| disease | Polymorphous Light Eruption |
| alias | Polymorphous Light Eruption |
Polymorphous Light Eruption is a chronic photosensitive skin disorder characterized by recurrent and diverse eruptions.
bubble_chart Etiology
The exact cause of the disease is not yet fully understood, but genetic and geographical factors may be important contributing elements. Most believe it is a delayed allergic reaction triggered by sunlight sensitivity. The condition involves immune sensitization to skin antigens altered by ultraviolet radiation. The primary pathogenic spectrum is medium-wave ultraviolet light. The duration and intensity of sun exposure vary significantly among patients. Some individuals have a family history of photosensitivity.
bubble_chart Pathological Changes
Dermal papilla edema, pale and lavender, with dense lymphocytic infiltration around the superficial and deep dermal blood vessels. Some cases show epidermal changes such as spongiotic edema, intraepidermal vesicles, and individual necrotic keratinocytes. In others, only perivascular inflammation is observed in the superficial or deep dermis without significant papillary edema.
bubble_chart Clinical Manifestations
The disease is more common in adults, often occurring in late spring and early summer, and naturally resolving in autumn and winter. Skin lesions predominantly appear on sun-exposed areas, with the face and neck being the most frequently affected. The rash is polymorphous, with a course lasting about 3 to 5 months. Based on the morphology of the rash, it can be classified into four types.
1. Patch type: The rash presents as red or dark red patches or slightly raised infiltrative patches, approximately 20–25 mm in size. In severe or prolonged cases, peripheral capillary dilation and poikiloderma may occur. Post-inflammatory hyperpigmentation remains after the rash subsides. Intense pruritus is present. This type is the most common.
2. Erythema multiforme type: The rash consists of red or dark red edematous papules of varying sizes with well-defined borders and slightly raised edges.3. Eczema type: The skin appears erythematous and swollen, with dense pinhead- to rice-sized papules, vesicles, erosions, crusts, and scaling, resembling an eczematous appearance. Sometimes lichenification occurs, accompanied by intense pruritus. This type is rare.
4. Prurigo type: The rash manifests as erythema, rice- to mung bean-sized papules, and nodules. Prolonged cases may develop lichenification. Post-inflammatory hyperpigmentation remains after resolution. Subjective cutaneous pruritus is present. This type is rare.
bubble_chart Treatment Measures
1. Local Treatment Before going out, apply 15% zinc oxide ointment, 5% titanium dioxide cream, 4% benzophenone lotion or cream, dihydroxyacetone and naphthoquinone lotion, or corticosteroid cream, 2-3 times daily.
2. Systemic Treatment
(1) Antihistamines: Cyproheptadine 2-4 mg; Chlorphenamine 4-8 mg, taken orally once daily. Astemizole 10 mg; Loratadine 10 mg, taken orally once daily.
(2) Antimalarials: Chloroquine 250 mg, taken orally 2-3 times daily. After symptom control, reduce the dose to once daily for 1-2 weeks, then gradually decrease the dosage every 2-4 days. Hydroxychloroquine sulfate 100 mg, taken orally once daily. Monitor for side effects during treatment, with the latter having milder side effects than the former.
(3) Corticosteroids: Used for severe rashes, especially eczematous eruptions. Prednisone 30-40 mg daily, taken orally. After one week, gradually reduce the dose until discontinuation once symptoms are controlled.
(4) Azathioprine: Effective for patients with severe photosensitivity and eczematous changes. Some reports indicate successful treatment of severe polymorphous light eruption with azathioprine, but the author suggests it is unsuitable for most patients. It is only recommended as a short-term intermittent therapy for non-reproductive-age patients with severe polymorphous light eruption unresponsive to other treatments. Dose: 50 mg, twice daily, typically leading to remission in 2-4 months. A few patients may discontinue after 6-8 months. Regular monitoring of white blood cells, platelets, and liver function is required during treatment.
3. Photochemotherapy: 8-Methoxypsoralen combined with long-wave ultraviolet (PUVA) irradiation is effective for active lesions. Take 20 mg of 8-methoxypsoralen orally two hours before PUVA exposure, starting with the minimal phototoxic dose or 1 joule. Pre-treatment before late spring or early summer may also have a preventive effect.
4. Traditional Chinese Medicine Treatment: - For wind-dampness type, the principle is to dispel wind and clear heat. The formula can be modified Jing Fang Tang (Schizonepeta and Ledebouriella Decoction). - For blood-heat type, the principle is to cool blood and clear heat, using Xiao Feng Tang (Wind-Eliminating Decoction). - For eczematous changes, modified Gentian Liver-Draining Decoction can be used. - For prurigo-like changes, combine Peony and Gardenia Peripatetic Powder with Peach Kernel, Carthamus and Four-Ingredient Decoction for modification.
The principle is to avoid light, but it's also important to regularly engage in outdoor activities to receive small doses of short-term UV exposure, gradually increasing the amount of light to enhance the body's tolerance to light exposure. Avoid direct sunlight between 10 AM and 3 PM. Those who must work outdoors should wear protective clothing, straw hats, gloves, etc.
Based on the medical history, seasonal predisposition, chronic course, and abnormal reactions in the ultraviolet erythema test, the diagnosis is not difficult. This disease needs to be differentiated from the following conditions:
1. Eczema — The skin lesions are unrelated to exposure or season.
2. Erythema multiforme — Lesions are mostly seen on the hands and feet. If typical iris-like erythema is present, differentiation is easier. The onset is unrelated to light exposure.
3. Lupus erythematosus — The rash presents as persistent erythema with keratotic scales, dilated hair follicles, atrophic scars, and telangiectasia.
4. Neurodermatitis — The papules are flat and follow the skin lines, unrelated to light exposure and unaffected by seasons.
