In both retrospective (Iranzo et al., 2006) and prospective (Postuma et al., 2009) analyses, researchers have found that about half of RBD patients develop PD or another synucleinopathy within a decade or so. However, not nearly everyone with RBD has an evolving neurodegenerative disorder, said Bradley Boeve of Mayo Clinic, Rochester, Minnesota, in an interview with ARF. Furthermore, the interval between an initial report of sleep problems and first signs of cognitive decline can vary considerably—from 15 to 50 years in Boeve’s recent retrospective of long-duration RBD (Claassen et al., 2010 and ARF related news story). So what is a clinician to tell someone with RBD?

Aiming to narrow down who may truly be on the verge of developing PD or other synucleinopathies, Iranzo and colleagues put two brain imaging tools to the test in a longitudinal study of 43 people with diagnosed RBD. In one method, single photon emission computed tomography (SPECT) imaging uses a 123I-radiolabeled ligand to measure levels of dopamine transporter (DAT), which are typically reduced in the substantia nigra of PD patients due to steep cell loss in this brain area. In addition, the researchers looked for brain abnormalities in the RBD patients using an ultrasound method that detects regions with increased iron deposition, which has been suggested to be involved in PD (Walter et al., 2010). The trouble spots in the substantia nigra bounce echo unusually well and show up on the sonogram as “hyperechogenicities.”

Iranzo and colleagues found that they were correct to suspect that these neuroimaging changes typical of early PD would also show up in people with the sleep disorder. When assessed 2.5 years after brain imaging, 27 of the 43 RBD patients had either reduced striatal dopamine activity, midbrain hyperechogenicity, or both. Among these 27 with PD-like brain changes, eight developed a synucleinopathy after 2.5 years follow-up. Five had PD, two had dementia with Lewy bodies, and one had multiple system atrophy. Of the 15 participants who looked normal by both brain imaging tools, none developed a neurological syndrome during follow-up.

An obvious question is whether those who had something amiss in their neuroimaging, but remained neurologically sound during this study, will eventually show signs of PD or the other disorders. Continued clinical follow-up of these patients should help address this issue, Iranzo said.

The current work adds to a growing body of literature supporting the use of DAT imaging for clinical as well as research purposes, Boeve told ARF. The technique is approved in Europe, and used mainly on patients who have atypical PD symptoms and/or lack cardinal clinical features, though also sometimes for routine diagnosis. In the U.S., though, DAT imaging has not even entered the research arena. The Peripheral and Central Nervous System Drugs advisory committee of the U.S. Food and Drug Administration (FDA) has voted to recommend DAT imaging to the FDA, and the FDA decision is pending. Many clinicians and researchers in the U.S. are planning to use DAT imaging once approved.”

To date, the ultrasound method has been used in Europe as well, Boeve noted, with comparatively few U.S. studies featuring the technique.

The current work “underscores the usefulness of studying adequate numbers of patients longitudinally with a spectrum of clinical tests and potential biomarkers to assess the natural history of RBD and prepare for future clinical trials,” Boeve wrote in an accompanying editorial.—Esther Landhuis.

Reference:
Iranzo A, Lomeña F, Stockner H, Valldeoriola F, Vilaseca I, Salamero M, Molinuevo JL, Serradell M, Duch J, Pavia J, Gallego J, Seppi K, Högl B, Tolosa E, Poewe W, Santamaria J, for the Sleep Innsbruck Barcelona (SINBAR) group. Decreased striatal dopamine transporters uptake and substantia nigra hyperechogenicity as risk markers of synucleinopathy in patients with idiopathic rapid-eye-movement sleep behaviour disorder: a prospective study. Lancet Neurol. 2010 Sep 15. Abstract