Idiopathic REM sleep behaviour disorder in the development of Parkinson's disease.

Parkinson's disease is a progressive neurodegenerative disorder associated with Lewy body disease pathology in central and peripheral nervous system structures. Although the cause of Parkinson's disease is not fully understood, clinicopathological analyses have led to the development of a staging system for Lewy body disease-associated pathological changes. This system posits a predictable topography of progression of Lewy body disease in the CNS, beginning in olfactory structures and the medulla, then progressing rostrally from the medulla to the pons, then to midbrain and substantia nigra, limbic structures, and neocortical structures. If this topography and temporal evolution of Lewy body disease does occur, other manifestations of the disease as a result of degeneration of olfactory and pontomedullary structures could theoretically begin many years before the development of prominent nigral degeneration and the associated parkinsonian features of Parkinson's disease. One such manifestation of prodromal Parkinson's disease is rapid eye movement (REM) sleep behaviour disorder, which is a parasomnia manifested by vivid dreams associated with dream enactment behaviour during REM sleep. Findings from animal and human studies have suggested that lesions or dysfunction in REM sleep and motor control circuitry in the pontomedullary structures cause REM sleep behaviour disorder phenomenology, and degeneration of these structures might explain the presence of REM sleep behaviour disorder years or decades before the onset of parkinsonism in people who develop Parkinson's disease.