Insomnia is a common complaint in Parkinson's disease (PD) affecting more than three-quarters of patients. Longitudinal studies show that insomnia complaint is a persistent condition in PD, especially in patients with more severe insomnia at baseline. When international and standardized criteria are used, it is estimated that more than half of the patients meet the criteria for insomnia disorder. These data define insomnia as the most prevalent sleep disorder in PD. Given that background, it is surprising that none of the scales recommended by the International Parkinson and movement disorder society to assess sleep disturbances in PD is specifically dedicated to the assessment of insomnia disorder. In this insufficient methodological context, we have recently established the discriminant validity of the Sleep condition indicator for insomnia disorder in PD, as diagnosed with a clinical interview according to the DSM-5 criteria. As in the general population, female sex, symptoms of depression, anxiety, fatigue and daytime sleepiness have been associated with insomnia complaint severity in PD. Insomnia also reduces the quality of life of patients affected by PD and that of their caregivers. In contrast, clinical features of the disease were very slightly related to insomnia with small effect sizes. These features include motor fluctuations, autonomic problems, cardiovascular and thermoregulatory dysfunctions and doses of dopaminergic medications. This observation implies not systematically considering insomnia as a symptomatic manifestation secondary to PD but as a clinical entity requiring specific treatment. The objective of this synthesis is to raise awareness among health professionals of the importance of early detection of insomnia in PD in order to limit the consequences associated with its chronicity. Identifying and assessing insomnia in PD is therefore a major health issue.
Keywords: Parkinson's disease; Sleep condition indicator; insomnia; risk factors; sleep.