Photosensitivity reactions
Photosensitivity reactions: Excerpt from Professional Guide to Diseases (Eighth Edition)
A photosensitivity reaction is a skin eruption that can be a toxic or allergic response to light alone or to light and chemicals. A phototoxic reaction is a dose-related primary response. A photoallergic reaction is an uncommon, acquired immune response that isn’t dose-related — even slight exposure can cause a severe reaction.
Causes
Certain chemicals can cause a photosensitivity reaction, including dyes, coal tar, and furocoumarin compounds found in plants. The list of drugs that can cause photosensitivity reactions is extensive and includes many drugs within each of the following general categories: antibiotics (especially tetracycline), antidepressants, antihistamines, anticancer agents, antiparasitic agents, antipsychotic agents, diuretics, hypoglycemics, nonsteroidal anti-inflammatories, sunscreens, and miscellaneous agents, such as cardiac glycosides, hormonal contraceptives, and acne medications.
Berlock dermatitis, a specific photosensitivity reaction, results from the use of oil of bergamot — a common component of perfumes, colognes, and pomades.
Signs and symptoms
Immediately after exposure, a phototoxic reaction causes a burning sensation followed by erythema (sunburn-type reaction), edema, desquamation, and hyperpigmentation. Berlock dermatitis produces an acute reaction with erythematous vesicles that later become hyperpigmented.
Photoallergic reactions may take one of two forms. Developing 2 hours to 5 days after light exposure, polymorphous light eruption (PMLE) produces erythema, papules, vesicles, urticaria, and eczematous lesions on exposed areas; pruritus may persist for 1 to 2 weeks. Solar urticaria begins minutes after exposure and lasts about an hour; erythema and wheals follow itching and burning sensations.
Diagnosis
Characteristic skin eruptions in sun-exposed areas and a patient history of recent exposure to light or certain chemicals suggest a photosensitivity reaction. A photopatch test for ultraviolet A and B (UVA and UVB) done while the patient is on the drug may aid diagnosis and identify the causative light wavelength. Other studies must rule out connective tissue disease, such as lupus erythematosus and porphyrias.
Treatment
For many patients, treatment involves a sunscreen, protective clothing, and minimal exposure to sunlight while the patient continues on the drug. For others, progressive exposure to sunlight can thicken the skin and produce a tan that interferes with photoallergens and prevents further eruptions.
Withdrawal of the causative agent and treatment with oral steroids usually provides relief. The patient should be advised not to use the causative agent again if it’s known, even though this may limit the patient’s treatment options.
Antimalarial drugs, beta-carotene, and PUVA (psoralen and UVA) may be used to treat PMLE. Treatment for solar urticaria may also require PUVA. Although hyperpigmentation usually fades in several months, hydroquinone preparations can hasten the process.
Special considerations
❑ To prevent reactions, advise the patient to avoid prolonged exposure to light.
❑ Tell the patient to inform his physician about sensitivity to any drugs.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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