Smell Test in Screening for Parkinson's Disease Risk

Molecular model of polypeptide parkin

Identification of early or prodromal stages of the diseases of neuroscience medicine is an important clinical and research goal.

Identification of prodromal illness allows for enhanced surveillance and initiation of secondary prevention interventions.

Impairment of smell or olfactory sensation is a key early clue for Parkinson's disease (PD).

Danna Jennings and colleagues recently published an important study of the role of smell impairment in prodromal PD.

This manuscript represents one finding from the Parkinson's Associated Risk Syndrome Study.

In the published study, 4,999 subjects completed Tier 1 assessments of a multi-tier study. Subjects were recruited from 16 movement disorder clinics.

Tier 1 included olfactory testing and questionnaires. Tier 2 assessments include neurologic examination, brain imaging for dopamine transporter (DAT) function and other biomarker testing. 

The DAT is considered a valid marker of brain dopamine function and marker for prodromal PD.

Olfactory testing consisted of the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Subjects scoring in the lowest 15% of smell function were classified as abnormal or hyposmic.

The key findings from this study including the following points:

• Hyposmic subjects had higher rates of subjective smell impairment (47% versus 10% of controls)
• Hyposmic subjects did not have greater scores on current PD symptoms
• Hyposmic subjects had greater rates of DAT deficits on brain imaging (11% versus 1%)
• Combining hyposmia status along with male gender and presence of constipation identified a high-risk PD group where 40% had DAT deficit

A take home conclusion from the study is that elder men with constipation (< one bowel movement per day) and self-reported or UPSIT smell impairment have increased risk for PD.

Clinicians with more interest in smell testing kits can find information and purchase kits from Sensonics, Inc. The link for this test is here. Sensonics did not sponsor or provide financial incentive for this post.

Readers with more interest in this research can access the free full-text manuscript by clicking on the PMID link in the citation below. 

Follow the author on Twitter @WRY999

Figure in post is a molecular model of the crystal structure of the polypeptide parkin. Figure reproduced under terms of Creative Commons License. Figure published in Wikipedia is created by author JFtrempe. Parkin gene effects appear to contribute to risk for PD.

 Jennings D, Siderowf A, Stern M, Seibyl J, Eberly S, Oakes D, Marek K, & PARS Investigators (2014). Imaging prodromal Parkinson disease: the Parkinson Associated Risk Syndrome Study. Neurology, 83 (19), 1739-46 PMID: 25298306