Clinically relevant cut-off values for the Parkinson's Disease Sleep Scale-2 (PDSS-2): a validation study

Background: Sleep disturbances are a major problem encountered by neurologists attending Parkinson's disease (PD) patients. The Parkinson's Disease Sleep Scale-2 (PDSS-2) assesses a wide spectrum of disease-specific sleep problems and is easy to administer as a patient self-rating scale. The validation study showed that the scale is reliable, valid, and precise. Until now, however, only one Japanese study has assessed cut-off scores to define poor sleepers.

Objectives: In this context we aimed to determine the PDSS-2 cut-off values that define a sleep disturbance severe enough to require referral of the patient to a sleep center or the need for specific treatment.

Methods: Inpatients with idiopathic PD consecutively admitted to our hospital were enrolled. Patients completed the PDSS-2. The attending physician, who was blinded to the PDSS-2 results, but familiar with the patients' history and current disease status, completed a questionnaire consisting of two general questions on the presence of PD-specific and non-PD related sleep problems. Statistical analysis was performed to determine cut-off values for the PDSS-2 and correlation with the physician's evaluation of sleep disturbance severity. A natural cohort of non-PD patients with sleep disorders represented the control group.

Results: The sample consisted of 52 (56%) men and 41 (44%) women with an average age of 69.22 ± 8.74 years. PDSS-2 showed a sensitivity of 77.6% and a specificity of 74.3% in relation to physician's evaluation of PD-specific sleep problems. According to the physician's evaluation, PD-specific sleep disturbances occurred in 62% of the patients. 83% of patients with PDSS-2 scores ≥18 had clinically relevant sleep disturbances compared to only 33% of PD patients with scores <18. The severity of PD-specific sleep problems was well correlated with the PDSS-2 total score (r = 0.49).

Conclusions: To our knowledge, this is the first study to define PDSS-2 cut-off values for the severity of sleep disturbances in a European PD sample. Our study shows that scores ≥18 define clinically relevant PD-specific sleep disturbances.