Chronic pain can be a symptom of a primary pain syndrome, in which pain cannot be accounted for by another pain condition or underlying disease, or a secondary pain syndrome, in which pain is linked to other diseases as the underlying cause (1). Almost 18%–34% of adults in the United States and Europe are affected by chronic pain (2, 3). Physical functioning and quality of life (QOL) are often negatively affected in chronic pain syndromes (4, 5). As became clear in the last decades, pain-related disability has a biopsychosocial character. As we know from research in primary pain syndromes, (dynamic) psychosocial factors interact and interfere with daily functioning in chronic pain (6–8). Their joint impact potentially accounts for changes in pain intensity and pain-related disability (9). In secondary chronic pain syndromes, biomedical factors can even lead to an additional disabling impact. Fluctuations in somatic symptoms related to the underlying medical disorder also may negatively interact with psychosocial factors leading to a pain as well as daily functioning with a joined impact on pain intensity and disability (9–11). The treatment of the underlying disease in a secondary chronic pain syndrome will not automatically result in the improvement of pain intensity or QOL with disease management. However, the impact of pain is not always investigated with a biopsychosocial approach (12, 13). It is necessary to be aware of the pain management and the underlying biopsychosocial factors in order to unravel and understand fluctuations of all biopsychosocial factors over time and their impact on QOL, pain and pain-related disability to develop a personalized treatment approach (9, 11, 14–19).

Pain intensity, psychosocial factors (including catastrophizing, fear, anxiety, and depression) and biomedical factors (such as f.e., spasticity in spinal cord injury related pain or disease activity in rheumatoid arthritis) as well as daily activities are not stable but may fluctuate and change throughout the day (11, 20). Measuring changes in these factors within a day, (probably) influencing pain intensity and pain-related disability, is possible with a diary. This contrasts standard questionnaires, which cannot be used for the momentary assessment of biopsychosocial factors (21). Moreover, these questionnaires are not able to capture daily changes as they need the support of the memory to recall symptoms and pain over a certain period (22). As a result, retrospective assessments are prone to result in an over- or underestimation of complaints (15, 17, 23–27). In contrast, real-time changes can be assessed with a daily diary, which avoids recall and memory bias (27).

The experienced sampling method (ESM) is a smartphone-based diary (application), that gathers real-time repeated measurements at randomly determined moments in the natural environment of everyday complaints (9, 16, 22, 28–31). A more profound understanding of disease-related fluctuations, including mood, somatic symptoms, thoughts, and physical activity, can be monitored (11, 15–17). Several beep signals per day are sent as a reminder to fill in a set of questions and statements for a consecutive period, which could result in a burden. In order to measure the fluctuations of the biopsychosocial factors with ESM, a feasibility study has to confirm the acceptability, usability and feasibility of ESM. Various feasibility studies have proven ESM to be valid and reliable in the daily-life assessment of primary chronic pain (9, 15, 17, 32). However, several predictors have been clarified, negatively influencing the response rate, including male gender, younger age, substance abuse, and negative affect (22, 33–36). There are also a couple of requirements for the successful use of ESM to prevent missing data, e.g., being able to use a smartphone and thinking of a low battery to charge in time (37). However, the exact addition of ESM data to the clinical practice remains unclear.

The aim of this study is to analyze the acceptability, usability, and feasibility of ESM in chronic secondary neuropathic pain syndromes and chronic secondary musculoskeletal pain syndromes, in a single-center study in the Netherlands.

In this study, we investigated the acceptability, usability, and feasibility, of ESM in 34 participants with chronic secondary neuropathic musculoskeletal pain syndromes. The overall response rate was 44.5%, with a range between 13% to 97%. Measuring acceptability and usability of revealed favorable outcomes for ESM.

In earlier ESM studies in participants with a psychiatric diagnosis or a primary chronic pain syndrome, the response rate (compliance) was reported to be between 71.1% and 86% (22, 32, 35). We found a response rate of 44.5%, which is above our pre-set minimum of 33% (39), but remarkably lower than the abovementioned samples. Several factors can be related to this difference: We will divide this into participant- or application-related issues. Participant-related issues will first be discussed. Both, a younger or older age, could result in (more) missing values. Younger participants are mostly carefree with less responsibility, and an increasing missing data over participation time (33–35). On the contrary, an older age could be accompanied by (more) technological difficulties, when compared with a younger age (42). In our data, the age range was 23–77 (mean 54.7 ± 13.9 years). Nonetheless, within our group of participants, we did not find any age-related association. Another explanation could be gender. It has been reported that missing rates are much higher in male participants (34). Forty-seven percent of our participants are males, but no association between the number of missing rates and male gender could be identified. Neither for the association between the missing rate and substance abuse (tobacco, alcohol, and drugs), negative affect, and educational level [p-value >0.998, 95% CI (0.00–0.00)] (22, 35, 43–45). Moreover, no differences were found between the three different secondary chronic pain disorders. We can cautiously indicate that participant-related factors probably did not influence the amount of missing data and completion rates.

