Photodermatology Flashcards
Define photosensitivity
Conditions triggered by light
What is normal cutaneous photosensitivity?
Sun burn
What are abnormal forms of photosensitivity?
Polymorphic light eruption, porphyria, lupus, drug eruptions
How does photosensitivity occur?
UV absorbed by chromophore results in mediator release, inflammatory response and damage
How can photosensitivity be treated?
Behavioural avoidance, hardening phototherapy/PUVA, chromophore removal, inhibition of mediator release
What are porphyrias?
Enzyme problem in harm pathway leads to a build up of metabolites
When do skin features of porphyrias occur?
When chemical affected absorbs light
What are the three main porphyria?
- acute intermittent porphyria
- porphyria cutanea tarda
- erythropoietic protoporphyria
Where can the build up of metabolites be detected?
Urine, faeces & blood
What are the enzyme and metabolite involved in porphyria cutanea tarda?
Enzyme - uroporphyrinogen decarboxylase decrease in liver
Metabolite build up - uroporphyrinogen
How does porphyria cutanea trade present?
Vesicles/bullae in sun exposed sites, hypertrichosifs & pigmentation, skin fragility & scarring
Why do they symptoms arise?
Accumulation of porphyrins in the skin act as chromophores absorbing UV and subsequently causing damage
State the causes of PCT
Liver disease, alcohol, haemochromatosis gene, HIV, HCV, oestrogen, vitamin C deficiency, idiopathic (sporadic)
How is PCT investigated?
Woods Lamp
What is the management of PCT?
Find & treat underlying cause
What are the enzyme and metabolite involved in erythropoietic protoporphyria?
Enzyme - ferrochelatase
Metabolite - Protoporphyrin IX build up
What causes erythropoietic protoporphyria?
Autosomal dominant condition presents in childhood
How does erythropoietic protoporphyria present?
Mild anaemia, painful red blistering eruption, pitted linear scars on nose and hands
What symptom often comes later in life?
Gallstones due to build up of protoporphyrin
How is erythropoietic protoporphyria managed?
Genetic counselling, visible light photo protection, regular monitoring (6 monthly LFTs & RBC porphyrins)
What is the only cure for erythropoietic protoporphyria?
Bone marrow transplant
What are the enzyme and metabolite involved in acute intermittent porphyria?
Enzyme - PBG deaminase
Metabolite - Porphobilinogen (PBG)
How will acute intermittent porphyria present?
Emergency - acute abdomen, psychosis, guillain barré, mononeuritis, malignant hypertension
What causes acute intermittent porphyria?
Autosomal dominant inherited condition
How is acute intermittent porphyria treated?
Symptomatic treatment, hematin can shorten attack & high dose carbohydrate can slow down the pathway to improve recovery