Diagnostic Considerations
Polymorphous light eruption (PLE) is the main condition that can be misdiagnosed as actinic prurigo. PLE is the most frequent photodermatosis worldwide; however, its lesions are limited to skin and appear during spring and resolve after spring. Actinic prurigo (AP) lesions persist during autumn and winter and have some other features. They are bilateral and symmetric, affecting sun-exposured areas of the skin, and are located in the supraciliary, malar, nasal, and labial areas of the face. Other parts of the body are affected, such as the neck, upper thorax, limbs, and hands (especially external and dorsal aspects). The primary lesions consist of erythematous papules that converge into very pruriginous plaques. Secondary observed lesions are excoriations, serohematic crusts, hyperinflammatory or hypoinflammatory pigmentation, and atrophic scars. Contrary to PLE, at least half the patients exhibit cheilitis. It usually manifests on the lower lip as erythema, edema, and erosions. In one fourth of those affected, cheilitis is the only manifestation. [3, 13, 22, 23] In addition to cheilitis, almost half the patients also show conjunctivitis with symptoms such as pruritus, hyperemia, photophobia, and pseudopterygium. [4, 34]
As most of patients first develop symptoms during childhood, the main clinical consideration in this population is to rule out atopic dermatitis with photosensitivity, particularly in those who are not aware of preexistent atopy. In these patients, it is generally recognized because their nose skin usually is not affected. However, actinic prurigo conjunctivitis should also be distinguished from atopic or allergic spring conjunctivitis. [4] In actinic prurigo patients, usually the conjunctival pruritic symptoms are not as intense as those associated with atopy. The presence of cheilitis and conjunctivitis is an infrequent finding in atopic patients. However, it must be distinguished from dry skin and cracking from atopic labial and perioral dermatitis.
In adults, photoallergic contact dermatitis and chronic actinic dermatitis are other conditions the clinician must rule out when patients have photosensitivity of a chronic nature. A photoallergic contact dermatitis diagnosis is supported by positive photo patch testing with the application of a photoallergen series activated by 5 J/cm2 UVA and checking the results 2-4 days later. [35] Chronic actinic dermatitis usually is more common in men than women; it starts after age 50 years in patients who live away from the equator. Apart from sunlight sensitivity, those affected have associated allergies to other substances. [36]
Differential Diagnoses
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Itchy plaques mainly on photoexposed areas of the face; these plaques are characteristic of actinic prurigo.
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Photodistribution of lesions over the body. Note the hypopigmented areas of the skin, which are very common after intense scratching in children.
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Multiple itchy papules coalescing into plaques on the neck. These lesions are similar to lesions of polymorphous light eruption. Note the excoriations induced by scratching.
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One third of patients are children. The nose is frequently affected. This clinical feature is useful in distinguishing it from other entities, such as atopic dermatitis.
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One half of patients have bilateral conjunctivitis. Eye protection is needed to avoid disease progression.
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About 75% of patients have cheilitis, which can take the form of solid lesions or erosions.
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A phototest with UV-B light shows reproduction of lesions on the inner aspect of the arm. The result from the phototest with UV-A light was negative.
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Histologic examination shows acanthosis, mild spongiosis, edema of the lamina propria, and a moderate-to-dense perivascular lymphocytic inflammatory infiltrate.
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A close-up view shows edema of the lamina propria as well as a lymphocytic inflammatory infiltrate in the dermis.
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Young girl with a history of atopic dermatitis and itchy, lichenified plaques on her face for the last 3 months. Atopic dermatitis with photosensitivity is the main differential diagnosis with actinic prurigo in children.
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Actinic cheilitis resulting from actinic prurigo.
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Erythematous and very itchy plaques on solar exposure areas of the face and pseudopterygium are commonly observed in actinic prurigo.
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Lichenified plaques, excoriated nodules, and atrophic scars on the dorsal aspect of hands are frequently seen in children.
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Contact dermatitis due to sunscreen in a patient with actinic prurigo.
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Impetiginous area located on the right ear lobe due to intense scratching following an acute relapse.
