Evaluation of Psoriasis Area and Severity Index Thresholds as Proxies for Systemic Inflammation on an Individual Patient Level.

Background: Psoriasis is a chronic and systemic inflammatory disease with a loss of up to 5 life years, which is thought to be reduced by biologic treatment. Disease severity and eligibility for systemic treatment are often based on the cutaneous psoriasis area and severity index (PASI) with a cut-off of 10 in several European countries. However, it is unclear how well this cut-off reflects systemic inflammation and, consequently, the risk for the development of comorbidity.

Objectives: (1) To assess whether specific PASI thresholds, in particular PASI 10, predict elevated biomarkers of systemic inflammation and cardiovascular risk on an individual patient level. (2) To assess the association of PASI and psoriatic arthritis with biomarkers of systemic inflammation and cardiovascular risk.

Methods: Retrospective cross-sectional study of 72 psoriasis patients without systemic treatment.

Results: Overall, 68, 42, and 50% of patients had cardiovascular risk level neutrophil-to-lymphocyte ratio (NLR), C-reactive protein, and elevated platelet-to-lymphocyte ratio (PLR) values, respectively. The respective positive predictive values of PASI 10 were 70, 45, and 70. The performance of the optimal PASI cut-offs according to the Youden index was similarly weak. Subgrouping of patients with a PASI below 10 did not result in a considerably improved reflection of systemic inflammation. PLR was significantly higher in patients with moderate-to-severe compared to mild psoriasis and significantly correlated with PASI in patients with a PASI above 2 (rs = 0.266, n = 64). NLR was significantly higher in patients with psoriatic arthritis.

Conclusion: Specific PASI thresholds were not well suited to predict elevated biomarkers of systemic inflammation and cardiovascular risk on an individual patient level. Therefore, PASI, and possibly other purely cutaneous measures, may not be ideal as stand-alone parameters to define disease severity and eligibility for systemic treatment. Our results are relevant for the ongoing discussion on the definition of psoriasis severity and eligibility for systemic treatment. Further research addressing the added value of a set of biomarkers of systemic inflammation in the assessment of psoriasis severity would be desirable.