Background
Patients with moderate-to-severe psoriasis are candidates for systemic treatment, but it is unknown how many receive such therapy at a national level in Denmark.

Objectives
We aimed to determine the prevalence of conventional systemic therapy use in patients with moderate-to-severe psoriasis and, further, to investigate the time to discontinuation of conventional systemic therapy and initiation of biological therapy among biologic-naïve patients.

Methods
This registry-based study identified a cohort of patients with psoriasis in Denmark. We estimated the prevalence of moderate-to-severe psoriasis at a national level using registry data. Inverse probability weighting was used to mitigate potential selection bias in the prevalence estimate of moderate-to-severe psoriasis. Analyses were then performed on the weighted cohort.

Results
Of patients with psoriasis in Denmark, 10.9% were estimated to have moderate-to-severe psoriasis, of whom 62.3% received either conventional systemic or biological therapy, meaning 37.7% who were considered candidates for systemic therapy did not receive any systemic treatment. The study demonstrated that, comparing previous time periods with more recent years: (i) time on conventional systemic therapy for patients with moderate-to-severe psoriasis has become shorter, with a median (interquartile range) of 3.0 years (0.6–10.0) in 1985–1994 vs. 0.6 years (0.3–2.0) in 2014–2018; (ii) more patients initiated biologics as second-line therapy, with 69.5% in 2010–2013 vs. 71.2% in 2014–2018; and (iii) the median time from initiation of systemic therapy to initiation of biological therapy decreased from 13.3 years (11.5–16.8) in 2010–2013 to 1.9 years (1.7–2.4) in 2014–2018.

Conclusions
This study found that nearly 37.7% of Danish patients with moderate-to-severe psoriasis do not receive systemic treatment even though they would qualify for this. Furthermore, for patients treated with conventional systemics, drug survival decreased during the observation period.