Pityriasis rubra pilaris: a new proposed classification

Area of Science:

• Dermatology
• Clinical Classification
• Histopathology

Background:

• Pityriasis rubra pilaris (PRP) is a rare chronic skin disorder.
• Previous classifications lacked clarity for certain clinical presentations.
• A need existed for a refined classification system for PRP.

Purpose of the Study:

• To establish a new clinical classification for pityriasis rubra pilaris (PRP) based on a large case series.
• To evaluate the diagnostic utility of the proposed classification, particularly in cases lacking typical histopathological findings.
• To observe the progression of PRP subtypes over time.

Main Methods:

• Clinical data from 168 patients with PRP were analyzed.
• Patients were categorized into four distinct clinical types (I-IV) based on lesion morphology and distribution.
• Histopathological examination was performed, with particular attention to follicular plugging and parakeratosis.
• Longitudinal follow-up data were collected to assess disease progression.

Main Results:

• Four clinical types of PRP were defined: Type I (palmoplantar plaques), Type II (circumscribed elbow/knee patches), Type III (trunk patches), and Type IV (exfoliative erythroderma with follicular plugging).
• Palmoplantar plaques were present in most cases across types I and II.
• Follicular plugging and focal parakeratosis were characteristic histopathological findings, though absent in Type I.
• Disease progression between types was observed in several patients.
• Associated conditions included localized pustular psoriasis and ovarian adenocarcinoma in specific PRP types.

Conclusions:

• The proposed four-type clinical classification of pityriasis rubra pilaris (PRP) effectively categorizes patients.
• This classification aids in recognizing PRP, even in the absence of characteristic histopathological features like follicular plugging.
• The classification provides a framework for understanding disease progression and associated comorbidities.