Optimal Screen for Early Parkinson's Still Elusive

MIAMI BEACH – Widespread screening for early Parkinson's disease with olfactory testing followed by neurologic imaging holds promise but is not yet practical, based on studies that have revealed the limitations of each method.

Olfactory impairment is common enough in premotor Parkinson's that some researchers propose using it as an early predictor of risk (Ann. Neurol. 2008;63:167-73).

However, olfactory testing has not garnered widespread adoption because it lacks sufficient specificity for population-based screening, Dr. Henk W. Berendse said at the congress. He and others have proposed coupling olfactory testing with highly specific brain imaging, such as dopamine transporter single-photon emission computed tomography (DAT SPECT).

There is a catch, though. The imaging would have to be done in a large number of individuals, many of whom would not develop Parkinson's disease, said Dr. Berendse, head of the movement disorders service at the VU University Medical Centre in Amsterdam.

In a subsequent presentation at the meeting, Dr. Andrew D. Siderowf of the neurology department at Pennsylvania Hospital in Philadelphia called population screening for Parkinson's disease a “numbers game.”

The incidence of Parkinson's disease is low, so the number of potentially identifiable cases in a population at any given time also is low, he said.

In 2005, the worldwide prevalence of the disease was estimated to be between 4.1 million and 4.6 million (Neurology 2007;68:384-6).

Dr. Berendse calculated that “if you expect to detect 125 patients in the premotor phase [of Parkinson's disease], somewhere between 1,000 and 7,000 individuals would have to undergo SPECT scans. Assuming a 10% prevalence of hyposmia, we would need to screen 70,000 individuals.”

The 10% prevalence of hyposmia is based on a study that screened 361 asymptomatic, 50- to 75-year-old relatives of patients with idiopathic Parkinson's. All of the relatives had olfactory testing, and the 40 who tested positive also had serial

Dr. Berendse and Dr. Siderowf had no relevant financial disclosures.