Epidemiology of psoriasis in hard-to-treat body locations: data from the Danish skin cohort.

Background: Having psoriasis in hard-to-treat areas, i.e. the scalp, face, palms, soles, nails, and genitals, respectively, can impair patients' quality of life. We investigated the prevalence of hard-to-treat body locations of psoriasis, and described patients' clinical and demographic characteristics, and quality of life impacts in a population-based cohort.

Methods: We performed a cross-sectional study using a total of 4016 adults (≥18 years) with psoriasis from the Danish Skin Cohort. Groups were compared to patients without involvement of hard-to-treat areas.

Results: The most frequently affected hard-to-treat area was the scalp (43.0%), followed by the face (29.9%), nails (24.5%), soles (15.6%), genitals (14.1%), and palms (13.7%), respectively. Higher prevalence was generally seen with increasing psoriasis severity. Among all patients 64.8, 42.4, and 21.9% of patients had involvement of ≥1, ≥2, or ≥ 3 hard-to-treat areas. Those with involvement of certain hard-to-treat areas such as hands, feet, and genitals had clinically relevant DLQI impairments. Having involvement of one hard-to-treat area was significantly associated with other hard-to-treat areas affected even after adjusting for age, sex, and psoriasis severity.

Conclusion: Psoriasis commonly affects hard-to-treat locations, even in patients with mild disease. For some of these areas, patient-reported disease burden, e.g. as measured by DLQI, is impaired.