Actinic PrurigoL56.4

Hutchinson 1878; Haxthausen 1918; Fox 1939; Escalona 1959; Lopez-Gonzales 1961;

Rare, chronic, idiopathic photodermatosis leading to scarring, especially in children and adolescents, with the development of prurigo and eczema-like skin changes that occur preferentially in areas exposed to light. Considered by some authors to be a special form of polymorphic light dermatosis . It can severely impair the quality of life

Two forms are distinguished by some authors:

• Non-American actinic prurigo with partial symptoms of atopic dermatitis, polymorphic light dermatosis, hydroa vacciniforme and persistent light reaction.
• American (hereditary) actinic prurigo occurring in Indians in North and Latin America. There it is called "hereditary polymorphic light dermatosis" or "familial actinic prurigo".

More common in indigenous South American populations (prevalence in Mexicans is up to 5% of the population), mestizos and Eskimos; also occurs sporadically in Europe.

The disease is regarded as a variant of polymorphic light dermatosis and thus as a delayed-type hypersensitivity reaction to a photo-induced antigen. Depending on ethnicity, different HLA-restrictions (e.g. HLA-A28, HLA-B39, HLA-DR4) have been observed. The action spectrum for the provocation of pathological skin reactions lies in both the UVB and UVA range with a predominance of UVA.

There is evidence of an abnormal immune response with an increase in ^CD4+Tlymphocytes. The presence of IgE, eosinophils and mast cells indicates that this may be a hypersensitivity reaction.

Immediately after radiation exposure, development of an early urticarial phase. This slowly changes into a persistent, lichenified dermatitis. Subsequently, or overlapping, the typical pruriginous skin changes develop in the light-exposed areas, as well as scattered reactions. Mostly a year-round course with worsening in summer. Conjunctivitis and cheilitis of the lower lip have been described.

Skin biopsies show hyperkeratosis, spongiosis and acanthosis in the epidermis with lymphocytic perivascular infiltration in the dermis. A biopsy of the labial mucosa often shows lymphoid germinal centers in the lamina propria, which can help to differentiate actinic prurigo from polymorphous light dermatosis. Studies have also described an infiltration of eosinophils and mast cells in the underlying mucosa of the affected lesions, which correlates with a delayed type IVb hypersensitivity reaction.

Polymorphic light dermatosis; atopic eczema; porphyria; lupus erythematosus; airborn contact dermatitis; photoallergic eczema or phototoxic dermatitis; chronic actinic dermatitis;

Physical, in particular textile light protection. See below for photoprotective agents.

Topical corticosteroids are helpful in the acute stage.

In severe, therapy-resistant cases, immunosuppressive treatment with azathioprine 100 mg/day or with glucocorticoids such as prednisolone (e.g. Solu-Decortin H) 40-60 mg/day.

Thalidomide 200 mg/day ( off-label use) and cyclosporine (3mg/kgKG) appear to be effective.

Individual case reports have reported good success with baricitinib, a JAK-1/2 inhibitor (4mg/day) and dupilumab (Gli-Lianes J et al. 2024).

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2. Escalona PE, Magana LM (1959) Dermatologfaia: Io esencial para el estudiante, 2nd edn, Mexico, pp. 174-178
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4. Gil-Lianes J et al (2024) Complete response of actinic prurigo to oral baricitinib. JDDG 22: 837-839
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