As previously mentioned, application-related factors could also have contributed to missing data. Although, the number of 10 beep signals per day was reported to be feasible enough (29), however, why do we observe a low completion rate when compared to earlier ESM research? Only 44.5% of all questions and statements were filled in (1058/2520). This means that per participant, an average of 31 of the totals of 70 beep signals (10 beep signals per day for 7 days) were completed. Could ESM create an intrusive threshold? A high number of beep signals could create an intrusive threshold, resulting in a burden. The results of the general and user-friendliness evaluation reported however less interference when compared to scores when compared to other literature (32). Participants reported not experiencing any difficulties with the management of the application or reading the questions and statements on the smartphone. It thus seemed that filling in the ESM application was acceptable and usable. Another possible explanation could be technological difficulties. Only 7 participants experienced technical issues, mostly related to the operating system of their smartphones. Some operating systems hinder the signals of certain applications to maintain a longer-lasting battery level. For 5 participants, the issues could not be solved during and after the participation period. Solving technical problems was problematic due to the use of telephone contact and the distance between the participants and the research team. Therefore, if a participant experienced a technical problem, there is a great chance that the problems will remain unsolved. Overall, these results are indicating a favorable general and user-friendliness evaluation, that ESM might be feasible for patients with a secondary chronic pain syndrome.

Missing values might be missing (completely) at random and missing not at random (38, 40). To study the reasons for missingness, a binary logistic regression analysis was performed, but no pattern could be detected in the missing data. As a result of this analysis, we may conclude that our missing values are missing at random (40). However, we also observed that the earliest and the latest beep signals were the least filled in, 6.95% and 9.49% respectively, see Figure 4. The beep signals were planned according to a time-contingent, daily random scheme. A time window varying from 15 to 90 min was planned between each beep signal. Nonetheless, the first beep was between 7.30 AM and 9.00 AM, and the last beep (number 10) was between 9.00 PM and 10.30 PM, see also Figure 1. This finding could indicate that there are differences in biological wake-sleep rhythm among chronic pain participants, independently of work state (46). This may have implications for future studies in which ESM beep schemes will be used in chronic pain participants. Our results imply that this wake–sleep rhythm needs to be taken into account, e.g., the first beep a little later on the day, 8.30 AM–9.00 AM instead of 7.30 AM–9.00 AM.

There are some strengths and limitations accompanying this study. First, we will discuss the strengths. This is the first study investigating the acceptability, usability, and feasibility of ESM in secondary chronic pain syndromes. Moreover, our results are indicating that ESM could safely be used in secondary chronic pain syndromes. Regarding ESM itself, ESM seems to be less time-consuming. The response time on each beep signal was on average 87 s. In addition, participants reported not experiencing any difficulties related to ESM, indicating that ESM is easily manageable. Moreover, participants mentioned that ESM did not affect their mood, daily activities, and social contacts. It seems that participants are not adapting their daily and social activities to the use of ESM. A couple of limitations will also be discussed. Although, more than 7/10 beep signals were reported to be feasible (29), however, a low response rate is present in our data. Questions in an electronic diary should be brief. In our opinion, reducing the amount of beep signals could be more feasible, probably resulting in a higher response rate. However, crucial information about what happens between beep signals will be lost. As next, only 19 of the included 34 participants filled in the acceptability and usability questionnaire. This could indicate that a certain group of participants were motivated and probably experienced less problems with ESM, creating a selection bias among participants itself. Sending all participants, a paper version of the acceptability and usability questionnaire, could be a future solution to avoid a number of missing questionnaires and data. As last, another solution could be to solve technical issues faster, which is discussed earlier, such as solving technical issues physically rather than at a distance, or to offering a chatbot.

In conclusion, ESM is a promising measurement tool to help patients and healthcare professionals to gain more insight into daily fluctuations of pain and possible associations with pain-related thoughts, emotions, activities, and environmental factors for primary and secondary chronic pain syndromes, by offering visualizations of the complex disease-related dynamics for patients and healthcare professionals. Measuring the acceptability and usability revealed favorable and encouraging outcomes, with generally satisfied participants.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Medical Ethical Committee of Zuyderland Medical Center (METCZ20210022). The patients/participants provided their written informed consent to participate in this study.

AK and JV contributed to conception and design of the study. AD, JH, MH, AK, CF, and JV wrote the first draft and sections of the manuscript. AD organized the database and performed the statistical analysis. All authors contributed to the article and approved the submitted version.

The present study was funded by the Prinses Beatrix Spierfonds [grant number W.OK17-09].

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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