OBJECTIVES: The objective of this study is to evaluate the relationship between psoriasis severity, as measured by the affected body surface area (BSA), and the initiation of systemic therapy.

METHODS: Adult psoriasis patients from the OMNY Health Dermatology Database were indexed at their first BSA measurement with no history of traditional systemic, biologic, or ultraviolet therapy. Patients were followed from index BSA until initiation of systemic therapy or censoring. Patients were characterized at index BSA, and Cox regression with time-varying effects was employed to quantify the effect of BSA on time to initiation of systemic therapy while controlling for patient characteristics.

RESULTS: A total of 4489 patients were included. Age and gender were normally distributed, and 64% of patients had a history of topical therapy. The distribution of BSA at index was skewed (mean: 8.8, median: 4) and ranged from 0 to 96. Follow-up BSA distributions were similar regardless of proximity to systemic therapy initiation. However, univariable Cox regression demonstrated a notable association between BSA categories with values of at least 5 and time to initiation of systemic therapy, which remained after controlling for age, gender, race, region, history of topical therapy, and continuous BSA value at index. Relative to BSA of 0-1, hazard ratio estimates (95% confidence intervals) from the multivariable Cox model were 1.06 (0.95-1.18) for BSA of 2-4, 1.31 (1.16-1.48) for BSA of 5-9, 1.46 (1.28-1.66) for BSA of 10-19, and 1.32 (1.11-1.58) for BSA of 20 or greater. All covariates were also independently associated with time to systemic therapy initiation.

CONCLUSIONS: These results suggest a modest association between affected BSA and the initiation of systemic therapy in psoriasis patients. Further research is needed to understand the potential influence of other variables on this association in the real-world setting.