Background: Psoriasis affects 2-4% of the population, with the most common clinical type being plaque psoriasis. The linear form of psoriasis is very rare. The literature on linear psoriasis (LP) consists of only case reports, and data are few.
Objective: This study aimed to better understand LP in a large-scale study.
Patients and methods: We retrospectively retrieved the medical records from 14 French medical centers of patients newly diagnosed clinically with LP, with or without the support of histology, between 1 February and 31 July 2015. For each case, we assessed the clinical features, treatments and treatment efficacy.
Results: In total, 30 cases of LP (mean age 26.8 years, 13 males) were reported. Mean age at onset of LP was 20.0 years, with 18 developing LP in childhood. Ten patients had a family history of psoriasis, and two had psoriatic arthritis. A total of 19 cases were linear at onset, with concomitant classical psoriasis; these were termed "superimposed" LP. The remaining 11 cases were not associated with classical psoriasis and were termed "isolated" LP. In four of the superimposed cases, LP developed when the patient was receiving systemic treatment: methotrexate (n = 2), etanercept (n = 1) or infliximab (n = 1). Topical steroids were effective in 76% of cases in which they were used, and systemic treatment was effective in < 66%. Treatments were less effective in LP than in classical psoriasis.
Discussion: We identified a wide range of LP, with two profiles: isolated LP and superimposed LP. Topical treatment usually evoked clinical response, with relative resistance to systemic therapy. Methotrexate and anti-tumor necrosis factor (TNF)-α therapies can possibly unmask LP.