Defining Photosensitivity in Atopic Dermatitis

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Many diseases can be photoaggravated dermatoses, or exacerbated on exposure to optical radiation, including atopic dermatitis (AD). Although many studies have shown that AD can be improved by sunlight exposure, a subset of patients with AD have found their condition to be exacerbated by sunlight.¹

Research into photosensitivity in AD has explored the condition, but has not yet defined it as a single, unified entity. Different studies have described various forms of light-related aggravation, including terms like photoaggravated AD, photosensitive AD, photoexacerbated AD, photosensitive eczema, and chronic actinic dermatitis (CAD).^2-5 There has been inconsistency in the terminology and diagnostic criteria used to identify light sensitivity in AD depending on the phototesting center. With this in mind, the goal of a recent study was twofold: first, to review the photodiagnostic data of patients with AD who were referred to the Scottish Photobiology Service (SPS); and second, to use this data to establish consistent diagnostic criteria for identifying photosensitivity in AD.⁶

Methods

The SPS reviewed patients with AD suspected of light sensitivity between January 2017 and January 2023. The review focused on patients with rashes primarily on sun-exposed areas, worsening of symptoms after sunlight or phototherapy, or changes in the pattern or seasonality of AD. Key data collected included patient demographics, clinical features, photodiagnostic results, and outcomes, with lupus and drug-induced photosensitivity ruled out.

Photobiological assessments included monochromator phototesting at various UV wavelengths to determine the minimal erythema dose (MED), and narrowband UVB testing. Abnormal MEDs were identified based on comparisons with healthy volunteers. Photoprovocation and photopatch testing were conducted as needed, with readings interpreted according to established guidelines. Final diagnoses were categorized into three groups: Photo-Exacerbated AD (PEAD), Photo-Sensitive AD (PSAD), and Chronic Actinic Dermatitis (CAD).

Results

Over the study period, 139 patients with AD were assessed for photosensitivity. The cohort had a higher proportion of males (61.9%) with an average age of 42.6 years. Most patients had skin phototype I-III, and many also had comorbid allergic rhinitis and asthma. The diagnoses were categorized into 71 patients (51.1%) fell into the PEAD category, 57 patients (41%) into CAD, and 11 patients (7.9%) into CAD.

Researchers found that patients with CAD typically experienced rash from light exposure in less than an hour, with symptoms appearing within a day. In contrast, patients with PEAD and PSAD generally needed longer exposure to develop symptoms. Patients with CAD were more likely to have rash triggered through clothing and were less likely to have perennial rashes compared to those with PEAD and PSAD.

They found that monochromator phototesting results were normal for patients with PEAD, but patients with CAD exhibited marked UVB sensitivity. In patients with CAD, 93% showed sensitivity to UVB, while patients with PSAD displayed slight UVA sensitivity. The study statedTL-01 MED testing showed normal results for patients with PEAD, but 37.5% of patients with CAD had abnormally low TL-01 MEDs. Broadband UVA photoprovocation testing revealed to researchers positive reactions in a few patients, and photopatch testing showed high positivity rates across all groups.

Researchers reported vitamin D levels were frequently insufficient among the patients, but there were no significant differences in vitamin D status, IgE levels, or quality of life scores between the diagnostic groups. Notably, they found some patients’ photosensitivity status changed over time; for example, 2 patients with PSAD evolved into CAD, while 4 patients with CAD reverted to PEAD, and 2 showed resolution of UVB sensitivity.

Additionally, 5 patients in the PEAD group were found to have co-existing polymorphic light eruption (PLE), a condition distinct from their AD symptoms. Monochromator phototesting for these patients was normal, but photoprovocation testing demonstrated typical papular PLE changes in some cases.

Conclusion

The study proposed diagnostic criteria for 3 categories of photosensitivity in AD: PEAD< PSAD, and CAD. These categories represent a spectrum of the disease, with potential for patients to shift between categories over time. Researchers stated the findings underscore the importance of photodiagnostic tests, as clinical assessment alone may be insufficient. They noted repeated phototesting can be crucial for detecting changes in diagnostic classification, especially if clinical features evolve. Awareness of these potential changes is important for both patients and clinicians to best understand and treat the disease.

References

1. O'Gorman SM, Murphy GM. Photoaggravated disorders. Dermatol Clin. 2014;32(3):385-ix. doi:10.1016/j.det.2014.03.008
2. ten Berge O, van Weelden H, Bruijnzeel-Koomen CA, de Bruin-Weller MS, Sigurdsson V. Throwing a light on photosensitivity in atopic dermatitis: a retrospective study. Am J Clin Dermatol. 2009;10(2):119-123. doi:10.2165/00128071-200910020-00004
3. Ellenbogen E, Wesselmann U, Hofmann SC, et al. Photosensitive atopic dermatitis--a neglected subset: Clinical, laboratory, histological and photobiological workup. J EurAcad Dermatol Venereol. 2016;30(2):270-275. doi:10.1111/jdv.13451
4. Rutter KJ, Farrar MD, Marjanovic EJ, et al. Clinicophotobiological characterization of photoaggravated atopic dermatitis. JAMA Dermatol. 2022;158(9):1022-1030. doi:10.1001/jamadermatol.2022.2823
5. Gao H, Zhang Z, Ma L, et al. Photosensitivity is an important cause of refractory facial erythema in atopic dermatitis: A retrospective study of 82 Chinese patients. Photodermatol Photoimmunol Photomed. 2023;39(4):318-324. doi:10.1111/phpp.12836
6. C, Dawe R, Lesar A, et al. Continuum of light sensitivity in atopic dermatitis: A retrospective analysis of 139 cases in Scotland. J Am Acad Dermatol. 2024. doi:10.1016/j.jaad.2024.07.1502