Phantosmias and Parkinson disease

Area of Science:

• Neurology
• Neuroscience
• Ophthalmology

Background:

• Impaired olfaction is a recognized nonmotor symptom of Parkinson disease (PD).
• Qualitative olfactory disturbances, like odor distortions, are less commonly reported in PD.
• This study focuses on olfactory hallucinations (phantosmias) as a potential early indicator.

Observation:

• Two patients experienced pleasant olfactory hallucinations for years before developing typical PD symptoms.
• These phantasmic experiences occurred in the absence of significant smell deficits.
• The hallucinations ceased upon the onset of overt PD motor signs.

Findings:

• Iodine I 123-labeled ioflupane SPECT scans revealed reduced radiotracer uptake in the striatum, particularly the putamen, in both patients.
• Olfactometric testing indicated mild hyposmia in one patient and normal olfactory function in the other.
• The timing of phantosmia disappearance correlated with the emergence of PD motor symptoms.

Implications:

• Phantosmia is proposed as a novel premotor manifestation of Parkinson disease.
• Qualitative olfactory abnormalities, not just smell loss, should be investigated during the prodromal phase of PD.
• Identifying phantosmia could lead to earlier diagnosis and intervention for Parkinson disease.