Can agitated dreams be an early sign of Parkinson's?

Who has never woken up at night disturbed by a frightening dream? Bad dreams are very common and usually have no clinical significance. However, scientific research in recent decades has identified a particular type of sleep disorder - one in which one acts physically while dreaming, moving, screaming or falling out of bed - that may be an early sign of certain neurological diseases, such as Parkinson's disease. This is a rapidly evolving area of research that is changing the way doctors look at sleep disorders as possible alarm bells of more serious diseases. On the occasion of World Parkinson's Day on 11 April, we shed some light together.

Sleep consists of several phases that alternate during the night. One of these, called the REM phase (from Rapid Eye Movement), is the one in which one dreams the most. Under normal conditions, during the REM phase the muscles of the body are temporarily 'blocked': the brain dreams, but the body does not move. In REM sleep behaviour disorder - referred to as RBD (Rapid eye Movement sleep Behaviour Disorder) - this blocking mechanism does not work properly. The sufferer actually moves while dreaming: he or she may scream, kick, gesticulate forcefully, or even fall out of bed, often in response to vivid dreams in which one is fighting or running away from something. It is often the bed partner who first notices.

This disorder was first described in 1986 by the American neurologist Carlos Schenck, who had observed a group of elderly patients with these nocturnal behaviours. Today we know that RBD, especially when it has no apparent cause such as a side effect of a drug, can be a very early sign of neurodegenerative diseases, i.e. diseases that progressively damage the nervous system.

Yes, today this link is well documented in the scientific literature. In one of the first long-term studies on the subject, a group of researchers from the University of Barcelona followed patients with RBD over time, observing that many of them developed Parkinson's disease or dementia with Lewy bodies, a neurological disease that affects both movement and memory. This finding was later confirmed by an international multicentre study that collected data from 24 specialised centres around the world: on a very large case series, the researchers confirmed the high risk of conversion to neurodegenerative disease and identified certain signs that, if present along with RBD, further increase this risk. These include loss of sense of smell, mild memory difficulties and some still subclinical motor signs. A systematic review with meta-analysis then estimated that about one third of sufferers develop synucleinopathy - a term doctors use to refer to a group of diseases that includes Parkinson's, Lewy body dementia and other similar conditions - within five years of diagnosis, and that this percentage could exceed 90 per cent over the course of 14 years.

Research on this point is still in its early stages and the available evidence is less robust than that on RBD. A study published in 2022 analysed data from three large British population cohorts. The results showed a statistically significant association between the presence of frequent nightmares and an increased risk of developing Parkinson's disease over the next five years.