Patients with REM sleep behaviour disorder, a condition in which people violently act out their dreams during the rapid eye movement cycle of sleep, have been found to develop Parkinson’s and related neurological disorders as much as a half century later.
The study used the Mayo medical records linkage system to identify cases presenting from 2002 to 2006 meeting the criteria of idiopathic REM sleep behaviour disorder at onset, plus at least 15 years between REM sleep behaviour disorder and development of other neurodegenerative symptoms.
“Our findings suggest that in some patients, these conditions have a very long span of activity within the brain and they may also have a long period of time where other symptoms are not apparent,” said study author Bradley Boeve, from the Mayo Clinic in Rochester, USA.
“If you can intervene when the disease is still at the brain stem and not affecting some other critical structure in the brain, hopefully at the very least we can slow it down,” he added.
All patients underwent evaluations by specialists in sleep medicine to confirm REM sleep behaviour disorder, and behavioural neurology or movement disorders to confirm subsequent neurodegenerative syndrome. Criteria were met by 27 patients who experienced isolated REM sleep behaviour disorder for at least 15 years before evolving into neurological disease. The interval between REM sleep behavior disorder and subsequent neurologic syndrome ranged up to 50 years, with the median interval 25 years. At initial presentation, primary motor symptoms occurred in 13 patients. Primary cognitive symptoms also occurred in 13 patients. At most recent follow-up, 63% of patients progressed to develop dementia. Concomitant autonomic dysfunction was confirmed in 74% of all patients.
These cases illustrate that the synuclein pathogenic process may start decades before the first symptoms of PD, DLB, or MSA. A long-duration preclinical phase has important implications for epidemiologic studies and future interventions designed to slow or halt the neurodegenerative process.
“This is important for us understanding the progression of the disease because this RBD obviously precedes other clinical manifestations of Parkinson’s by many years,” said Michael Thorpy, Montefiore Medical Center, New York, USA.