A modern approach to the differential diagnosis of the erythrodermic form of pityriasis rubra pilaris: a retrospective study . Part 2
BACKGROUND: Pityriasis rubra pilaris (PRP, Devergie’s disease) is a rare chronic inflammatory skin disease belonging to the group of papulosquamous dermatoses, clinically characterized by erythematous papules and plaques with frequent development of erythroderma. Erythroderma can also be observed in psoriasis and cutaneous T-cell lymphoma (mycosis fungoides). Based on a previously conducted retrospective clinical and epidemiological study of patients with the erythrodermic form of PRP, psoriasis, and mycosis fungoides for the period 2014–2024 at the V.A. Rakhmanov Clinic of Skin and Venereal Diseases (see Part 1), it can be concluded that these diseases may have similar clinical manifestations. However, the histological signs of erythroderma are often non-specific, which complicates diagnosis verification. Furthermore, when mycosis fungoides is suspected, additional diagnostic methods and the development of a differential diagnostic algorithm for diseases presenting with erythroderma are required. AIM: To conduct a comparative analysis of clinical, anamnestic, histological, and immunohistochemical features of the erythrodermic form of PRP, psoriasis, and mycosis fungoides based on literature data and the results of our study, with the subsequent development of a differential diagnostic algorithm for erythroderma. METHODS: The study involved an analysis of the literature using the PubMed, Scopus, and Google Scholar databases for the period 2000–2025, as well as the results of a clinical and epidemiological study conducted at the V.A. Rakhmanov Clinic of Skin and Venereal Diseases, University Clinical Hospital No. 2, Sechenov University, for the period 2014–2024. RESULTS: According to the literature, erythroderma develops in a significant proportion of patients with PRP, whereas in psoriasis it is observed in 1–2.25% of cases, and in late-stage mycosis fungoides – in 17.3% of patients. PRP is characterized by a bimodal age incidence peak: the first peak occurs in childhood, the second in adulthood. The onset of the disease is usually acute or subacute. The rash typically shows caudal spread with possible spontaneous regression. Key differential diagnostic features of PRP included salmon-colored plaques that coalesce to develop erythroderma, the presence of "islands" of spared skin, palmoplantar keratoderma, and alopecia. It was previously believed that a positive response to systemic retinoids combined with an absent or minimal response to phototherapy could be considered an important clinical diagnostic criterion favoring PRP in the differential diagnosis from psoriasis and mycosis fungoides. However, resistance and insufficient response to systemic retinoid therapy are currently being reported with increasing frequency. CONCLUSION: Differential diagnosis of the erythrodermic form of PRP, psoriasis, and mycosis fungoides requires an integrated approach, based on clinical and anamnestic data analysis and the results of laboratory and instrumental diagnostic methods. The proposed algorithm for the differential diagnosis of diseases presenting with erythroderma serves as a valuable tool for accurate and rapid diagnosis verification and the prompt selection of targeted therapy.