Actinic Prurigo

Description

Hereditary polymorphic light eruption is a form of photosensitivity found in the American Indians of the central plains of Canada and the United States and in the Indians of Central and South America. The disorder has also been called familial actinic prurigo, solar dermatitis, and hydroa aestivale. In northern latitudes, skin lesions appear on exposed areas early in spring, become severe during the summer, and abate in the fall. Usually the disorder appears in childhood with eczematous crusted eruptions on the face and arms. Fissured, crusted exudative cheilitis develops on the lips, especially the lower lip. The dorsum of the hands, the laterodorsal aspects of the forearms, and the lower half of the arms often show excoriated papular and nodular lesions. Children frequently have complicating pyoderma. Adults usually exhibit an erythematous plaquelike eruption on the face and other exposed areas. The disease is more severe in children than in adults. Glomerulonephritis can follow streptococcal pyoderma (summary by Fusaro and Johnson, 1980).

Clinical Features

Some hours after sun exposure, actinic prurigo patients experience an intense pruritus and develop a dermatosis on the face and exposed areas. Skin signs include erythematous weeping areas, vesicles, papules, nodules, and plaques. Excoriations are common. The lips and conjunctivae are often affected. The skin lesions may extend onto covered areas. In most persons clearing occurs in the winter, but for some the dermatosis persists throughout the year. An exacerbation is experienced by all patients in the summer. Of 128 AP patients reported from Manitoba, 70% had onset before the age of 10 years (Birt and Davis, 1975). In a Saskatchewan series of 93 AP patients, Lane et al. (1992) found that 45% had an age of onset younger than 9 years and 72% had onset before the age of 20 years. Females were twice as likely to be affected as males in the Birt and Davis (1975) study and 3 times as likely to be affected in the study of Lane et al. (1992).

Berth-Jones et al. (1991) reported 18 cases of juvenile spring eruption of the ears: a pruritic, erythematous, papular and vesicular eruption developing on the helix of the ear following sun exposure, especially in boys aged 5 to 12 years (Anderson et al., 1954). They concluded that juvenile spring eruption is a localized form of polymorphic light eruption. They reported a family in which the condition had occurred in a father and 4 sons and pointed to the reports of familial nature of polymorphous light eruption by Jansen (1978) and Ros and Wennersten (1986).

Clinical Management

Affected persons are sensitive to long ultraviolet radiation and therefore do not benefit from conventional sunscreens. Of 46 patients with HPLE, oral beta carotene afforded adequate photoprotection to 33, and 4 additional patients were protected with the combined use of oral and topical agents (Fusaro and Johnson, 1980).

Inheritance

Birt and Davis (1975) suggested that the inheritance pattern of hereditary polymorphic light eruption is autosomal dominant with incomplete penetrance.

Schnell et al. (2000) performed segregation analysis of actinic prurigo in 12 Saskatchewan pedigrees with American Indian ancestry, comprising a total of 1,148 individuals, ascertained through probands with the diagnosis of actinic prurigo. This disorder has a variable age of onset and, therefore, it was necessary to take age at the time of censoring into account in the analysis. However, as these ages in the case of 57% of the unaffected individuals were missing, an algorithm was devised to impute the missing ages from known birth years in the family based on the age differences among relatives and spouses. Using these imputed ages, simple dominant inheritance with incomplete penetrance and a single age of onset distribution was found. The method for imputing the ages at examination was evaluated, as was the correction for ascertainment, by using alternative methods and comparing the results. Regardless of the method used, a dominant mode of inheritance without any multifactorial component remained the best hypothesis.