A Reevaluation of the Simplified Psoriasis Index (SPI) Using the Thai Language Version: A Study Examining the Validity, Reliability, and Interpretability of SPI When Used in Translation

Abstract

Background: The Simplified Psoriasis Index (SPI) is a summary measure of psoriasis for current severity (SPI-s), psychosocial impact (SPI-p), and past history and interventions (SPI-i). Two complementary versions are available, differing only in that current severity is either professionally (proSPI-s) or patient self-assessed (saSPI-s). They have been shown to be valid, reliable, and interpretable. Objective: The current study investigated whether the validity, reliability, and interpretability of SPI could be replicated in an independent study in a different population and setting. Methods: A validated translation of SPI into Thai was used to assess the validity and reliability of SPI for assessing psoriasis in 100 Thai patients. The interpretability of proSPI-s and saSPI-s was assessed in 289 Thai patients. Results: There were close correlations between Psoriasis Area and Severity Index (PASI) and proSPI-s ( r = 0.84) and between PASI and saSPI-s ( r = 0.78). The SPI-p was closely correlated with the validated Thai version of the Dermatology Life Quality Index ( r = 0.78). Excellent intrarater (proSPI-s, saSPI-s, SPI-p, and SPI-i) reliability was demonstrated (all ICC ≥0.88). The PASI-equivalent cutoff scores for mild (PASI < 10) and severe psoriasis (PASI ≥ 20) were <9 and ≥18 for proSPI-s and <11 and ≥20 for saSPI-s. Conclusion: Our study confirms that SPI retains good validity and reliability in translation. The cutoff points we obtained were very close to those of the original study and confirmed that the originally proposed PASI-equivalent cutoff scores for mild and severe psoriasis of <9 and ≥18 for psoSPI-s and <10 and ≥20 for saSPI-s, respectively, were valid for use in a very different language and setting.

Secukinumab efficacy in reducing the severity and the psychosocial impact of moderate‐to‐severe psoriasis as assessed by the Simplified Psoriasis Index: results from the IPSI‐PSO study

“…The current severity domain (SPI‐s) accords extra weight to certain functionally or psychosocially important body sites (scalp, face, anogenital area, hands, feet, with nail psoriasis contributing to scores for the latter two sites if appropriate). Good correlation between PASI and both versions of SPI‐s and between DLQI and SPI‐p was demonstrated in a study of 100 psoriasis patients using the original English version of SPI, 10 and, more recently, in a study using a version translated into Thai 11 . A further study by the same investigators confirmed the responsiveness of SPI‐s to change 12 …”

“…The Simplified Psoriasis Index (SPI), recently developed in Britain, is a holistic psoriasis assessment instrument which incorporates separate domains for current severity (SPI‐s), psychosocial impact (SPI‐p) and past history and interventions (SPI‐i), as shown in Fig. 1 10,11 . It is available in complementary versions either for completion by healthcare professionals (proSPI) or for self‐assessment by patients (saSPI); the only difference between the two is that technical language is avoided in the latter.…”

Factors Influencing Willingness to Pay for Teledermatology among Patients with Psoriasis

“…Patients with a Self-Administered Simplified Psoriasis Index severity score of < 10 and ≥ 20 were defined as having mild and severe psoriasis, respectively. 14 In the case of patients who indicated a WTP for TD, they were asked to select 1 of 4 possible out-of-pocket costs that they would be willing to pay for the TD service: 200 Baht ($6, €5.40); 300 Baht ($9, €8.10); 400 Baht ($12, €10.80); and 500 Baht ($15, €13.50). Biding format was not used in this study.…”

Using the patient‐acceptable symptom state to evaluate patients' perspectives of living with psoriasis: A cross‐sectional study

“…Mild disease severity was signified by saSPI‐s scores <10, while severe disease severity was indicated by scores ≥20. The validated Thai version of saSPI‐s was used 16 …”