Here’s the list, but read on for the rest of the story.
Runners up are: dill pickle, wintergreen, mint, gasoline, smoke, cinnamon, aniseed, apple, lemon, and rose.
Current therapies for Parkinson’s disease treat only some of the symptoms of the disease. They do not treat the disease itself, and there is currently no convincing evidence that early detection and early treatment changes the disease progression. However, early detection has a few existing and future benefits:
- Early detection may help researchers understand more about how the disease progresses, where it starts and how it spreads.
- It would allow patients to identify their premotor symptoms for what they are, and seek quicker relief of those symptoms.
- If detected early enough, neuroprotective strategies (some already known to researchers) may be able to halt progression before the onset of “overt PD”.
- Early detection will be important for future therapies that stop or slow the progression of Parkinson’s disease; these are the so-called “disease modifying” therapies. The earlier the detection, the more neurons could be saved.
These last two benefits are where we are focusing our research efforts here at Stop Parkinson’s (get our recommendations here).
In order to detect Parkinson’s earlier, prior to obvious movement symptoms, researchers are looking for a combination of early symptoms that accurately predicts Parkinson’s during what is called the “prodromal” phase of PD. The prodromal phase is akin to the incubation period of an infection, and may precede PD diagnosis by up to 20 years.
Nonmotor symptoms include:
- hyposmia (poor sense of smell)
- chronic constipation
- urinary urgency (including frequent nighttime urination)
- rapid eye movement sleep behavior disorder (in which sufferers appear to act out dreams in their sleep)
- daytime sleepiness
These symptoms will continue to worsen and cause an even greater impact on quality of life than the motor symptoms, but they are not specific to Parkinson’s disease and are therefore difficult to use individually for diagnostic purposes.
One of these non-motor symptoms that researchers hoped would be able to predict Parkinson’s was poor sense of smell (hyposmia). Data is conflicting, but some researchers have found hyposmia in more than 96% of Parkinson’s sufferers. The problem is that hyposmia is common to many disorders, and is also a common feature of aging.
The hope was that there would be differences in the ability to detect certain odors between these various disorders, and that Parkinson’s patients would only have a reduced ability to smell a predictable set of odors. If we knew what that set of odors was, we can then predict Parkinson’s far in advance of obvious motor symptoms. Also, once a patient’s doctor finds general hyposmia, that doctor can then run additional tests to determine the source of the hyposmia.
A number of studies were conducted on Parkinson’s patients (and non-Parkinson’s individuals as controls). The above list of scents represents a rough consensus, but also reflects the limited options in the standardized smell tests. Here are a couple of those studies:
Unfortunately, the consensus also appears to be that hyposmia is a general feature of neurodegenerative diseases and that selective scent deficits may not be sufficient to predict or detect Parkinson’s specifically. The unpredictability of these deficits is especially evident across cultures and countries. However, in combination with other nonmotor features of Parkinson’s it may yet have value. Research is ongoing.
The concern about hyposmia is not only about detection and prediction. Reduced sense of smell has a significant impact on quality of life:
- The absence of an olfactory warning function often leads to food poisoning.
- The inability to perceive body odors may lead to insecurity in partnerships or in contact with children, for example.
- The pleasure gained from eating and drinking is greatly reduced.
If you feel that your sense of smell is not what it used to be, see your neurologist.
Researcher at Stop Parkinson's
Dr. Steve is a biochemist, specializing in medical bioinformatics and nutrition. Dr. Steve directs a biomedical consulting laboratory, focusing primarily on biomedical investing and health policy.
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