THE CLINICAL AND HISTOMORPHOLOGICAL FEATURES OF PITYRIASIS-RUBRA-PILARIS - A COMPARATIVE-ANALYSIS WITH PSORIASIS

Pityriasis rubra pilaris (PRP) is an idiopathic erythematous scaling e ruption which can be difficult to distinguish from psoriasis. We explo red the clinical features, including background medical illnesses and potential triggers in patients with PRP, and also its histomorphologic spectrum. Patients with PRP were selected by natural language search of dermatopathology databases containing 250 000 cases accessioned ove r a 3-year period. A detailed medical history was obtained on each pat ient via office chart review and patient interviews. We compared the h istologic findings in skin biopsies from patients with PRP to those of biopsies matched for site and age from control patients with psoriasi s. Certain aspects of the clinical presentations encountered in the st udy group patients have not been previously emphasized, including erup tions compatible with a vesiculobullous disorder in 4 patients. Severa l patients had evidence of underlying iatrogenic or systemic immune dy sregulatory states and certain triggers could be isolated such as emot ional stress and prior exposure to microbial pathogens. Histomorpholog ic features predictive of PRP included follicular plugging, an increas ed granular cell layer, and acantholysis. While seen in a minority of biopsies of PRP, morphologic discriminators supportive of a diagnosis of psoriasis included neutrophils in the parakeratotic scale crust, an d dermal papillae capillary ectasia with vessels lying in direct appos ition to the epidermis. Other morphologic features were encountered in biopsies of PRP which have received little emphasis in the dermatopat hology literature, including epithelial atrophy, significant dermal in flammation, the presence of eosinophils and plasma cells within the in flammatory infiltrates, an abnormal granular cell layer, and epidermol ytic hyperkeratosis, albeit none were statistically signficant predict ors of PRP over psoriasis. Nevertheless, their identification emphasiz es the varied histologic spectrum of PRP. The almost ubiquitous findin g of acantholysis and the presence of an abnormal granular cell layer in many biopsies of PRP suggests that abnormal keratins or defects in the retinol signalling pathway may be of pathogenetic importance. (C) Munksgaard 1997.