Diagnostic Validity of the Sleep Condition Indicator to Screen for Diagnostic and Statistical Manual-5 Insomnia Disorder in Patients with Parkinson's Disease

Background: Insomnia is a highly common sleep disorder in patients with Parkinson's disease (PD). Yet, no screening questionnaires following the Diagnostic and Statistical Manual-5 (DSM-5) criteria have been validated in PD patients. Objectives: We assessed the validity and reliability of the French version of the sleep condition indicator (SCI), in patients with PD. Methods: In a sample of 65 patients (46% women, mean age 63.8 ± 7.9 years) with PD, but without dementia, insomnia was assessed with a clinical interview and the SCI. Statistical analyses were performed to determine the reliability, construct validity, and divergent validity of the SCI. In addition, an explanatory factor analysis was performed to assess the underlying structure of the SCI. Results: Of the 65 patients (mean duration PD 9.7 ± 6.9 years), 51% met the criteria for insomnia disorder when measured with a clinical interview. The mean SCI score was 18.05 ± 8.3. The internal consistency (α = 0.89) of the SCI was high. Using the previously defined cutoff value of ≤16, the area under the receiver operating characteristic curve was 0.86 with a sensitivity of 86% and a specificity of 87%. Exploratory factor analysis showed a 2-factor structure with a focus on sleep and daytime effects. Additionally, good construct and divergent validity were demonstrated. Conclusion: The SCI can be used as a valid and reliable screener for DSM-5 insomnia disorder in PD patients. Due to its short length, it is useful in both clinical practice and scientific research.