Photodermatology Flashcards
(25 cards)
What is cutaneous photosensitivity?
An abnormal skin response to exposure to UV or visible light
Examples of cutaneous photosensitivity include phototoxicity and photoallergy.
Define these.
Phototoxicity = a condition involving skin irritation to sunlight or other forms of light
Photoallergy = a form of allergic contact dermatitis where the allergen must be activated by light to illicit a response
Describe the Fitzpatrick scale of sun-reactive skin phototypes (type I - VI)
Type I: always burns, never tans
Type II: usually burns, may then tan
Type III: sometimes burns but tans after a few exposures
Type IV: rarely burns, tans very easily
Type V: naturally brown skin
Type VI: naturally black skin
Which site is often affected in cutaneous photosensitivity?
Behind the ear (retro-auricular)
What are porphyrias?
A group of disorders caused by a buildup of porphyrin in the body - usually in the skin or nervous system
Porphyrias are usually caused by…
Hepatic disorders
What porphyrins are involved in skin porphyrias?
Porphyrins as chromophores (chemicals that absorb radiation)
What are the 4 main types of skin porphyrias?
1) Phototoxic (e.g., erythropoietic protoporphyria)
2) Blistering and fragility
3) Acute attack
4) Severe congenital
List 4 common features of skin porphyria
- Fragility
- Blisters
- Erosions
- No visible change but tingling pain lasting days after an exposure
Skin porphyrias are common/rare in Scotland
Rare
What is the most common skin porphyria and what is it caused by?
Porphyria cutanea tarda (PCT)
Caused by a defect in the liver enzyme uroporphyrinogen decarboxylase (UROD)
What are the clinical features of porphyria cutanea tarda (PCT)?
On sun-exposed sites…
- Blisters (+/-blood)
- Erosions
- Milia (lots of tiny white cysts)
- Scleroderma-like changes
- Hyperpigmentation
- Solar urticaria (swelling within minutes of sun exposure)
What causes the clinical features seen in porphyrias?
Photosensitivity due to excess porphyrin in the skin
What investigations are done for porphyria cutanea tarda (PCT)?
- Woods Lamp (turns urine sample coral pink under fluorescence due to excess porphyrins)
- Test porphyrin levels in blood, urine and faeces (elevated)
- Liver function tests
What test is diagnostic for porphyria cutanea tarda (PCT)?
Elevated isocoproporphyrin in the faeces
How is porphyria cutanea tarda (PCT) managed?
- Minimise skin exposure (e.g., covering clothing when outdoors, suncream)
- Treat underlying liver disease
What are underlying causes that may result in defect in the liver enzyme uroporphyrinogen decarboxylase (UROD) and lead to porphyria cutanea tarda (PCT)?
- Hereditary
- Alcohol
- Viral hepatitis (C)
- Oestrogen/ hormone treatment
- Haemochromatosis
What is erythropoietic protoporphyria (EPP)?
The second most common porphyria, caused by an autosomal codominant inherited deficiency of the enzyme ferrochelatase
Why is photosensitivity seen in erythropoietic protoporphyria (EPP)?
Reduced activity of the enzyme ferrochelatase results in a build-up of protoporphyrin
What are the clinical features of erythropoietic protoporphyria (EPP)?
- Skin pain on exposure to sunlight, lasting for days after exposure
- Crying in the sun in children
- Often no visible changes
- Thickening and pitting of sun-exposed skin over years
- Pain may be provoked immediately or hours after exposure
What investigations are done for erythropoietic protoporphyria (EPP)?
- RBC porphyrins (elevated)
- Genetic testing for mutations in the ferrochelatase gene
What liver disease is common in patients with erythropoietic protoporphyria (EPP)?
Gallstones
How is erythropoietic protoporphyria (EPP) managed?
- Genetic counselling (inherited disease with no cure)
- 6 monthly LFTs and RBC porphyrins
- Visible light photoprotection (e.g., avoid peak sunlight times, cover up outdoors)
Why is suncream not useful in erythropoietic protoporphyria (EPP)?
It doesn’t block visible light
