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Pityriasis rubra pilaris
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
Pityriasis rubra pilaris (PRP) is a rare, papulosquamous disorder with a variable presentation and course. It is characterized by follicular hyperkeratotic papules and coalescing salmon-colored plaques with ‘islands of sparing’ that can progress to erythroderma. It is also commonly associated with an orange–red waxy keratoderma. PRP can be divided into six subtypes based on age of onset, morphologic phenotype, and the presence of HIV infection:
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Type I: classical adult
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Type II: atypical adult
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Type III: classical juvenile
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Type IV: circumscribed juvenile
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Type V: atypical juvenile
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Type VI: HIV-associated
Type I (classical adult) PRP is the most common form of the disease (>50% of all cases) and presents with rapid-onset erythroderma, diffuse scale, and keratoderma. Patients with types I and III PRP usually experience spontaneous remission within 1–3 years, while the other types demonstrate a variable or chronic course.
While PRP is typically an idiopathic disorder, it has also been reported in association with various drugs, infections, malignancies, autoimmune diseases, skin trauma, and ultraviolet (UV) exposure. In addition, there are reports of familial cases most commonly associated with mutations in CARD14 .
Given the rarity of the condition, there are no randomized controlled trials assessing treatment efficacy in PRP. Furthermore, it is often unclear whether clinical improvement represents real treatment efficacy or spontaneous remission of the disease. Treatment recommendations are based on case reports and small case series. Recently, multiple robust systematic reviews have been published evaluating the various systemic therapies used to treat this disease.
Management Strategy
Topical therapies mainly serve as adjuncts to systemic treatment for PRP. Emollient use should be encouraged in combination with keratolytics . Topical steroids may reduce pruritus but are often ineffective. Additional topical treatments to be considered include retinoids , vitamin D analogs , and calcineurin inhibitors .
There are a few case reports of the effective use of both narrowband UVB and psoralen and ultraviolet A (PUVA) for PRP. However, given there are also reported cases of UV-induced worsening or onset of PRP, phototherapy should be used cautiously and only when other treatments are contraindicated. Pretreatment phototesting is recommended.
Oral retinoids are considered the first-line treatment for most forms of PRP. In a recent systematic review, significantly higher rates of excellent response were observed with isotretinoin and alitretinoin compared with acitretin. The considerably shorter half-life of the former two drugs (5 weeks) compared to acitretin (3 years) should also be considered when selecting a systemic retinoid.
It is recommended to initiate treatment with isotretinoin at 0.5–2 mg/kg daily for rapid improvement, and then add a second agent if intolerable side effects ensue or if the response is inadequate.
Methotrexate has been reported in several case series as being effective in type I PRP. The long-term efficacy of methotrexate is well established. The reported effective doses range from 10 to 25 mg weekly, but in some patients, higher doses may be necessary. Despite concerns for hepatotoxicity, the concomitant use of methotrexate and retinoids has been reported as a safe combination.
Due to their clinical similarity and evidence of shared immune pathogenesis, targeted treatments for psoriasis have been tested in patients with PRP. Multiple systematic reviews and case reports have demonstrated the successful use of biologics and small molecule inhibitors in treating PRP, including tumor necrosis factor-alpha ( TNF-α) inhibitors , ustekinumab , secukinumab , ixekizumab, brodalumab , guselkumab , and apremilast .
Type VI PRP may respond to antiretroviral therapy . The response appears to correlate with a reduction in viral load.
There is anecdotal evidence (mostly isolated case reports) detailing the successful use of the following in PRP: intravenous immunoglobulin, extracorporeal photochemotherapy, azathioprine, mycophenolate, fumarates, penicillins, and pulsed dye laser.
Specific Investigations
Histology of the affected skin can be useful in aiding the diagnosis. Routine blood tests are recommended as markers of general health and as screening for the use of systemic agents.
An HIV test should be done in all patients. Furthermore, if any suspicion exists, it may be necessary to obtain peripheral blood flow cytometry to rule out cutaneous T-cell lymphoma.
Systematic Reviews
Systemic therapies of pityriasis rubra pilaris: a systematic review
Kromer C, Sabat R, Celis D, et al. J Dtsch Dermatol Ges 2019; 17: 243–59.
In this systematic review of 182 studies reporting on 475 patients, an excellent response was achieved in 42% of patients treated with retinoids, 33% treated with methotrexate, and 51% treated with biologics. Considering multiple factors, including effectiveness, safety, and costs, the investigators suggest starting with isotretinoin as first line, methotrexate as second line, and biologics as third line.
Treatment of pityriasis rubra pilaris type I: a systematic review
Engelmann C, Elsner P, Miguel D. Eur J Dermatol 2019; 29: 524–37.
In this systematic review of 105 studies documenting therapies for type I PRP, the authors suggest first-line treatment with a systemic retinoid; second-line treatment with a combination of retinoid and methotrexate, azathioprine, or ciclosporin; and third-line treatment with biologics, in addition to continuous topical treatment and phototherapy when appropriate.
Pityriasis rubra pilaris response to 13-cis-retinoic acid (isotretinoin)
Goldsmith LA, Weinrich AE, Shupack J. J Am Acad Dermatol 1982; 6: 710–5.
In this prospective, single-arm, non-blinded study, 28 of 45 patients (62%) treated with isotretinoin had marked improvement within 4 weeks, and all 34 patients who returned for follow-up showed marked improvement after 16 weeks of treatment.
The publications above support the use of isotretinoin in doses of 0.5–2 mg/kg daily. Additional options for systemic retinoid therapy include alitretinoin, etretinate, and acitretin.
Methotrexate treatment for pityriasis rubra pilaris: a case series and literature review
Koch L, Schöffl C, Aberer W, et al. Acta Derm Venereol 2018; 98: 501–5.
In this review of 116 patients treated with methotrexate, the overall response rate was 65.5%, with complete clearing in 23.3% and excellent improvement in 17.2%. The doses most commonly administered were between 15 and 25 mg weekly, and doses higher than 25 mg weekly did not show any trend toward a better outcome.
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