sensory modalities were also reported: Visual (15.3%), Auditory (8.46%) and Tactile (6.9%). In the patients with OlfH (n=23); concurrent sensory hallucinations included visual (30.4%), auditory (17.3%) and tactile (13%). 2 patients reported hallucinations in all four modalities. 43% of patients with OlfH had a poor sense of smell objectively (UPSIT showed severe microsmia or anosmia). The most commonly described hallucinations were “smoke/cigarette smoke”. While most reported that OlfH were infrequent, 18% (n=2) reported hallucinations lasting >1 hour and found them unpleasant and upsetting.

Non-motor symptoms of PD are often missed in routine clinical practice and have far-reaching implications in patient care. OlfH tend to be underreported with prevalence ranging from 2.1% to 10% in prior studies compared to 17.7% in our cohort.