Early Parkinson’s and REM disorder: a study of 413 people

A study of the PPMI cohort (Parkinson's Progression Markers Initiative), published in 2024 in Annals of Clinical and Translational Neurology, followed 413 people with de novo Parkinson's, early in the disease and not yet on treatment, for five years. At the start, 105 had probable REM sleep behaviour disorder (pRBD), assessed with a questionnaire.

What REM sleep behaviour disorder is

In normal conditions, muscles are paralysed during REM sleep. In REM sleep behaviour disorder this paralysis is absent, and the sleeper physically acts out the content of dreams.

It is considered a possible early sign of neurodegeneration and is often present years before a diagnosis of Parkinson's or Lewy body dementia.

People with pRBD at the start showed faster decline in global cognition and in every cognitive domain tested: verbal episodic memory, visuospatial ability, executive function, language and processing speed. pRBD was also associated with a decrease over time of beta-amyloid (Aβ42) in the cerebrospinal fluid, one of the Alzheimer's biomarkers, and with a higher risk of developing dementia. The authors note one limit: the disorder was assessed with a questionnaire, not an instrumental test.

Implications for early diagnosis

For someone with Parkinson's, knowing that REM sleep behaviour disorder is present can help the neurologist follow memory and other cognitive functions more closely. The study describes an association in a group of people. It does not say what will happen to any one person, and decisions about care are for the treating doctor.

A ring or a watch records movement at night, but this disorder is diagnosed with a clinical test, polysomnography. The Digital Twin lines up the data your devices write to your phone, such as steps, heart rate and sleep, and shows you how they change over time. It does not recognise this disorder and it does not diagnose: this research describes groups of people, not you. If the person who sleeps next to you notices that you thrash, talk or lash out in your sleep, talk to your doctor.