Dear Editor
Quality of life (QOL) measures can help clinicians understand patients’ experience of disease, judge the effectiveness of care, and facilitate shared decision making1. To be useful in clinical practice, instruments must be simple and quick to complete. The Skindex Mini (SDM), a three-item questionnaire, was derived from a longer previously validated instrument, Skindex-16, to serve this purpose. To date, two studies have demonstrated robust concurrent validity with strong correlations between SDM scores and Skindex-16 scores2,3. In this study, we sought to further examine construct validity and responsiveness of the SDM in a cohort of patients with atopic dermatitis.
As part of routine care, patients with atopic dermatitis (AD) seen by ES in a medical dermatology clinic at Oregon Health & Science University were given a questionnaire during the appointment check-in process. The questionnaire included the SDM, a patient-reported global assessment of severity (PtGA), an itch numerical rating scale (NRS)4, and a question asking if the patient considered their disease well-controlled. ES included the investigator global assessment of severity (IGA). The SDM was completed by 132 AD patients on at least one occasion and 68 patients on two occasions.
To evaluate construct validity, we examined median and interquartile ranges for SDM domain scores across levels of IGA, PtGA, NRS itch, and overall control, and calculated Spearman’s rank correlation coefficients (rs) of SDM scores with each measure. To evaluate responsiveness, the same approach was applied to changes in SDM domain scores across each measure assessed at a subsequent office visit. Correlations were graded as strong, moderate, and weak (rs 0.70–0.89, 0.40–0.69, and 0.10–0.39, respectively)5 (Table 1).
Table 1.
Skindex Mini (SDM) domain scores
| Symptoms | Emotions | Function | ||||
|---|---|---|---|---|---|---|
| Initial scores | ||||||
| Median | IQR | Median | IQR | Median | IQR | |
| IGA | ||||||
| Clear (n=9) | 1 | [1–2] | 1 | [0–1] | 0 | [0–1] |
| Almost Clear (n=13) | 1 | [1–2] | 1 | [0–2] | 1 | [0–2] |
| Mild (n=18) | 2.5 | [1–3] | 1 | [1–1] | 1 | [0–2] |
| Moderate (n=30) | 4 | [3–5] | 3.5 | [2–5] | 2 | [1–4] |
| Severe (n=32) | 5 | [4–6] | 5 | [2.5–6] | 4 | [3–5.5] |
| rs=0.68 | rs=0.60 | rs=0.59 | ||||
| PtGA | ||||||
| Mild (n=57) | 2 | [1–3] | 1 | [0–2] | 1 | [0–2] |
| Moderate (n=38) | 5 | [3–5] | 3 | [2–5] | 3 | [1–4] |
| Severe (n=32) | 5 | [5–6] | 5 | [4–6] | 4.5 | [3.5–6] |
| rs=0.71 | rs=0.68 | rs=0.64 | ||||
| NRS Itch | ||||||
| Mild, <3 (n=39) | 1 | [1–2] | 1 | [0–1] | 0 | [0–2] |
| Moderate, 3–6 (n=50) | 3 | [3–5] | 3 | [1–4] | 2 | [1–4] |
| Severe, 7–10 (n=41) | 5 | [5–6] | 5 | [3–6] | 4 | [4–6] |
| rs=0.87 | rs=0.76 | rs=0.69 | ||||
| Overall AD Control | ||||||
| Yes (n=70) | 2 | [1–3] | 1 | [0–3] | 1 | [0–2] |
| No (n=55) | 5 | [5–6] | 5 | [3–6] | 4 | [3–5] |
| rs=0.73 | rs=0.67 | rs=0.67 | ||||
| Change in scores* | ||||||
| Median Δ | IQR Δ | Median Δ | IQR Δ | Median Δ | IQR Δ | |
| IGA | ||||||
| Improvement (n=14) | 1 | [0–3] | 0.5 | [0–2] | 0 | [0–3] |
| No change (n=31) | 0 | [−1–1] | 0 | [−1–1] | 0 | [0–2] |
| Worsening (n=1) | −2 | −2 | −2 | |||
| rs=0.33 | rs=0.30 | rs=0.16 | ||||
| PtGA | ||||||
| Improvement (n=18) | 2.5 | [1–3] | 2 | [1–3] | 2.5 | [0–4] |
| No change (n=36) | 0 | [0–1] | 0 | [−0.5–1] | 0 | [0–1] |
| Worsening (n=8) | −1 | [−2 −−0.5] | 0 | [−1–1.5] | 1 | [−1.5–2] |
| rs=0.71 | rs=0.48 | rs=0.40 | ||||
| NRS Itch | ||||||
| Improvement (n=36) | 1 | [0–3] | 1 | [0–2] | 2 | [0–3] |
| No change (n=11) | 0 | [0–0] | 0 | [0–0] | 0 | [0–0] |
| Worsening (n=20) | −1 | [−2–0] | −0.5 | [−1.5–1] | 0 | [−1–1] |
| rs=0.83 | rs=0.58 | rs=0.54 | ||||
| Overall AD control | ||||||
| Gained (n=13) | 1 | [1–3] | 3 | [2–3] | 3 | [0–4] |
| No change (n=45) | 0 | [0–1] | 0 | [0–1] | 0 | [0–2] |
| Lost (n=4) | −2.5 | [−4.5−−1.5] | −2 | [−4−−1] | −1.5 | [−4–0.5] |
| rs=0.58 | rs=0.57 | rs=0.41 | ||||
Positive changes in SDM reflect improving quality of life
Investigator global assessment of disease severity (IGA); Patient global assessment of disease severity (PtGA); interquartile range (IQR); numerical rating scale (NRS); Spearman’s rank correlation coefficient (rs); atopic dermatitis (AD)
Consistent with our a priori hypotheses, we found initial SDM scores to have stronger correlations with patient-reported measures (PtGA, NRS itch, and overall) than the clinician’s assessment (IGA). NRS itch ratings had the strongest correlation with symptoms domain scores. SDM scores in all three domains were significantly higher for patients who reported their disease was not well controlled. During follow-up, correlations between changes in SDM domains and changes in patient-reported measures (PtGA, NRS itch, and overall control) ranged from moderate to strong (rs 0.41– 0.83). Correlations between changes in SDM domains and changes in IGA were weak (rs 0.16–0.33). Notably, when no change was observed in IGA, PtGA, NRS itch, and overall control, the median change in SDM scoring was 0 across domains. Overall, SDM scores behaved as we expected. The weak correlation between change in IGA and change in SDM likely reflects a true discordance between patients’ and physicians’ assessments of disease over time.
The psychometric properties of an instrument may vary depending on the type of skin disease under study. These data add to the validation base of the SDM and support its use in routine clinical practice for quickly assessing the health-related quality of life in patients with AD.
Funding sources:
The project described was supported by the National Center for Advancing Translational Sciences, National Institutes of Health, through Grant Award Number UL1TR002369. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Footnotes
IRB approval status: Approved by the institutional review board at Oregon Health & Science University (IRB 19264).
Skindex Mini ©, contact information and permission to use: Mapi Research Trust, Lyon, France, https://eprovide.mapi-trust.org
This manuscript describes original work that was accepted in abstract form for the 2020 Society of Investigative Dermatology Annual Meeting Virtual Conference. The work is not published or submitted elsewhere.
Conflict of Interest: MMC holds a copyright for the Skindex Mini
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