A case of actinic prurigo showing hypersensitivity of skin fibroblasts to ultraviolet A (UVA).

We here report a patient with actinic prurigo. He had had erythematous papulovesicular eruptions on the sun-exposed sites from fall to early summer for 4 years. The lesions healed leaving atrophic scars. The histology showed epidermal necrosis and dermal dense perivascular lymphohistiocytic infiltration and edema. His minimal erythema doses to ultraviolet B (UVB) and UVA were normal and lowered, respectively. Skin lesions were produced by repeated irradiation with UVA plus UVB, but not with UVA alone. Then he was diagnosed as having actinic prurigo. Skin fibroblasts from the patient were hypersensitive to UVA. We believe that the hypersensitivity relates to the pathomechanisms of the photosensitivity in the case. UVA sensitivity of fibroblasts may be useful for differentiating actinic prurigo, hydroa vacciniforme, and other similar photosensitive disorders.