New, Easier Smell Test May Better Detect Parkinson’s at Early Stages

A rapid, inexpensive, and easy-to-use test can help to assess a loss of smell, and with greater accuracy than current “scratch and sniff” tests, allowing neurological disorders like Parkinson’s disease to be suspected at early stages, researchers report.

Their study “A novel capsule-based smell test fabricated via coaxial dripping” was published in The Journal of Royal Society Interface.

Loss of smell is an early symptom of chronic neurodegenerative diseases, including Alzheimer’s and, especially, Parkinson’s disease. In fact, evidence indicates that up to 90% of Parkinson’s patients experience a loss of smell, the study noted.

“Early detection of neurodegenerative diseases is important under the assumption that those at the earliest stages will be more likely to gain benefit from neuroprotective clinical trials and future treatments,” the researchers wrote.

“Scratch-and-sniff” tests are frequently used to determine a person’s sense of smell, where tiny beads of scented oils are encapsulated on an adhesive material, such as paper, that release scented oils as they burst upon being scratched.

However, these types of tests are expensive — a single test can cost almost $27, researchers noted — so to be ill-suited to large screening programs, and their accuracy could vary from person to person.

“The problem with this [scratch-and-sniff] approach is that the amount of odor released depends on the extent to which the individual scratches, something that might affect the outcome of the test,” Ahmed Ismail, PhD, with Queen Mary’s School of Engineering and Materials Science in London, and the study’s lead author, said in a press release.

“Our capsule-based smell test doesn’t have this problem because the amount of odor released is controlled by the amount of oil precisely encapsulated. The mass-production of our new test would also be cheaper,” Ismail added.

Researchers developed a test that uses alginate, a natural hydrogel derived from seaweed, to encapsulate a drop of scented oil, with the capsule placed between two strips of single-sided tape. (Alginate is widely used to encapsulate products that include oils, drugs, dyes and vitamins.)

This method provides a controlled release of smell, achieved by crushing the capsule between the fingers and then peeling off a layer of tape to reach oil’s scent.

Researchers assessed their test’s effectiveness in a group of eight Parkinson’s patients. Participants performed two smell function tests, one using the conventional scratch method and the other using the alginate hydrogel capsule. In both cases, six odors were tested: menthol, coconut, onion, clove, orange, and cherry.

After each test, patients were asked to describe what they smelled and which test they preferred.

Patients were able to rupture all capsules (a total of 48), releasing the odor. On both series of tests, clove and onion were the most identifiable smells.

Out of the eight participants, five said they preferred the novel capsule smell test to the conventional scratch-and-sniff test. One of the main reasons, particularly for patients with tremors, was that the capsules were relatively easy to rupture compared to scratching.

This test “can assist in the rapid diagnostic of various diseases linked to the loss of smell,” which addition to chronic neurological ills like Parkinson’s and Alzheimers includes people with COVID-19.

The team noted, however, that more research is required and results “may vary depending on whether a test is screening for COVID-19, neurological conditions or another cause of hyposmia [poorer sense of smell], as the extent of olfactory dysfunction may differ with each condition.”