A modern approach to the differential diagnosis of erythrodermic pityriasis rubra pilaris: a retrospective study at V.A. Rakhmanov Clinic of Skin and Venereal Diseases. Part 1

BACKGROUND: Pityriasis rubra pilaris (Devergie disease) is a rare chronic inflammatory skin disease classified as papulosquamous dermatosis. Despite the pathognomonic clinical and pathomorphological signs, diagnosing erythrodermic pityriasis rubra pilaris can be difficult because clinical signs such as diffuse erythema and scaling affecting more than 80% of the body surface area can also be observed in other dermatoses, including psoriasis and cutaneous T-cell lymphoma (mycosis fungoides). AIM: The work aimed to assess the clinical, anamnestic, histological, and immunohistochemical signs of erythrodermic pityriasis rubra pilaris and perform a differential diagnosis with psoriasis and mycosis fungoides. METHODS: A retrospective analysis of medical history, clinical manifestations, and laboratory parameters was performed in 147 patients with erythroderma admitted to the V.A. Rakhmanov Clinic of Skin and Venereal Diseases, University Clinical Hospital No. 2, Sechenov University, in 2014–2024. Of these, 17 (11.6%) patients had erythrodermic pityriasis rubra pilaris. For differential diagnosis, the study included 26 (17.7%) patients with mycosis fungoides and 104 (70.7%) patients with psoriatic erythroderma. Skin biopsies were performed, followed by histological, immunohistochemical, and molecular biological tests (as needed). RESULTS: At admission, the diagnosis of pityriasis rubra pilaris was made based on clinical signs and medical history in 64.7% of patients (n = 11), with histological confirmation in 52.9% of cases (n = 9). In patients with nonspecific histological signs, repeated skin biopsies from several sites were performed to verify the diagnosis. Immunohistochemical and molecular biological tests were used to rule out mycosis fungoides. The clinical and histological signs of erythroderma can be nonspecific, necessitating a comprehensive diagnostic approach. Therefore, the medical history, clinical manifestations, and laboratory and imaging findings must be considered and compared. Moreover, it is essential to rule out mycosis fungoides, a particularly aggressive disease. CONCLUSION: The findings highlight the need for differential diagnosis algorithms for disorders associated with erythroderma.