Solar urticaria with a wide action spectrum from UVB to visible light complicated with UVA‐induced polymorphous light eruption

Abstract

To the Editor, Solar urticaria and polymorphous light eruption (PLE) are acquired idiopathic photosensitivity disorders, but each phenomenon is extremely different; one is an immediate reaction, and one is a delayed-type reaction. Phototesting is necessary not only for the diagnosis of these photosensitivity disorders but also for the determination of the action spectrum so that the patient can try to avoid the triggering wavelengths in ordinary life. Solar urticaria is unique in that the particular spectra that inhibit or enhance the reactions by action spectra are present in some cases. In contrast, with PLE, phototesting is difficult, because a single or even repeated exposure of ultraviolet light or visible light sometimes fails to provoke the reaction. Here, we report a case of solar urticaria complicated with PLE. Solar urticaria with an action spectrum ranging from UVB to visible light was diagnosed by clinical presentation, phototesting and intradermal injections of photo-irradiated autologous serum. PLE induced by UVA was diagnosed by clinical presentation and phototesting. A 60-year-old man experienced erythematous skin eruptions on sun-exposed areas immediately after exposure to sunlight while riding a bicycle. The eruptions disappeared within 1 hour. The next day, he went fishing in the sun and experienced pruritic erythema and swelling on the face and dorsal surface of the hands. The swelling improved within a few hours, but erythema persisted until the following day. He is otherwise healthy and takes no medications. There were no abnormal laboratory findings, including antinuclear antibody and porphyria profiles. Photoprovocation tests were performed with a sunlamp (Philips Ultra Violet-B TL 20W12, Eindhoven, The Netherland) for UVB, a black light (Torex FL 20S, BL-BMR, Tokyo, Japan) for UVA and a slide projector (160W; Cabin Kogyo Co, Tokyo, Japan) for visible light. A single exposure to 3.0 J/cm of UVA (Fig. 1a), 8.7 mJ/cm of UVB (Fig. 1b) or visible light (Fig. 1c) at the target distance of 15 cm for 15 min induced erythema or wheal immediately after exposure. Erythema was observed in a visible light-irradiated area with a Y-50 cut-off filter (Fig. 1d), but not with a Y51 filter (Fig. 1e), indicating that the action spectrum in the visible light wavelengths was shorter than 500 nm. Skin reactions provoked by UVB and visible light faded within 45 min, but those provoked by UVA persisted for 30 h (Fig. 2a–c). Histological examination of the skin reaction 30 h after UVA irradiation revealed spongiosis and dense perivascular mononuclear cell infiltrations (Fig. 2d), compatible to polymorphous light eruption. Inhibitory and augmentation spectra were not observed. Next, the serum of the patient was examined for the presence of chromophore to induce urticaria. An aliquot of serum was exposed in vitro to 1.5 J/cm of UVA, 104 mJ/cm of UVB or 5 min of visible light alone or with an R60 cut-off filter; 0.1 ml of the exposed and