Epidemiology and clinical features of psoriasis in hard-to-treat body locations: a Chinese nationwide population-based study.

Background: Having psoriasis in hard-to-treat areas, such as the scalp, face, palms, soles, nails, and genitals, can suffer from a reduced quality of life. This study was designed to investigate the prevalence and risk factors of hard-to-treat body locations of psoriasis, and to describe patients' clinical and demographic characteristics, and quality of life impacts.

Methods: We conducted a multicenter observational epidemiological study involving over 1000 hospitals in China, enrolling a total of 7032 psoriasis patients. Groups were compared to patients without involvement of hard-to-treat areas.

Results: The most frequently affected hard-to-treat area was the scalp (60.01%), followed by the face (22.47%), nails (18.87%), palms or soles (18.23%), genitals or vulvas (12.00%), respectively. Among all patients, 70.71%, 36.65%, 16.30%, 6.48% and 1.45% of patients had involvement of ≥ 1, ≥2, ≥ 3, ≥4 or ≥ 5 hard-to-treat areas. There was a male predominance among patients with involvement of at least one hard-to-treat area(P < 0.001). The smoking rate, BMI (body mass index) and psoriasis family history in patients with at least one hard-to-treat area involvement were significantly higher than those in patients without hard-to-treat area involvement (P < 0.001), especially among patients with nail involvement. With regards to current DLQI (dermatology life quality index), satisfactory rate, and current BSA (body surface area), these findings were all significantly different (P < 0.001) when compared to patients without involvement of a hard-to-treat area. Notably, even in mild-to-moderate psoriasis (BSA < 10), 65.10% of patients showed involvement of ≥ 1 hard-to-treat area, with significant impacts on quality of life (DLQI increase, all P < 0.001) and treatment satisfaction (P < 0.001 vs. non-involved).

Conclusion: Psoriasis commonly affects hard-to-treat locations, even in patients with mild to moderate disease (BSA < 10). The disproportionate impact on quality of life (particularly genital/face involvement) and treatment satisfaction underscores the need for: (1) routine assessment of these areas regardless of BSA, and (2) targeted management of modifiable risk factors (smoking, obesity). These findings support incorporating hard-to-treat area evaluation into psoriasis severity assessments and treatment algorithms.