Test to Detect Loss of Sense of Smell in Parkinson’s Disease

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Can  a simple test to detect the loss of the sense of smell be useful in making earlier and more accurate diagnoses of Parkinson’s?  A team of Dutch researchers  think so.   At least 90% of all Parkinson’s patients experience loss of their sense of smell, and many studies have verified this.  This study found an easy and inexpensive test  that can be used in a clinical setting to help diagnose PD accurately .

This clinical trial recruited  much larger numbers of participants than many trials which are sometimes limited by having fewer Parkinson’s patients.  This gives this trial’s accuracy a stronger and more favorable outcome.  296 people were enrolled, 148 as age matched healthy controls and 148 Parkinson’s patients.  The PD patients were divided into three groups by symptoms: rigidity as dominant symptom, . tremor as dominant  or other symptoms.

All participants were asked to identify 16 different odors to identify which odors would be appropriate for a more sensitive test.  “Sniffin’ Sticks”, a product specific for olfactory testing, were used enclosed in felt tip pen cases to conceal their identities.   Odors included food odors such as fish, peppermint, coffee, cloves, cinnamon, etc and non food odors such as rose, gardenia, leather, etc.   Food odors had the best sensitivity ratings and were then narrowed down to eight and then again down to three.  Ultimately, the three odors that demonstrated the best sensitivity contrast between healthy controls and Parkinson’s were coffee, peppermint and anise.

All the healthy controls were able to identify these odors and only 10 of 148 in the Parkinson’s group. This appeared to be age related responses from younger members of the Parkinson’s group; however younger members (ages 45 – 65) of the PD  group already showed significant olfactory impairment compared to the age matched controls.  Severity of the disease also was important.  The group that was rigidity-dominant had slightly more olfactory impairment than the tremor group.  Cognition was another  indicator of odor impairment, but the results were sensitive to the type of  cognitive testing used.   Women and smokers showed a somewhat lower risk for impairment.

Results of this trial show a strong correlation between sense of smell and Parkinson’s.    Testing odor identification  can be a useful supportive diagnostic tool for Parkinson’s.   A brief three odor smell test in a clinical setting  is a non-invasive, cost effective tool  that could help both patients and neurologists.

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