Pityriasis rubra pilaris
Published Web Locationhttps://doi.org/10.5070/D36nk505js
Pityriasis rubra pilarisThe Ronald O. Perelman Department of Dermatology, New York University School of Medicine, New York, New York
Marie Leger MD PhD, Tracey Newlove MD, Maria Robinson MD, Rishi Patel MD, Shane Meehan MD, Sarika Ramachandran MD
Dermatology Online Journal 18 (12): 14
Pityriasis rubra pilaris (PRP) is an inflammatory condition of uncertain etiology. We present a case of PRP that demonstrates acantholysis on histopathologic examination, which is a characteristic feature that increasingly is recognized to aid in the diagnosis. We also review the clinical presentations and treatment options for this condition.
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A 58-year-old woman presented to the Charles C. Harris Skin and Cancer Pavilion with a one-month history of a pruritic eruption that started on her scalp. A few days later, the eruption spread to her trunk, and she visited the emergency room. The patient was given hydroxyzine and a prednisone taper. After finishing the taper, new lesions continued to develop on her legs. She reported the occasional use of ibuprofen and trileptal for headaches. The patient reported joint pain in her shoulders and hips several months prior that were not associated with activity or time of day but no other associated symptoms.
There were numerous, edematous, confluent plaques with scale that were distributed on the forehead, infraorbital areas, lateral aspects of the cheeks, perioral areas, back, chest, abdomen, mons pubis, medial aspects of the thighs, buttocks, arms, and legs. There were islands of normal skin on her arms, flanks, and thighs. The palms demonstrated waxy, orange, hyperkeratotic plaques.
A complete blood count and comprehensive metabolic panel were normal. An antinuclear antibody titer was positive with a titer of 1:80 with a speckled pattern. The rheumatoid factor was 7, an erythrocyte sedimentation rate was 32, and a C-reactive protein was 0.9.
There is slight acanthosis and subtle spongiosis. There is overlying parakeratosis and compact orthokeratosis. There is a perivascular lymphocytic infiltrate with dilated thin-walled blood vessels in the papillary dermis. A PAS-D stain fails to reveal a thickened basement membrane or evidence of fungi.
Pityriasis rubra pilaris (PRP) is an inflammatory condition of uncertain etiology. It was first described by the Parisian dermatologist Alphonse Devergie, who called the entity pityriasis pilaris in 1856 .
Five subtypes historically have been described. Type I (50%), or classic PRP, occurs in adults. It is comprised of widespread, follicular papules and plaques and tends to clear spontaneously in 80 percent of patients in one to three years. Type II (5%), which is the atypical adult subtype, tends to be more chronic and presents with areas of alopecia, eczematous patches, and a palmoplantar keratoderma. Type III (10%), which is the classical juvenile type, is similar clinically to type I but occurs in children and tends to remit in one year. Type IV (25%), which is the circumscribed, juvenile subtype, presents with sharply-demarcated areas of follicular hyperkeratosis and erythema of the elbows and knees. Type V (5%) is a familial subtype with an autosomal dominant inheritance pattern that presents in the first few years of life [1, 2]. In adults, the eruption tends to spread caudally, whereas in children it often starts on the lower one-half of the body. More recently, a human immunodeficiency virus (HIV)-associated subtype has been described that presents with follicular keratoses and spicules and that has been described in association with acne conglobata, hidradenitis suppurativa, and lichen spinulosus [3, 4, 5].
Histopathologic features of PRP include alternating checker board orthokeratosis and parakeratosis, psoriasiform hyperplasia, and focal or confluent hypergranulosis. There often are plugs of the hair follicles and shoulder parakeratosis, which is parakeratosis adjacent to the plugged follicle. A mild, superficial, perivascular, lymphocytic infiltrate may be present . A previous biopsy specimen of our patient obtained by an outside dermatologist showed a psoriasiform dermatitis, focal acantholytic dyskeratosis, and spongiosis. Whereas acantholysis has not been considered to be a key histopathologic feature of PRP, multiple case reports and series recently have described this finding [6, 7, 8]. The acantholysis may resemble that found in keratosis follicularis, familial benign chronic premphigus, or pemphigus vulgaris and has a negative direct immunofluorescence pattern . One recent case series described several patients with isolated lesions on the trunk that appeared prior to the development of the characteristic erythroderma with islands of sparing. This led the authors to suggest that acantholysis can be used as a clue to diagnosing PRP when early, isolated papulosquamous lesions are biopsied prior to the development of erythroderma .
Treatment of PRP can be difficult, and no standardized approach has been established, although systemic retinoids are considered first-line therapy [1, 9, 10]. Cyclosporin, methotrexate, and azathioprine are alternatives [11, 12]. There also are reports of successful treatment with infliximab, etanercept [13, 14, 15, 16], and ustekinumab . Patients with HIV may improve with initiation of antiviral therapy 
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