Photodermatology

Question 1

Define photosensitivity

Answer 1

Conditions triggered by light

Question 2

What is normal cutaneous photosensitivity?

Answer 2

Sun burn

Question 3

What are abnormal forms of photosensitivity?

Answer 3

Polymorphic light eruption, porphyria, lupus, drug eruptions

Question 4

How does photosensitivity occur?

Answer 4

UV absorbed by chromophore results in mediator release, inflammatory response and damage

Question 5

How can photosensitivity be treated?

Answer 5

Behavioural avoidance, hardening phototherapy/PUVA, chromophore removal, inhibition of mediator release

Question 6

What are porphyrias?

Answer 6

Enzyme problem in harm pathway leads to a build up of metabolites

Question 7

When do skin features of porphyrias occur?

Answer 7

When chemical affected absorbs light

Question 8

What are the three main porphyria?

Answer 8

• acute intermittent porphyria
• porphyria cutanea tarda
• erythropoietic protoporphyria

Question 9

Where can the build up of metabolites be detected?

Answer 9

Urine, faeces & blood

Question 10

What are the enzyme and metabolite involved in porphyria cutanea tarda?

Answer 10

Enzyme - uroporphyrinogen decarboxylase decrease in liver

Metabolite build up - uroporphyrinogen

Question 11

How does porphyria cutanea trade present?

Answer 11

Vesicles/bullae in sun exposed sites, hypertrichosifs & pigmentation, skin fragility & scarring

Question 12

Why do they symptoms arise?

Answer 12

Accumulation of porphyrins in the skin act as chromophores absorbing UV and subsequently causing damage

Question 13

State the causes of PCT

Answer 13

Liver disease, alcohol, haemochromatosis gene, HIV, HCV, oestrogen, vitamin C deficiency, idiopathic (sporadic)

Question 14

How is PCT investigated?

Answer 14

Woods Lamp

Question 15

What is the management of PCT?

Answer 15

Find & treat underlying cause

Question 16

What are the enzyme and metabolite involved in erythropoietic protoporphyria?

Answer 16

Enzyme - ferrochelatase

Metabolite - Protoporphyrin IX build up

Question 17

What causes erythropoietic protoporphyria?

Answer 17

Autosomal dominant condition presents in childhood

Question 18

How does erythropoietic protoporphyria present?

Answer 18

Mild anaemia, painful red blistering eruption, pitted linear scars on nose and hands

Question 19

What symptom often comes later in life?

Answer 19

Gallstones due to build up of protoporphyrin

Question 20

How is erythropoietic protoporphyria managed?

Answer 20

Genetic counselling, visible light photo protection, regular monitoring (6 monthly LFTs & RBC porphyrins)

Question 21

What is the only cure for erythropoietic protoporphyria?

Answer 21

Bone marrow transplant

Question 22

What are the enzyme and metabolite involved in acute intermittent porphyria?

Answer 22

Enzyme - PBG deaminase

Metabolite - Porphobilinogen (PBG)

Question 23

How will acute intermittent porphyria present?

Answer 23

Emergency - acute abdomen, psychosis, guillain barré, mononeuritis, malignant hypertension

Question 24

What causes acute intermittent porphyria?

Answer 24

Autosomal dominant inherited condition

Question 25

How is acute intermittent porphyria treated?

Answer 25

Symptomatic treatment, hematin can shorten attack & high dose carbohydrate can slow down the pathway to improve recovery