Photodermatology and the Porphyrias Flashcards
What is photosensitivity?
Cutaneous response to UVR and, in some individuals, to visible light
This can be normal (Fitzpatrick sun-reactive skin phototypes) or abnormal (reaction of skin to UVR is either quantitatively/qualitatively outwith that of the normal population)
Fitzpatrick sun-reactive skin phototypes?
Type I - always burns, never tans (pale white; blond or red hair; blue eyes; freckles)
Type II - usually burns, tans minimally (white; fair; blond or red hair; blue, green, or hazel eyes)
Type III - sometimes mild burn, tans uniformly (cream white; fair with any hair or eye color)
Type IV - burns minimally, always tans well (moderate brown)
Type V - very rarely burns, tans very easily (dark brown)
Type VI - never burns, never tans (deeply pigmented dark brown to darkest brown)
Two types of photosensitivities?
Photoallergy - drugs, topical or systemic, and chemicals on the skin can interact with UVR and cause immunological reactions
Phototoxicity - chemically induced skin irritation, requiring light, that does not involve the immune system.. Resembles an exaggerated sunburn
What is photocontact dermatitis?
Eczematous condition which is triggered by an interaction between an otherwise unharmful/less harmful substance on the skin and UV light; this can be either due to allergy or toxicity
What are photoaggravated dermatoses?
Exacerbations of any conditions that the patient already has, e.g: eczema,
Treatment options?
Behavioural avoidance, clothing, sunscreen use
Inhibition of mediator/action release and inhibition of inflammatory response
What are the porphyrias?
Rare inborn errors of metabolism, caused by enzyme abnormalities involved in the synthesis of haem; this results in the overproduction PORPHYRINS (intermediate compounds)
Main groups of porphyrias?
Phototoxic skin porphyria, e.g: erythropoetic protophyria
Blistering and fragility skin porphyria, e.g: porphyria cutanea tarda (PCT)
Acute attack porphyrias
Severe congenital porphyrias, ushc as congenital erythropoetic porphyria)
What is porphyria cutanea tarda (PCT) Type 1?
Present with bullous eruption on exposure to sunlight and is the most common porphyria; this heals with scarring
The condition has a genetic predisposition but aetiological agents may provoke the eruption, e.g: alcohol, Hep C virus, haemochromatosis, HIV
Presentation of PCT?
Typically, with BLISTERS and FRAGILITY but also with:
Hyperpigmentation
Hypertrichosis (abnormal hair growth, mainly on cheeks)
Solar urticaria
Morphoea (painless, discolored patches the skin)
Ix for PCT?
Urinary porphyrin levels are ABNORMALLY HIGH in PCT; this is evident in visible light and yields a pink fluorescence under Wood lamp radiation
What is erythropoetic protoporphyria?
Autosomal dominant trait that present with IRRITATION and BURNING PAIN in the skin on exposure to sunlight; protoporphyrin deposition can occur but liver is usually normal
Ix for EPP?
Fluorescence of the peripheral rbcs and by increased protoporhyrin in the rbcs and stool
Management of EPP?
6 monthly LFTs and RBC porphyrins must be tested
Visible light photoprotection measures from the sun and fluorescent lights (part. if surgery is needed)
Prophylactic TL-01 phototherapy
Anti-oxidants (beta-carotene) may reduce sun sensitivity
Avoid iron
Behavioural changes in EPP?
Clothing
Sunscreen (of little use)
