WASHINGTON – Researchers in Japan have used functional magnetic resonance imaging to identify brain activation deficits associated with olfactory dysfunction in patients with Parkinson's disease, according to data presented at the World Parkinson Congress.
In a study of 10 patients with Parkinson's disease (PD) compared with 10 healthy controls, the researchers found significant brain activation in the cerebral cortex in control patients exposed to strong odorants, while PD patients showed little brain activation. Olfactory dysfunction appears to be one of the earliest symptoms of the disease.
“In PD, brain activation by odorant stimulation was significantly decreased. Hyposmia in PD is not a simple reflection of impairment in sniffing,” said Atsushi Takeda, Ph.D., of Tohoku University in Sendai, Japan.
The PD study participants had an average Hoehn and Yahr stage score of 2.2 and their mean L-dopa dosage was 243 mg. “So they were in the early stage of Parkinson's disease,” Dr. Takeda noted.
However, current olfactory tests for early PD detection rely on subjective responses by the patient and can potentially be influenced by environmental factors, such as temperature and humidity. “Most importantly, possible impairment in sniffing, as one of the motor symptoms of Parkinson's disease, may influence olfactory perception,” said Dr. Takeda.
The researchers used vanillin and toluene as olfactory stimulants. Patients were exposed to no odorants for 30 seconds, followed by odorant exposure for 30 seconds. This cycle was repeated six times.
To maintain constant odorant stimulation during the “on” periods, the researchers designed a special system with an evaporator and computer-controlled valves to allow exposure to the odorant and a high-pressure compressor to move the odorant to the subject wearing a face mask in the MRI tube. The researchers used a 1.5-T machine to obtain T2* images that were analyzed using statistical parametric mapping.