When it comes to our five senses, our ability to smell usually gets forgotten unless we come into contact with something especially unpleasant. However, new research suggests this underappreciated sense, or rather an impairment of it, could be used to help identify Parkinson’s disease in patients up to 10 years before symptoms, such as trembling and stiffness, develop.
In a study now published online in Neurology, researchers said they've designed a test that may help to measure someone's sense of smell, which could then lead to earlier diagnosis and treatment. In tests, they discovered the link between poor smell and Parkinson's was also greater in men, though they don't know why. Parkinson's is a neurodegenerative brain disease with no cure, and we're also not sure what causes it, according to the National Parkinson’s Foundation.
"Earlier studies had shown prediction of Parkinson's disease about four to five years after the smell test was taken," said study author Honglei Chen in a recent statement. "Our study shows that this test may be able to inform the risk much earlier than that."
For the research, the team looked at 2,462 people with an average age of 75 who took a scratch and sniff test where they were asked to identify common scents such as lemon, gasoline, onion, and cinnamon, Healthline reported. The volunteers were then followed for an average of 10 years.
Over the course of the decade, individuals who did poorly on the smell test were more likely to have developed Parkinson’s disease than those with a good or medium sense of smell. This correlation seemed to be strongest for white men when compared to black men. These results remained even after the team accounted for other factors that can increase risk, such as smoking, drinking coffee, and history of serious head injury.
Although there is no cure for the disease, there are a number of treatments that minimize symptoms, the most common of which include: trembling hands, arms, legs, face, and jaw; stiffness in the arms, legs, or body; slowed movement; and poor balance and coordination. There is also no lab test to diagnose the condition, and doctors don't usually spot it until symptoms appear. However, this can be several years after the disease has already begun to cause neurological damage, which can make treatment more difficult, Medline Plus reported.
The team emphasized that not everyone who scored low on the smell test went on to develop the disease. Still, the numbers were strong enough to suggest that the correlation was due to more than chance, and the researchers would like to further explore what may cause this connection.
Source: Chen H, Shrestha S, Huang X, et al. Olfaction and incident Parkinson disease in US white and black older adults. Neurology . 2017