A Modern Approach to the Differential Diagnosis of Erythrodermic Pityriasis Rubra Pilaris: A Retrospective Study at the V.A. Rakhmanov Clinic of Skin and Venereal Diseases. Part 1

BACKGROUND: Pityriasis Rubra Pilaris (PRP, Devergie's disease) is a rare chronic inflammatory skin disease belonging to the group of papulosquamous dermatoses. Despite the pathognomonic clinical and pathomorphological signs for PRP, diagnosing the erythrodermic form of this disease often becomes challenging, as the clinical picture of diffuse erythema and scaling affecting more than 80% of the skin surface can also be observed in other dermatoses, such as psoriasis and cutaneous T-cell lymphoma (mycosis fungoides).

AIM: To compare and analyze the clinical-anamnestic, histological, and immunohistochemical features of the erythrodermic form of Pityriasis Rubra Pilaris and to perform a differential diagnosis with psoriasis and mycosis fungoides.

METHODS: The study conducted a retrospective analysis of anamnestic data, clinical manifestations, and laboratory parameters of 147 cases of erythroderma among patients hospitalized at the V.A. Rakhmanov Clinic of Skin and Venereal Diseases, University Clinical Hospital No. 2, Sechenov University, in 2014–2024. Inclusion criteria were the presence of informed consent, age over 18 years, and the presence of a disease accompanied by the development of erythroderma (Pityriasis Rubra Pilaris, psoriasis, mycosis fungoides). Skin biopsies were performed on patients, followed by histological, immunohistochemical, and molecular biological studies (if necessary).

RESULTS: According to the retrospective analysis, the study included 17 (11.6%) cases of the erythrodermic form of Pityriasis Rubra Pilaris. For differential diagnosis, 26 (17.7%) patients with mycosis fungoides and 104 (70.7%) patients with psoriatic erythroderma were also included. A diagnosis of Pityriasis Rubra Pilaris was initially established upon admission based on clinical and anamnestic data in 64.7% (n=11) of patients and was histologically confirmed in 52.9% (n=9). In cases with nonspecific histological signs, patients underwent repeated skin biopsies from several sites to verify the diagnosis. Immunohistochemical and molecular biological studies were also performed to rule out mycosis fungoides. Based on the obtained data, it was established that psoriatic erythroderma is not difficult to identify; however, in certain doubtful cases, a differential diagnosis with mycosis fungoides is also necessary.

CONCLUSION: The clinical and histological signs of erythroderma can be nonspecific, emphasizing the importance of a comprehensive approach to diagnosis. Therefore, it is necessary to consider and compare the patient's medical history data, clinical manifestations of the disease, and the results of laboratory and instrumental diagnostics. Particular attention should be paid to ruling out such an aggressive disease as mycosis fungoides. Based on the results obtained, the development of an algorithm for the differential diagnosis of diseases accompanied by erythroderma is highly relevant.