Loss of smell may precede Parkinson's disease

By David Douglas

NEW YORK (Reuters Health) - An impaired sense of smell is known to be associated with Parkinson's disease -- and now a study in the Annals of Neurology shows that the loss of smell may predate the onset of clinical symptoms by several years.

"Olfactory screening could help in the early detection of Parkinson's disease before the typical motor signs are evident," lead investigator Dr. G. Webster Ross told Reuters Health.

Ross of the VA Pacific Islands Health Care System, Honolulu, and colleagues evaluated data from a standardized test of odor identification from 2,267 men of Japanese ancestry participating in an aging study. All were free of clinical Parkinson's disease and dementia at the time of testing. The average age at study entry was 80 years old and the men were followed for up to 8 years.

During follow-up, 35 men were diagnosed with Parkinson's disease, giving an overall incidence of 24.6 cases per 10,000 persons per year. The average time to diagnosis was 4 years and the average age was 83 years.

After taking into consideration the potential influence of age, the incidence of Parkinson's disease was 8.4 per 10,000 persons per year for those with the highest smell identification scores and 54.5 per 10,000 persons per year in those with the lowest scores.

After adjustment for age plus other potential confounders, the men with the lowest odor recognition scores had 5.2-times the odds of developing Parkinson's disease compared with those with the highest scores.

The researchers conclude that an impaired sense of smell "may be a useful screening tool to detect those at high risk for development of Parkinson's disease in later life." This, added Ross, "will become very important when there are interventions available to halt or slow progression" of Parkinson's disease.

SOURCE: Annals of Neurology, February 2008.