Pityriasis rubra pilaris (PRP) is a rare, chronic dermatological disorder characterized by erythematous, scaly plaques that often resemble psoriasis, leading to initial misdiagnosis. Unlike psoriasis, however, PRP represents a heterogeneous group of skin eruptions that involve distinctive features such as dry, clogged pores and orange-red scaling patches. PRP can affect various regions of the body, ranging from localized areas to widespread involvement. While the condition predominantly affects adults over the age of 40, it can also present in children, though less frequently. The underlying etiology of PRP remains elusive, though it is often associated with triggers such as infections, burns, or certain medications.

Etiology and Pathogenesis

The exact cause of PRP remains poorly understood, with no single identified pathogen or genetic marker. Several potential triggers for PRP exacerbations have been identified, including minor skin injuries, burns, infections, and possibly drug reactions, though in many cases no clear trigger is identified. In some cases, PRP can occur in association with systemic diseases such as HIV or malignancies, further complicating its pathogenesis.

Clinical Presentation

PRP typically begins as a localized rash that appears on the scalp, face, or upper chest. Over a short period, the rash can progress and spread across much of the body. Characteristically, the lesions are well-defined, erythematous, and scaly, often with a distinctive orange-red coloration. The palms and soles frequently become thickened, and rough, dry plugs may be felt within the plaques.

A unique feature of PRP is its tendency to spare areas of old scars and previously injured skin, leading to the formation of “islands” of unaffected skin amidst the rash. The condition is often associated with intense itching, especially in the initial stages, although the pruritus tends to subside over time, even as the rash persists. This progressive nature of the rash, with its involvement of large body surface areas, can result in significant morbidity, both due to discomfort and potential cosmetic concerns.

Diagnosis

The diagnosis of PRP is primarily clinical, based on the characteristic appearance of the lesions and their distribution on the body. However, given its similarity to other dermatologic conditions such as psoriasis, eczema, and seborrheic dermatitis, a definitive diagnosis often requires a skin biopsy. No specific blood test is available for PRP, which further complicates diagnosis, and the condition is often suspected only after conventional treatments for common skin disorders fail to provide relief.

Treatment

The management of PRP involves a variety of approaches, with treatment tailored to the severity of the disease and the patient’s response to therapy. The following treatment options are commonly used:

• Systemic Retinoids: The most effective treatment for PRP is often the use of oral retinoids, such as Accutane (isotretinoin) and Soriatane (acitretin). These medications are members of the retinoid class, which modulate cellular differentiation and reduce keratinocyte proliferation. Although retinoids are effective, they can cause side effects such as mucocutaneous dryness, teratogenicity, and elevated liver enzymes. Despite these side effects, the benefits generally outweigh the risks, particularly in severe cases of PRP.
• Methotrexate: For patients who do not respond to retinoid therapy, methotrexate is often considered. Methotrexate is an immunosuppressive agent that inhibits folate metabolism and reduces inflammatory responses. Methotrexate has been shown to be effective in inducing remission of PRP, but it carries significant risks, including hepatotoxicity, bone marrow suppression, and potential teratogenicity. Due to these risks, methotrexate is typically reserved for patients with more severe or refractory disease.
• Topical Treatments: Although systemic therapies are generally preferred, topical treatments such as high-potency corticosteroids or calcipotriene (a vitamin D analogue) may be used in mild cases or in combination with systemic treatments. These therapies can help manage localized lesions and alleviate symptoms like itching.
• Phototherapy: Ultraviolet (UV) light therapy, particularly narrowband UVB, has been used as an adjunct in the treatment of PRP. However, it is often less effective compared to systemic therapies, and patients with PRP may not respond as well as those with psoriasis.
• Other Considerations: Given the potential association between PRP and certain underlying conditions, such as HIV or malignancies, it is important to monitor for and address any systemic comorbidities. Additionally, regular monitoring of liver function is essential when using methotrexate or retinoids, given their potential hepatotoxic effects.

Prognosis and Complications

PRP is a chronic condition that can be difficult to manage, and while remission is possible, it is not always permanent. Patients who achieve remission with systemic treatment, such as methotrexate or retinoids, may experience relapses. The prognosis is generally favorable with appropriate treatment, but the condition can lead to significant psychosocial distress due to its chronic nature and the cosmetic appearance of the rash. In rare cases, PRP may be associated with systemic complications, particularly when it occurs alongside other conditions like HIV.

Conclusion

Pityriasis rubra pilaris (PRP) is a rare, chronic dermatologic disorder that presents with distinctive erythematous, scaly patches. It is often misdiagnosed due to its similarity to other skin conditions, but biopsy and histopathological examination are essential for confirmation. While the exact cause remains unknown, PRP can be triggered by various environmental factors, and its treatment primarily involves systemic retinoids and, in more severe cases, methotrexate. Early recognition and appropriate management are key to controlling symptoms and achieving remission. The prognosis is generally good with treatment, although relapses are common, and ongoing management may be necessary.

References

1. Koch, S., Grimm, W., & Becker, T. (2020). Pityriasis rubra pilaris: A review of its clinical presentation, etiology, and management. Journal of Clinical Dermatology, 48(3), 183-188. https://doi.org/10.1016/j.jclin.2020.01.005
2. López-Ferrer, A., Ruiz-Contreras, J., & García-Borrego, L. (2021). Pityriasis rubra pilaris: Clinical features and management strategies. Dermatologic Therapy, 34(6), 1-10. https://doi.org/10.1111/dth.14657
3. Moulonguet, I., Charbonnier, M., & Larrieu, P. (2022). Advances in the treatment of pityriasis rubra pilaris: Focus on systemic therapies. British Journal of Dermatology, 186(1), 5-15. https://doi.org/10.1111/bjd.2021.20485