medwireNews: Predictive markers can identify patients with REM sleep behaviour disorder (RBD) who have a very high short-term risk of developing parkinsonism or dementia, research suggests.
Stratification of RBD patients using markers such as age, olfactory function and motor function allowed Jacques Montplaisir (Université de Montréal, Québec, Canada) and team to identify patients with a more than 60% rate of conversion to parkinsonism or dementia over a 3-year period.
“[O]ur findings suggest that it is now not only possible, but also practical to include patients with RBD in neuroprotective trials”, they write in Neurology.
Of the 89 patients studied, 41 developed disease during follow-up lasting an average of 5.4 years. Twenty patients were diagnosed with primary parkinsonism, according to the UK Brain Bank criteria, and 21 with dementia, according to the Movement Disorder Society criteria. In the latter group, 18 patients had at least one cardinal parkinsonism sign, and 11 met the full criteria for parkinsonism.
The researchers calculated that RBD patients have a neurodegenerative disease risk of 30% at 3 years, 47% at 5 years and 66% at 7.5 years. “[I]n fact, it appears that only a small minority of patients do not have an underlying neurodegenerative process”, they observe.
And this risk could be further defined using markers that significantly increased the likelihood of conversion: older age, impaired olfactory function, abnormal colour vision and evidence of motor dysfunction on at least two of four measures.
Conversely, patients who were taking antidepressants had a significantly reduced likelihood of conversion to a neurodegenerative disease.
The calculated 3-year conversion rate rose from 30% for all RBD patients, to 35% if they were older than 55 years and did not use antidepressants, and to 44%, 49% and 65% if they additionally had impaired olfaction, abnormal colour vision or motor dysfunction, respectively.
This would reduce the number of patients required per group in a trial of a moderately effective agent from 134 to 72, say Montplaisir et al.
They say: “A major reason for the failure to develop neuroprotective synucleinopathy therapy may be that the disease has been present many years before clinical parkinsonism or dementia; it is simply too late to intervene.”
By selecting patients with RBD, researchers can potentially treat them before neurodegeneration becomes too advanced, they explain, while stratifying patients according to the identified risk markers reduces the number required to demonstrate efficacy.
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