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Miscellaneous dermatology

Photosensitivity key points test

Which of the following reactions suggest photosensitivity? #! Sunburn in July in New Zealand # An itchy rash affecting the eyelids #! Dermatitis confined to the face and backs of hands #! Linear hyperpigmentation Explanation: Photosensitivity describes an abnormal response of the skin to light and may result in sunburn or a variety of rashes. Distribution involves areas exposed to the light, predominantly face, neck, backs of hands, lower legs and tops of feet. It rarely affects the eyelids. Linear hyperpigmentation is characteristic of phytophotodermatitis. Which of the following tests may be useful in suspected photosensitivity? #! Monochromator phototesting #! Antinuclear antibody #! 24-hour urinary porphyrins #! Patch testing Explanation: Tests in patients with suspected photosensitivity may include patch and photopatch testing, skin biopsy, monochromator and broadband phototesting, antinuclear antibodies and evaluation of blood, urine and faeces for porphyrins. Which of the following statements is true for sunburn? # It results in maximal erythema within four hours of exposure # It may spread to affect covered skin adjacent to exposed sites #! May be accompanied by headache, fever, lassitude #! In type 2-6 skin, is followed by tanning within 7 days Explanation: Sunburn is maximal about eight hours after exposure and is confined to exposed sites. Tanning occurs within 7 days. Severe sunburn may result in systemic symptoms. Which of the following statements is true for photosensitive dermatitis? # It is most often provoked by exposure to UVB radiation #! It may be caused by topical irritants and allergens #! It may be caused by oral toxins and allergens #! It may persist for months after the original cause has been removed Explanation: Photosensitive dermatitis is more often due to UVA than UVB and may be caused by local or systemic factors. Occasionally the skin remains photosensitive after the irritant or allergen has been removed. Which of the following statements is true for phytophotodermatitis? # Characteristically it results in a symmetrical eruption # It is often caused by oral methoxsalen #! It may arise through window glass #! It may cause persistent pigmentation Explanation: Phytophotodermatitis is UVA photosensitivity affecting skin in contact with plants containing psoralens and may rarely arise by exposure to sunlight through window glass. Asymmetrical linear blisters arise that cause persistent pigmented streaks. Which of the following statements is true for drug-induced photosensitivity? #! Phototoxic drugs include bendrofluazide and amiodarone #! Doxycycline may cause onycholysis #! Quinidine may cause a photosensitive lichenoid eruption #! May spread to affect covered skin adjacent to exposed sites Explanation: Phototoxic drugs include sulphonamides, thiazides, tetracyclines, phenothiazines, nalidixic acid, amiodarone, naproxen and psoralens. Onycholysis (separation of nail plate from nail bed) is occasionally due to drug photosensitivity. Quinine and quinidine may cause photosensitivity with lichenoid features. Although the rash is always most severe in sun exposed sites, it may rarely affected lightly covered areas or spread by autosensitisation. Which of the following skin diseases are aggravated by sun exposure? # Systemic sclerosis # Asteatotic dermatitis #! Porphyria cutanea tarda # Ascorbic acid deficiency Explanation: Photoaggravated dermatoses include cutaneous lupus erythematosus, dermatomyositis, atopic dermatitis, psoriasis, and some genodermatoses including hepatic porphyrias. Polymorphous light eruption (PMLE): # Idiopathic photosensitivity eruption affecting elderly men #! Often spares face and hands #! Most commonly causes irritable clustered papules on the forearms #! Clears within a few days of sun avoidance Explanation: PMLE is a common idiopathic photosensitivity eruption affecting young adult women that often spares habitually exposed areas (face and hands). It most commonly causes irritable clustered papules or papulovesicles on the forearms and clears within several days of sun avoidance. Chronic photosensitivity dermatitis / actinic reticuloid: *! Idiopathic photosensitivity eruption affecting elderly men * Often spares face and hands * Most commonly causes irritable clustered papules on the forearms * Clears within a few days of sun avoidance Explanation: Idiopathic chronic photosensitivity dermatitis mainly affects elderly men and may result in extreme photosensitivity on all exposed sites that persists throughout the year. Photoprotection * Narrow-spectrum sunscreens are adequate protection for patients with UVA sensitivity *! Photosensitivity eruptions may be provoked by artificial sources of light . *! Sunscreens are ineffective for porphyria even if applied 2-hourly . * Patients who are sensitive to UVB should cover the face with a welding mask * Photosensitive patients do not need to cover up when indoors *! Photosensitivity eruptions may be provoked by artificial sources of light * Sunscreens are ineffective even if applied 2-hourly * Patients who are sensitive to UVB should cover the face with a welding mask Explanation: Patients with photosensitivity should cover up and apply sunscreens to exposed skin 2-hourly while outdoors. Some severely affected individuals may also react to artificial sources of visible light. The protection provided by sunscreens against sunburn may be adequate for UVB sensitivity (e.g. type 1 skin) but even broad-spectrum products may not completely protect those with UVA sensitivity. They are unhelpful in porphyria because this is provoked by visible light.