Shades of grey: what is paediatric psoriasiform dermatitis and what does it have in common with childhood psoriasis?

Abstract

While the majority of children with a chronic itchy rash suffer from atopic dermatitis (AD) and other forms of dermatitis, psoriasis is in the differential diagnosis. Certain patterns such as guttate and napkin psoriasis are accepted as classic paediatric psoriasis (PP); however, there are many patients who do not fit these classic forms of PP nor fulfil the accepted criteria for AD. 'Psoriasiform dermatitis' (PD) is a term that has been used for these patients; however, it has not been formally defined. Identification of this group of patients, who although not having the typical clinical features of psoriasis, respond well to psoriasis-specific treatment, may assist treatment decisions for these patients. To describe PD and compare it with typical PP. Patients with classic PP (n=109) were compared with a control group with AD (n=449) and assessed for 21 clinical features associated with PP. Multivariate nonlinear regression analyses determined which features best separated the groups. Patients with dermatitis who demonstrated any of these 21 features (n=43), which were used to diagnose PD, were then compared with the PP and AD groups. They were managed with psoriasis-specific treatment and Psoriasis Area and Severity Index (PASI) was recorded. Of the 21 clinical features, 12 were found to clearly separate the classic PP and AD groups. Using the eight most significant (P<0.0001) features, we found these two groups clearly separated at a score of 3 out of 8. Children with PD with ≥4 of these features responded well to treatment for psoriasis with a mean reduction of PASI by 85% at 6weeks. We found that patients with dermatitis who have ≥4 psoriasis-associated features may have a condition that has been previously alluded to but not defined in the literature, 'psoriasiform dermatitis'. Treatments usually reserved for patients with psoriasis appear to be effective in these patients.