Psoriasis is a common and chronic immune-mediated inflammatory disease of the skin affecting approximately 2% of individuals of European descent with a strong genetic susceptibility.
Classic lesions consist of round, well-circumscribed erythematous plaques covered by a thick silver scale with a predilection for elbows, knees, scalp, lumbosacral and anogenital regions. Fingernail plate involvement includes pitting and distal onycholysis.
Inverse psoriasis ( flexural distribution ), guttate psoriasis, pustular or erythrodermic psoriasis are other clinical variants.
Pityriasis rubra pilaris ( PRP ) is a chronic skin disorder of abnormal keratinization classified by Griffiths into five types based on the age of onset and the clinical features.
Familial pityriasis rubra pilaris belongs to the type V group ( atypical juvenile ) and accounts for about 5% of all cases.
This chronic skin disorder usually presents at birth or appears during early childhood. It is characterized by small keratotic follicular papules forming disseminated salmon-colored scaly plaques that surround islands of normal skin, and diffuse red-orange palmoplantar keratoderma. Lesions typically progress rostral to caudal. While nails can be dystrophic, pitting of nails is not a feature of this disease. Skin biopsies can be performed if the clinical features or the responses to treatment are unusual. Histopathological analysis shows psoriasiform hyperplasia presenting as acanthosis with elongation of the rete ridges, parakeratosis and mononuclear cell infiltrate.
Compared to psoriasis, the epidermal hyperplasia in pityriasis rubra pilaris is more irregular, the granular layer is preserved, follicular plugging is characteristic and neutrophils in the stratum corneum are not essential.
Differential diagnosis of psoriasis includes other papulosquamous disorders. Pityriasis rubra pilaris shows clinical features similar to phrynoderma ( vitamin A deficiency ), psoriasis, erythrokeratodermia and other causes of cornification.
Management of psoriasis includes patient education, topical therapy ( corticosteroids, calcineurin inhibitor, Calcipotriene, emollients, keratolytic agents ), ultraviolet light, and systemic therapy ( retinoids, Methotrexate, Cyclosporine and anti-TNF agents ).
The treatment of pityriasis rubra pilaris is often disappointing. Milder cases of the disease can be treated with emollients, topical corticosteroids, Tazarotene, keratolytic agents or calcineurin inhibitor whereas systemic retinoids and/or TNF-alpha blocking agents are required in severe cases.
The prognosis of both disorders is that of most chronic diseases, with spontaneous remissions and exacerbations. Arthritis is present in about one fourth of psoriasis patients, and there is an increased risk of metabolic syndromes and cardiovascular diseases.
Both phenotypes have been associated to CAspase Recruitment Domain-containing protein 14 ( CARD14 ) mutations. CARD14 is an epidermal regulator of NF-κB transcription factor. Mutations in CARD14 initiate a process that includes inflammatory cell recruitment by keratinocytes and perpetuate a vicious cycle of epidermal inflammation and regeneration that cause the abnormal keratinization. ( Xagena )
Touitou I et al, Orphanet Journal of Rare Diseases 2013, 8:162