Frequency of occurrence of polymorphic light eruption in patients treated with photohardening and patients treated with phototherapy for other diseases

Abstract Background Medical phototherapy can lead to the manifestation of polymorphic light eruption (PLE), though little is known about the frequency of such events. Aims The aim of this Austrian single center study was to retrospectively investigate over a 4‐year time period the frequency of PLE in patients prone to the condition and patients with other diseases under phototherapy (mainly narrow‐band and broad‐band UVB). Materials and Methods The data for analysis were obtained from the electronic health and patient record database and patient files of the Photodermatology Unit, Department of Dermatology, Medical University of Graz, Austria. Results PLE occurred in 24.3% (18/74) of PLE patients but only 0.7% (3/421) of psoriasis patients under phototherapy (chi‐square; P < 0.0001). PLE also occurred in 1.2% (3/257) of patients with atopic eczema, 0.8% (1/118) with prurigo, 3.5% (4/115, P = 0.0206) with parapsoriasis en plaques/mycosis fungoides, 7.4% (2/27, P = 0.0013) with granuloma anulare, 14.3% (1/7, P = 0.0002) with scleroderma, and 16.7% (1/6, P < 0.0001 vs. psoriasis) with pityriasis lichenoides chronica or pityriasis lichenoides eruptiva et varioliformis acuta. Discussion and Conclusion These results are helpful for treatment allocation and risk estimation of PLE occurrence with regard to obtaining informed consent not only from PLE‐prone patients but also from patients with other skin disorders commonly treated by phototherapy.


| INTRODUC TI ON
Polymorphic light eruption (PLE) is the most common photodermatosis and is especially prevalent among young women in temperate climates. 1 Severely affected individuals, who experience repeated attacks of PLE throughout the summer, may require prophylactic medical photohardening each spring before the first intense sun exposure. Medical photohardening simulates the naturally occurring phenomenon of hardening and aims to induce photoadaption. Broadband UVB (290-320 nm) (BB-UVB), narrowband UVB (311-313 nm) (NB-UVB), and psoralen plus UVA (PUVA) photochemotherapy are effective in photohardening of PLE. [2][3][4][5][6][7] Although it is well known that medical phototherapy can lead to PLE, little is known about the frequency of such events. The aim of this study was to investigate the frequency of PLE under prophylactic photohardening in PLE-prone patients. Additionally, we investigated the

| Statistical analysis
Descriptive data from our analyses were presented in tables. The Fisher exact or chi-square test, as appropriate, was used to compare the prevalence of PLE under phototherapy between different groups of patients. A P value P < 0.05 was considered significant.

| RE SULTS
Our electronic database search identified the occurrence of PLE under photohardening (in any cycle) in 24.3% (18/74) of PLE patients (Table 1). Photohardening with suberythemal dosages of NB-UVB had been administered to all PLE patients during phototherapy treatment cycles 2-3 times per week for 4-6 weeks in spring, at a starting dose of 0.2 J/cm 2 and in dose increments of 0.05-0.1 J/cm 2 per treatment, as tolerated. 8 The other forms of phototherapy had been administered to the PLE patients, as previously described. 7 The frequency of PLE in patients with other diseases treated with minimal photoxic dose-or skin phototype-based suberythemal phototherapy ranged from 0.4% (psoriasis) to 16.7% (PLEVA). PLE occurred significantly more often in PLE-prone patients who underwent photohardening than in psoriasis patients who underwent phototherapy (P < 0.0001). Compared with its occurrence in patients with psoriasis (the disease with the lowest observed prevalence of PLE), PLE occurred significantly more often under phototherapy in patients with parapsoriasis en plaques/mycosis fungoides (3.5%, P = 0.0206), granuloma anulare (7.4%, P = 0.0013), scleroderma (14.3%, P = 0.0002), and PLEVA (16.7%, P < 0.0001) ( Table 1). The frequency of PLE in patients with atopic eczema and prurigo was low and did not differ statistically from that in patients with psoriasis. PLE occurrence did not appear to be affected by wavebands or phototherapeutic modalities administered to the patients ( Table 1).
The demographics and phototherapy characteristics of PLE patients undergoing phototherapy are presented for individual patients in Table 2 and then summarized in Table 3. Under daily life conditions and exposure to natural sunlight, more women than men experienced PLE under photohardening (ie, 16 vs 2) (Table 1), consistent with the observation that more women than men overall had undergone photohardening. Surprisingly, however, the female/male ratio in non-PLE patients (7/9) was more balanced, despite a similar overall number of phototherapy-treated women and men in non-PLE patient groups. Besides, there were no major differences in phototherapy characteristics between PLE patients and non-PLE patients.
For instance, in PLE patients, the disease manifested after a median of five treatment exposures in the first cycle of occurrence, compared with 5.5 treatment exposures in non-PLE patients (Table 3). In general, the occurrence of PLE in a patient did not result in a change of the allocated standard treatment protocol, though some of them received short-term topical steroids to mitigate the rash.

| D ISCUSS I ON
In this Austrian study, PLE occurred in 24% (18/74) of PLE patients under photohardening, a percentage considerably lower than the 56% (44/79) recently reported in a 5-year single-center, case-series review from Scotland. 5 The reasons for this difference remain elusive, but may be partly due to differences in phototherapy treatment protocols and/or skin phototype. In our study, the minority (21%,  PLE in psoriasis might not be so rare in the general population. 9 PLE seems to be highly linked to photosensitive variants of psoriatic disease. In an epidemiologic study, 43% of all patients suffering from photosensitive psoriasis were found to have a history of PLE with secondary exacerbation of psoriatic lesions. 10 We recently specu- treatment, including one patient with scleroderma. PLE seems to be induced more often by UVA (320-400 nm) than by UVB (290-320 nm), but can also be induced by UVB alone and sometimes by both wavebands together (cited in 2 ). The role of UVA in triggering PLE has been well substantiated by phototest findings and the observation that most patients with PLE are sensitive to sunlight through window glass (cited in 2 ) and by the observed lack of protection from pure UVB-absorbing sunscreens. 13 Although the generalizability of our study's findings is limited by the rather low patient numbers in some of the diseases examined and by the retrospective study design, our findings do suggest that PLE manifestation under photohardening occurs frequently in PLE-prone patients but variably in other diseases treated with phototherapy. This knowledge will be helpful for allocating treatment, estimating risk of PLE occurrence, and obtaining related informed consent not only from PLE-prone patients but also from patients with other skin disorders commonly treated with phototherapy.