Actinic prurigo and polymorphic light eruption: common pathogenesis and the importance of HLA-DR4/DRB1*0407

Abstract

Actinic prurigo (AP) and polymorphic light eruption (PLE) both belong to the group of idiopathic photodermatoses, but it remains controversial whether AP is a distinct photodermatosis or a variant of PLE. The aim of this study, by collecting data from 119 patients with features of these disorders, was to establish whether specific criteria could be used to distinguish AP from PLE prospectively. We found that presence of the eruption on both exposed and covered sites, its occurrence in winter, persistence of lesions beyond 4 weeks, mucosal and conjunctival involvement, excoriation and scarring of the skin were important features of AP which were not typical of PLE. On this basis, confident clinical diagnoses could be reached in 103 of 119 patients (87%), 57 with AP and 46 with PLE, supported by phototesting and negative lupus serology. HLA typing subsequently confirmed the strong association (90%) between AP and the DR4 allele, in particular with the rare subtype DRB1*0407 which was present in 60% of these patients. No HLA association was found in PLE. In the 16 remaining cases, however, clinical overlap meant that no definite diagnosis could be made; these patients were notionally described as having persistent PLE (PPLE). Demographic and HLA data in this group suggested that PPLE was perhaps most appropriately grouped with PLE. In addition to those patients who were difficult to classify, 35% of our typical AP patients also described clinical progression from PLE to AP, AP to PLE or coexistence of both AP and PLE. In conclusion, our study suggests that while AP and PLE are clinically distinct conditions in most cases, they may perhaps share a common pathophysiological basis. The AP phenotype may be determined by HLA and perhaps other factors in patients otherwise predisposed to PLE.

Photosensitivity disorders in children

“…The onset is usually in childhood, but it ranges from 2 to 43 years. 25 The mean age of onset is \10 years of age in a study from the United Kingdom, 26 and at 4 to 5 years of age in the native Amerindian population. 28 Clinically, AP causes a variety of lesions papules, plaques, and nodules (Fig 4).…”

Fotodermatoses Autoimunes Parte II - Manifestações Clínicas e Terapêutica

“…Considerada inicialmente como uma variante clínica da EPL, 15 o PA é actualmente distinguido como uma entidade clínica específica pelas suas características clínicas únicas e carácter persistente das lesões. 16 Predomina em doentes de fototipos altos (III a V) e é duas vezes mais comum no sexo feminino que no masculino.…”

Fotodermatoses Autoimunes Parte I - Fisiopatologia e Diagnóstico

“…Uma forte associação foi encontrada ente PA e HLA DR4B1*0401 e HLA DRB1*0407, respectivamente em 80% -90% e 60% dos doentes. [34][35][36] Postula-se que estes polimorfismos poderão implicar uma modificação da resposta imunológica a fotoantigénios, contribuindo para o desenvolvimento da doença. 34 A distribuição geográfica destes alelos pode explicar a razão pela qual o PA é mais comum na América do Norte, Central e do Sul, onde a prevalência destes alelos na população é elevada, em comparação com a população caucasiana, na qual a prevalência é baixa (4,4% -6,7% da população).…”