Monitoring Chronic Spontaneous Urticaria: Help from an App
—Based on the findings from a recent study, visual analog scales are reliable tools to measure chronic spontaneous urticaria disease activity and can be incorporated into mobile health apps.
For patients who suffer with it, chronic spontaneous urticaria (CSU) can adversely affect many aspects of their lives. As a long-lasting disease with debilitating signs and symptoms, it can have negative effects on quality of life, work and school productivity, and social interactions, making it important to have a way to monitor the course of the disease. The CRUSE mobile app, which was launched in March 2022 and is now available in 16 languages, may be able to aid in this monitoring.1
To look at the accuracy of the CRUSE app, Bernardo Sousa-Pinto, MD, PhD, of the Department of Community Medicine, Information, and Health Decision Sciences, Faculty of Medicine, University of Porto, Portugal, and his colleagues from countries around the world assessed the concurrent validity, intra-rater reliability, test-retest reliability, responsiveness, and minimal important difference (MID) of the visual analog scales (VASs) of the app. Their report was published in Allergy.1
Capturing urticaria and angioedema activity
The 5938 patients who met the study’s inclusion criteria were 18 to 90 years of age and had a self-reported diagnosis of CSU.1 They downloaded the CRUSE app based either on their healthcare provider’s recommendation or found it online themselves.
The CRUSE app has a daily monitoring questionnaire to track patients’ signs and symptoms of CSU and angioedema. The 2 scores included are the urticaria activity score for 7 days (UAS7) and the angioedema activity score (AAS). The app also asks:
- Overall, how much did your urticaria bother you in the last 24 hours?
- How much did your urticaria affect your productivity at school/work today?
- Please indicate how your health is today.
Patients are also questioned about what medications they’re taking each day and, every month, they’re asked to complete the Urticaria Control Test (UCT) and the Angioedema Control Test.
Digital VAS validity and reliability
For concurrent validity (amount of agreement between 2 measures taken at the same time), Dr. Sousa-Pinto and his team found that VAS urticaria was strongly correlated with VAS productivity (correlation coefficient [CC] 0.734, 95% confidence interval [CI] 0.725 to 0.744) and was moderately negatively correlated with VAS EQ-5D (CC -0.560, 95% CI -0.565 to -0.554). The investigators also found that VAS productivity and VAS EQ-5D were moderately negatively correlated (CC -0.53, 95% CI -0.54 to -0.52).
An increase in UAS score was associated with increased VAS urticaria and VAS productivity and with decreased VAS EQ-5D. For each increase of 1 unit in the UAS score, the VAS urticaria rose by 12.5 units on average (95% CI 12.5 to 12.6; r2 0.61), and the VAS productivity increased by 8.8 units on average (95% CI 8.7 to 8.9; r2 0.44). There was less of an association for VAS EQ-5D: An UAS score increase of 1 unit was associated with an average decrease of 6.5 units in the VAS EQ-5D (95% CI -6.6 to -6.5; r2 0.29).
Looking at intra-rater reliability for all VASs, > 75% of the days had no differences in the first and last value recorded on the same day. The differences between the first and last daily values that exceeded the MID were 3.3% for VAS EQ-5D and 7.1% for VAS urticaria. All VASs had very high intra-class CCs (ICCs): 0.950 for VAS urticaria and 0.959 for VAS EQ-5D. ICCs of < 0.5 indicated low reliability (both for test-retest reliability and intra-rater reliability); 0.50 to 0.75 indicated moderate reliability; and > 0.75 indicated high reliability.
Assessment of test-retest reliability showed that the 3 VASs had a high ICC when the UAS7 was used to define clinical stability. For VAS urticaria, looking at the sum of the 7 VASs for the week, the ICC was 0.933 (95% CI 0.925 to 0.941); when looking at the last VAS of the week, the ICC was 0.803 (95% CI 0.781 to 0.822). When the UCT was used to define clinical stability, VAS EQ-5D showed the highest ICC (0.799, 95% CI 0.747 to 0.840), followed by VAS productivity (0.752, 95% CI 0.669 to 0.814) and VAS urticaria (0.644, 95% CI 0.476 to 0.747).
Measuring VAS responsiveness
Responsiveness of each daily monitoring VAS was measured with the UAS7 and the UCT. When the UAS7 was used to define clinical change, large effect sizes were seen for both the sum of the 7 VAS urticaria of the week (Cohen’s effect size 1.06; standardized response mean [SRM] 1.49) and for the last VAS urticaria of the week (Cohen’s effect size 0.79; SRM 0.90). VAS productivity and VAS EQ-5D showed moderate-to-large effect sizes (between 0.67 and 1.18 and between 0.60 and 0.81, respectively).
When the UCT was used to define clinical change, moderate Cohen’s effect sizes were seen for responsiveness of VAS urticaria (0.57; SRM 0.51), whereas small Cohen’s effect sizes were seen for VAS productivity (0.49; SRM 0.47) and VAS EQ-5D (0.35; SRM 0.33).
For the MIDs, distribution-based methods were used, with the MID being 0.5 times the standard deviation of the baseline observations. The MID for VAS urticaria was 17 units (out of 100); for VAS productivity, it was 15 units; and for VAS EQ-5D, it was 11 units.
Limitations and future directions
The investigators mentioned several limitations to their study. First, different time periods were used for the different parameters measured. Additionally, the sample sizes in some cases were smaller than the team would have liked, and the method used for measuring the MID values was not optimal. Lastly, there may have been some selection biases.
In an interview with app, when asked about future research, Dr. Sousa-Pinto said, “Now that we have understood that digital VASs in the CRUSE app are valid instruments to monitor patients with CSU, we would like to conduct studies assessing how patients with CSU behave in terms of medication use patterns and adherence and how this relates to their symptoms; the impact of CSU on quality of life and on work and school productivity; and what are the factors that influence adherence to the CRUSE app.”
"These studies," he says, "will allow treating clinicians to better understand CSU and patients’ behaviors towards this disease in a real-life context."
Dr. Sousa-Pinto also discussed the clinical implications of his team’s study. “Our findings indicate that digital VASs are valid and reliable tools to monitor the symptoms of patients with CSU,” he noted. “These findings support the use of these daily monitoring tools through mobile health apps: in this case, the CRUSE app. With this, patients can register their daily symptoms and medication use between consultations. This allows the physician to have a better understanding of how well the patient has been controlled—with potential implications for treatment adjustment—and the patient can have an increased awareness of his or her disease.”
"Mobile health apps are not one-size-fits-all solutions for the management of patients with chronic diseases," Dr. Sousa-Pinto was quick to add. “However, in some subsets of patients, they can play an important role in disease monitoring,” he says. “Our results support the use of the CRUSE app—which is freely available in a wide set of countries—for the monitoring of CSU.”
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