Until 2002, there were no specific instruments to clinically assess sleep problems of PD in a comprehensive and holistic fashion. Existing sleep scales for other disorders, such as the Pittsburgh Sleep Quality Index (PSQI), Stanford Sleepiness Scale, or the Karolinska Sleepiness Scale, are not specific for PD and have problems related to scale clinimetrics in relation to complexity and face validity when these are used in PD (66, 71-73). For instance, the PSQI, although quantifiable, does not specifically address sleep disturbances of PD, such as restlessness of legs, painful posturing of arms or legs, tremors, or fidgeting. The Stanford Sleepiness Scale and the Karolinska Sleepiness Scale appear too short for a comprehensive assessment of sleep problems. The gold standards for measurement of physiological aspects of sleep architecture are PSG and MSLT. However, these are tests of sleep structure, need specialized sleep laboratories, and can be expensive. In the United Kingdom, for instance, facilities for sleep studies are scarce and not readily available. Furthermore, these studies do not provide any information on aspects of sleep dysfunction in PD, such as nocturnal tremor, akinesia, nocturia, or hallucinations.
The Unified Parkinson's Disease Rating Scale is widely used for motor assessments in PD and contains only one sleep-related inquiry: "Does the patient have any sleep disturbances, for example, insomnia or hypersomnolence?" (74). As such, this is inadequate for sleep assessment of PD and a proposed revision of the scale may have more sleep related items incorporated (74,75).
The ESS is a self-administered questionnaire, aimed toward assessment of EDS in eight situations of daily life (76). The ESS is widely used in PD and correlates well with the relevant question (question 15) on the PDSS. The study by Meindorfner et al. (57) suggested that a high ESS score in a patient with moderately advanced PD may predict a risk for sudden onset of sleep and road traffic accidents. However, the ESS does not quantify the types of sleep disturbances that occur in PD. Furthermore, the interpretation of the ESS suffers from cross-cultural differences and uncertain test-retest reliability.
The first bedside scale for a comprehensive assessment of sleep problems was validated and published in 2002 and is the PDSS, which has now been translated globally and used across the world for a bedside assessment of clinical aspects of sleep disabilities of PD (65,66). The PDSS is a 15-question visual analog scale, which can be easily administered at the bedside and has also undergone formal linguistic validation in Italy, Spain, and Japan (66,77). The PDSS has robust test-retest reliability and good discriminatory power between patients with PD and healthy controls. Patients and caregivers respond to individual questions on the basis of their experiences in the past week, and scores for each item range from 0 (symptom severe and always experienced) to 10 (symptom free). The maximum cumulative score for the PDSS is 150 (patient is free of all symptoms). The PDSS aims to distinguish between sleep onset and sleep maintenance insomnia (questions 2 and 3); nocturnal motor symptoms (questions 10 to 13); nocturnal restlessness, dystonia, and pain (questions 4, 5, 10, 11); neuropsychiatry symptoms (questions 6 and 7); and nocturia (questions 8 and 9). EDS is addressed by question 15, whereas question 14 addresses sleep refreshment. A total score below 90 or an individual item score below 6 is likely to indicate significant sleep disturbance. One criticism is that PDSS does not specifically address the issue of sleep-disordered breathing and RBD, and a modification has been suggested (78).
As part of a program for development of scales to address various aspects of PD (SCOPA), Marinus et al. (79) have also developed and validated the SCOPA-Sleep Scale. This is a short, two-part scale that assesses nocturnal sleep and daytime sleepiness, and contains nondisease-specific items. The SCOPA-Sleep Scale has been validated in PD and is reliable, but unlike the PDSS, it is not a visual analog scale and does not address some problems specific to PD, such as nocturnal hallucinations, pain, dystonia, tremor, and nocturia, which can be quantified in the PDSS.
Sleep architecture can be studied using PSG, and MSLT provides measures of alertness. These studies are not routinely required for the assessment of sleep in PD. However, in cases where obstructive sleep apnea or severe PLM is suspected, PSG is essential. In cases of severe RBD or other parasomnias, PSG is useful for confirmation of diagnosis. A pathological MSLT result (sleep latency <10 minutes) in a PD patient may also suggest a propensity to sudden onset of sleep.
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