Assessing the validity and interpretability of the Simplified Psoriasis Index in Tunisian patients

Introduction: Multiple scores have been developed to assess the severity of psoriasis, but these scores have many limitations. The Simplified Psoriasis Index (SPI) is a summary score with separate components for current severity (SPI-s), psychosocial impact (SPI-p), and past history and interventions (SPI-i). It is available in two similar versions: proSPI and saSPI. Aim: To assess the validity of the SPI by studying its correlation to the benchmark scores in Tunisian patients. Methods: It was a prospective bicentric study including 80 patients with plaque psoriasis. Results: The median PASI was 7.6 and the median DLQI was 9. The median proSPI-s was 6 and the median saSPI-s was 8. The median SPI-p was 7. The median SPI-i was 2. There was a strong correlation between the proSPI-s and PASI (r=0.87) and between the proSPI-s and saSPI-s (r=0.82). There was a medium correlation between saSPI-s and PASI (r=0.70) and between SPI-p and DLQI (r=0.67). The threshold value for proSPI-s and saSPI-s was 7.25. The threshold value for SPI-p was 6.5. Conclusion: The SPI aims to provide a concise but global measure of the severity and impact of psoriasis on quality of life. The use of SPI has several advantages: the simplicity of use, the additional weight given to critical locations of psoriasis, the possibility for the patient to self-assess his own disease, and the possibility of evaluating all the dimensions of psoriasis at the same time.