This ScR included studies on individuals with chronic pain lasting for >3 months. Studies on individuals with malignancy-related or cancer-related pain or acute pain conditions, such as postoperative pain, were excluded. Moreover, studies that included children (≤18 years) and/or participants with other conditions besides chronic pain were excluded. No restrictions were imposed with respect to the sex, location, race, country, or language of the participants. This review evaluated the measurement tools used for sleep assessment in individuals with chronic pain conditions, including polysomnography, wearable devices, and questionnaires. Additionally, we identified various types of pain-related assessments, including pain intensity, severity, disability, catastrophizing, threshold, and tolerance. In other words, we included studies that involved sleep assessments in individuals with chronic pain conditions.

This ScR included randomized controlled trials (RCTs), crossover trials, quasi-RCTs, non-RCTs, cross-sectional studies, and prospective and retrospective cohort studies, encompassing both observational and interventional designs. Protocols and conference abstracts were included in the initial screening, with a secondary screening conducted to verify the existence of published articles. Case reports, case-control studies, systematic reviews, meta-analyses, and narrative reviews were excluded.

The search strategy was designed to identify both published and unpublished studies. A literature search was conducted in MEDLINE, the Cochrane Central Register of Controlled Trials, Embase, PsycINFO, Web of Science, Cumulative Index to Nursing and Allied Health Literature (CINAHL) as well as gray literature sources, Open Grey. In addition, the following trial registries were searched for ongoing or unpublished trials: the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov.

The text words found in the titles and abstracts of relevant articles, along with the index terms used to describe the articles, were used to develop a comprehensive search strategy across nine databases (Table S1). Previous studies were also referenced. ^{17, 21, 22} Studies published in any language were included, with no restrictions on the publication date. The final comprehensive search was conducted on March 29, 2024.

All identified citations were collated and uploaded into Rayyan (Qatar Computing Research Institute, Ar Rayyan, Qatar, https://www.rayyan.ai/), and duplicates were removed. Following a pilot test, two or more independent reviewers (K.T. and Y.I.) screened the study titles and abstracts based on the eligibility criteria. The full text of relevant sources was retrieved, and their citation details were imported into Rayyan. Two or more independent reviewers (K.T., Y.I., K.S., M.H., K.O., and Y.K.) assessed the full text of the selected studies based on the eligibility criteria. The reasons for excluding sources that did not meet the eligibility criteria were documented and reported in this ScR. Any disagreements between reviewers at each stage of selection were resolved through discussion or by consulting additional reviewers.

The results of the search and study inclusion process were comprehensively reported in the final ScR and illustrated in a Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for ScR flow diagram. ²³

Data were extracted from the included studies using Microsoft Excel (Microsoft Corp., Redmond, WA, USA) by the first author (K.T.), with the assistance of ChatGPT-4o (San Francisco, CA, USA) and NotebookLM (Mountain View, CA, USA). ^{24, 25} The extracted data included the first author’s name, country of origin, study design, sample size, participant characteristics (age, sex, and diagnosis), and tools used for assessing sleep disturbance and pain-related outcomes. The draft data extraction tool was modified and refined as necessary throughout the data extraction process. Where necessary, the authors of the included studies were contacted to obtain any missing or additional data.

A total of 3,513 articles were retrieved during the database search. After eliminating 1,296 duplicates, the titles and abstracts of 2,217 articles were screened. Thereafter, the full texts of the remaining 415 articles were assessed for eligibility. Ultimately, only 81 studies that met the eligibility criteria were included in the analysis ( Figure 1).

Of the 81 included studies, 26 (32.1%) were RCTs, ^{26– 51} while the remaining studies were non-RCTs. ^{52– 106} The included studies were published between 1998 and 2024, with nearly half (45.7%, 37 of 81) published within the last 5 years. ^{28– 30, 32– 34, 38, 39, 41, 46, 49– 52, 56, 57, 61, 65, 66, 71, 74, 76– 80, 83– 85, 88– 91, 93, 94, 99, 104} The distribution of participants varied across studies: 31 studies (38.3%) focused on examining patients with chronic pain, irrespective of pain type, accounting for 40.5% of the total participants (7,413 out of 18,316). ^{30, 36, 40, 45, 49, 50, 52, 55, 56, 63, 65, 67– 71, 74, 77, 78, 80, 83, 86, 87, 89, 90, 92, 95, 97, 99, 101, 104} Eleven studies (13.6%) investigated patients with chronic low back pain, accounting for 12.4% of the total participants (2,266 participants). ^{31, 34, 44, 46, 54, 79, 88, 93, 96, 105, 106} Eight studies (9.9%) examined patients with chronic musculoskeletal pain, irrespective of location, accounting for 9.1% of the total participants (1,667 individuals). ^{39, 60– 62, 75, 76, 84, 103} Six studies (7.4%) assessed patients with chronic neck pain, comprising 5.2% of the total participants (950 participants). ^{32, 38, 58, 59, 94, 98}

An overview of the included studies is presented in supplemental materials (Table S2, S3). Various methods have been used to assess sleep problems and pain-related outcomes, with patient-reported outcomes (PROs) being the most frequently utilized.

The Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI) were the most commonly used tools for the assessment of sleep problems. Other self-reported sleep assessment methods used included the Athens Insomnia Scale and sleep diaries. Sleep problems were predominantly assessed based on the participant’s entries in sleep diaries. In terms of study methodology, 73 of 81 studies (90.1%) relied solely on PROs (90.1% [73/81]). ^{28– 51, 58– 106} Only 2 of 81 studies (2.5%) relied solely objective assessments, ^{56, 57} such as actigraphy, whereas 6 of 81 studies (7.4%) used a combination of PROs and objective assessments. ^{26, 27, 52– 55} Other objective sleep assessment methods used included polysomnography and electroencephalography.

For PRO assessments, the outcomes were frequently evaluated using the numeric rating scale (NRS) or visual analog scale (VAS) (58.0% [47/81]). ^{30, 32– 39, 42, 43, 47, 48, 50, 51, 53– 60, 62– 64, 68– 70, 75, 77, 79, 83, 85, 86, 88, 89, 92– 96, 98, 101, 103, 105, 106} The Brief Pain Inventory (BPI) was the second most frequently used pain assessment tool (28.4% [23/81]). ^{26, 28, 29, 31, 40– 42, 44, 45, 49, 55, 61, 65– 67, 71, 74, 76, 78, 80, 84, 87, 97} Additional pain-related outcome measures included the Multidimensional Pain Inventory and Pain Disability Questionnaire. Psychometric factors were evaluated in more than half of the included studies (60.5% [49/81]). ^{28, 30, 33– 36, 39, 40, 42, 45, 47, 48, 50, 52, 53, 56, 58– 61, 67– 77, 81– 83, 85, 88– 93, 95– 97, 100, 101, 103, 104, 106} Objective pain assessment was rarely performed, with only one study utilizing quantitative sensory testing. ⁹⁶

Figure 2 presents the detailed percentages of the combined use of sleep problems and pain-related outcome assessments. The NRS/VAS was frequently used in combination with the PSQI (31.4%), followed by combination of the NRS/VAS with the ISI (15.6%). The simultaneous use of both self-report and objective sleep assessments, along with the NRS or VAS and the BPI, was extremely rare, occurring in only 0.6% of studies ( Figure 2).