Few validated measures exist to quantify sleep disturbance among patients who have the chronic inflammatory skin condition prurigo nodularis.
The Sleep Disturbance Numerical Rating Scale (SD NRS) was evaluated for its potential to quantify the level of sleep disturbance among persons who have prurigo nodularis, a chronic inflammatory skin condition in which intense itching leads to hard and extremely itchy nodules on the skin.1 Study investigators determined the scale is reliable and valid for clinicians to use in both their daily practice and during clinical trials for patient-reported outcomes (PROs), publishing their findings in Dermatology and Therapy.2
SD NRS scoring ranges from 0 (no sleep loss) to 10 (no sleep). The primary end point of this trial was the Peak Pruritus NRS (PP NRS), with other patient assessments coming through the Average Pruritus NRS (AP NRS), AP Verbal Rating Scale (AP VRS), Peak Pruritus Verbal Rating Scale (PP VRS), Dynamic Pruritus Score (DPS), and Dermatology Life Quality Index (DLQI). Clinicians, meanwhile, used the Investigator Global Assessment (IGA) and a 7-item version of the Prurigo Activity Score (PAS).
Twenty-one patient interviews were conducted, and among them, 19 patients said falling asleep at night was an issue and 18 reported waking at least once every night. Each day these participants completed the SD NRS, first at baseline and then through 4 weeks of follow-up. Their mean age was 53.1 (range, 27-76) years, and 71% were female.
The study authors explained they undertook their analysis of the SD NRS because patients who have prurigo nodularis frequently report sleep disturbances, with data from one study estimating sleep problems to affect more than 40% of patients with prurigo nodularis.
“Test–retest reliability of the SD-NRS was examined using data for ‘stable’ participants with no score change on the PAS item on number of prurigo lesions in a representative area (hereafter “number of lesions”) or the IGA between baseline and week 4 and a score change of ≤1 point on the PP VRS and AP VRS,” they wrote.
Prurigo nodularis was noted to be moderate in 33% of the study population and severe in 48%. All participants reported their daily life was affected from the sleep disturbance they experienced as a result, with 71% placing blame for their poor sleep on the itch they experienced. Fifty percent of patients reported being awake at night for 30 minutes or less and 28%, an hour or more.
Mean (SD) score on the SD NRS was 5.1 (2.7).
For PROs, substantial test-retest reliability of the SD NRS was demonstrated (intraclass correlation coefficient [ICC] = 0.76), per PP VRS average weekly score. When compared with AP VRS average weekly score, however, the test-retest reliability was close to perfect (ICC = 0.87).
For clinician-reported outcomes, the results remained positive, with test-retest reliability coming in at a moderate level (ICC = 0.48 for the PAS and 0.51 for the IGA).
“ICC values were categorized as less than 0 = no agreement, 0-0.20 = slight agreement, 0.21-0.40 = fair agreement, 0.41-0.60 = moderate agreement, 0.61-0.80 = substantial agreement, and 0.81-1.00 = near-perfect agreement,” the authors explained.
In addition, change in the average weekly score on the SD NRS from baseline to week 4 had a strong correlation with changes in several scales:
Moderate correlations, meanwhile, were seen for changes in IGA score (r = 0.53) and DPS score (r = –0.54) and for PAS scores for lesions with excoriations/crusts and healed lesions (r = 0.50-0.51).
“Effect sizes were higher for ‘improved’ (–1.6 to –2.4) than for ‘worsened/no change’ (–0.0 to –0.9),” the investigators wrote.
“The present analysis provides evidence that the SD NRS is a reliable and valid PRO measure that can be used for capturing changes in loss of sleep in prurigo nodularis in daily practice and clinical trials,” they concluded.
Ongoing research is recommended, however, to confirm their findings, with the investigators pointing to a need for phase 3 clinical trial data to confirm the psychometric properties and meaningful thresholds for use of the SD NRS in prurigo nodularis.
1. Prurigo nodularis. Yale Medicine. Accessed July 12, 2023. https://www.yalemedicine.org/conditions/prurigo-nodularis-overview#:~:text=Prurigo%20nodularis%20is%20a%20chronic,and%20rubbing%20of%20the%20skin.
2. Ständer S, Fofana F, Dias-Barbosa, et al. The Sleep Disturbance Numerical Rating Scale: content validity, psychometric validation, and meaningful within-patient change in prurigo nodularis. Dermatol Ther (Heidelb). 2023;13(7):1587-1602. doi:10.1007/s13555-023-00962-8