What is REM-sleep Behavior Disorder?
REM-sleep Behavior Disorder (RBD) is a parasomnia characterized by abnormal behaviors that emerge during REM sleep, potentially leading to injury. Prevalence of RBD has been estimated at 0.5%, being more common in males, with onset typically occurring in those aged 50 years and over.
Symptoms of RBD
Rapid eye movement (REM) sleep is the phase of sleep where we are most likely to experience intense and vivid dreaming. It is normally characterized by muscle atonia (a loss of muscle tone), meaning that we are essentially paralyzed during this phase of sleep and should therefore, be unable to initiate any motor movements. This loss of muscle tone can be measured through a technique called electromyography (EMG), as part of overnight sleep study or 'polysomnography' (PSG), which determines electrical activity in skeletal muscles. In those with RBD however, there is no loss of muscle tone during periods of REM sleep, leaving these patients able to act out their dreams.
In contrast to those with NREM (non-rapid eye movement) parasomnias, such as sleep-walking, patients with RBD often have good recall of the dream and are able to orient themselves to their surroundings relatively quickly after arousal. Dreams are often described by RBD patients as being vivid, intense and action-packed. In terms of behavior, dream-enacting episodes can typically feature confrontation and aggression, which can result in injury to the patient (e.g. diving from bed) and bed partner (e.g. choking/headlock). It is often the case therefore that RBD patients will first present to a sleep medicine specialist due to a history of sleep-related injury. Typically, these injuries will range from bruises and tooth chipping through to lacerations, fractures and subdural hematomas (Schenck & Mahowald, 2011).
What causes RBD?
There is evidence that brainstem areas of the brain are involved in regulating REM sleep and that damage to these areas may result in RBD-like symptoms. This is supported by research into lesions in certain brainstem areas (in particular the pontine tegmentum), which induced human-like RBD symptoms in cats.
Recent follow-up studies of patients diagnosed with RBD have also shown that more than half of all patients subsequently develop neurodegenerative disorders, particularly Parkinson's Disease and Dementia with Lewy Bodies. Effective pharmacological treatment usually involves Clonazepam, which appears to suppress excessive motor-behavioral activity during REM sleep. Melatonin is also used as a second-line therapy in RBD patients, which has been shown to restore normal REM muscle atonia in some patients. In conjunction with pharmacotherapy, maximizing the safety of the sleeping environment is also important e.g. move bed away from window, bed partner sleep in a different room, move hard objects away from bed area (Schenck & Mahowald, 2011).