The Psoriasis–Eczema Interface: Clinical Classification and Therapeutic Implications From a Bicentric Experience

BACKGROUND: Psoriasis (PSO) and atopic dermatitis (AD) have long been regarded as distinct entities. However, emerging evidence indicates that they may represent two poles of a shared immunologic spectrum, where Th1/Th17 and Th2 pathways coexist or shift dynamically. The clinical overlap between these diseases, whether spontaneous or biologic-induced, remains poorly characterized. METHODS: We performed a retrospective bicentric study (February 2023-June 2025) at two Italian tertiary centers. Clinical, dermatopathological, and photographic databases were screened with predefined terms. Descriptive analyses summarized characteristics and treatment responses. RESULTS: We included 105 patients: 49 with spontaneous (20 coexisting; 29 overlapping) and 56 with drug-induced conditions (31 anti-IL-17- and 6 anti-TNFα-drug induced eczema; 19 dupilumab-induced PSO). Coexisting cases often combined scalp/elbow PSO with palmoplantar or flexural eczema. Overlapping lesions, frequently on hands/soles, showed mixed histology (spongiosis with acanthosis, hypogranulosis, and Munro microabscesses). For spontaneous forms, Janus kinase (JAK) inhibitors were the most consistently effective treatment, followed by IL-23 inhibitors and methotrexate. After withdrawal of culprit biologics, JAK inhibitors and anti IL-23 agents achieved high control rates of drug-induced eczemas. Dupilumab-induced PSO was mainly in plaques or palmoplantar; about half of the cases were manageable without drug discontinuation. CONCLUSIONS: PSO and AD may represent a continuum spectrum of disease with coexisting or overlapping presentations that influence treatment choices; forms of psoriasis or eczema induced by biological drugs also complicate diagnosis and treatment. JAK inhibitors, targeting shared downstream signaling, represent a rational, effective option at the PSO-AD interface.