The potential utility of smell testing to screen for neurodegenerative disorders

ABSTRACT

Introduction

Loss of smell is a common early feature of neurodegenerative diseases including Alzheimer’s and Parkinson’s disease. Identifying these conditions in their early stages is important to understand more about early pathophysiological events and the development of disease modifying therapies. Smell testing may be an effective future tool for screening large populations for early neurodegeneration.

Areas Covered

In this review, we appraise the evidence for, and discuss the likelihood of, the use of smell testing in large screening programs to detect early neurodegeneration. We evaluate the predictive power of smell tests for neurodegenerative disease, compare performance to other established screening programs, and discuss ethical and practical considerations and limitations.

Expert Opinion

Even if disease modifying therapies were available for neurodegenerative disease, smell tests alone are unlikely to have high enough predictive power to be used in a future screening program. However, we believe they could be a valuable component of a short battery of tests or part of a stepwise process that together could more accurately identify early neurodegeneration in large populations.

KEYWORDS:

• Screening
• neurodegeneration
• smell
• Alzheimer’s disease
• Parkinson’s disease

Declaration of Interest

AJ Noyce reports grants from the Barts Charity, Parkinson’s UK, Cure Parkinson’s, Aligning Science Across Parkinson’s, Michael J Fox Foundation, and Alchemab. AJ Noyce reports consultancy and personal fees from Astra Zeneca, AbbVie, Alchemab, uMed, Profile, Roche, Biogen, UCB, Bial, Charco Neurotech and Britannia, outside the submitted work. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Article highlights

• Olfactory deficit is associated with, and may predict conversion to, neurodegenerative conditions such as Alzheimer’s and Parkinson’s disease.

• Early diagnosis of neurodegenerative diseases may be key to the development of disease limiting treatments for these conditions.

• Screening for diseases has been successful in other settings. A short smell test could act as an early screen to identify those at higher risk of neurodegenerative diseases or in the earlier stages.

• Smell tests could be used as a screening tool prior to the use of more accurate tests that are more specific to neurodegenerative conditions.

• The predictive accuracy of smell testing may be improved by combining it with other tests that can be performed cheaply and easily in the community, in a so-called test ‘battery.’

• However, mass screening or early detection away from a research setting depends on there being demonstrable benefit from this activity, such as disease modifying treatment or improvement in quality of life.

Additional information

Funding

The Preventive Neurology Unit is funded by the Barts Charity.