Olfactory Impairment Can Precede Development of Parkinson's Disease

A study has shown that an odor identification deficit can predate the development of Parkinson's disease (PD) by at least four years, although it is not a strong predictor beyond this period.

More than 2,000 men from the Honolulu-Asia Aging Study who received olfactory testing at least once, either between 1991 and 1993 or between 1994 and 1996, were followed for up to eight years to find out if they developed PD. During the course of follow-up, 35 men developed the disease. The study was performed at Kuakini Medical Center (Honolulu, Hawaii, USA).

Decreased odor identification was associated with older age, smoking, more coffee consumption, less frequent bowel movements, lower cognitive function, and excessive daytime sleepiness, but even after adjusting for these factors, those with the lowest olfactory scores, meaning they had the poorest odor identification, had a five times greater risk of developing PD than those with the highest scores.

The pathology of smell impairment in PD is not completely understood, but nerve loss and the formation of Lewy bodies, abnormal clumps of proteins inside nerves cells that are thought to be a marker of PD, are known to take place in the olfactory structures of patients with the disease. A study involving brain dissection of deceased patients with neurologic disease found that olfactory structures are the earliest brain regions affected by Lewy degeneration, which supports the idea that an impaired sense of smell could be one of the earliest signs of the disease.

The study was published in the March 21, 2008, Annals of Neurology, the official journal of the American Neurological Association.


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Kuakini Medical Center