Photodermatology

Question 1

Difference between phototoxicity & photoallergy

Answer 1

Phototoxicity is when a drug causes increased sensitivity to sunlight
Photoallergy is when a drug caused a delayed type 4 reaction

Question 2

Define porphyria

Answer 2

Diseases in which porphyrins accumulate, leading to skin changes or neurological symptoms or both

Question 3

What does the body use porphyrins for?

Answer 3

Produce haem

Question 4

Only thing that helps blistering in acute phototoxic porphyria

Answer 4

Placing a wet towel on it

Question 5

Defective enzyme in porphyria cutanea tarda

Answer 5

Uroporphyrinogen decarboxylase

Question 6

Most affected area in PCT

Answer 6

Parts of the hands exposed to light

Question 7

How does PCT present?

Answer 7

Presents as small blisters & erosions on backs of hands, & on forearms & face
Milia (caused by bits of keratin, means disrupted DEJ)
Hyperpigmentation
Hypertrichosis
Solar urticaria
Morphoea (painless, discoloured patches on skin)

Question 8

Investigation for PCT

Answer 8

Water soluble porphyrins in urine, shine Woods lamp, should turn fluorescent

Question 9

Causes of PCT

Answer 9

Alcohol
Viral hepatitis
Oestrogens
Haemochromatosis

Question 10

Management of PCT

Answer 10

Relieve the skin disease

Treat the underlying diseases, to reduce the risk of liver cirrhosis, hepatoma, etc.

Question 11

What builds up in erythropoietic protoporphyria? Where does it build up?

Answer 11

Protoporphyrin IX

In erythrocytes

Question 12

Deficient enzyme in erythropoietic protoporphyria

Answer 12

Ferrochelatase

Question 13

Clinical presentation of erythropoietic porphyria

Answer 13

Painful photosensitivity which develops in childhood
A burning sensation occurs within minutes of exposure to sunlight
Soon the skin becomes swollen and crusted vesicles may appear, leading to pitted scars
Liver disease and gallstones occur
Burning sensation that is only relieved by cold

Question 14

Management of EPP

Answer 14

6 monthly LFTs & RBC porphyrins
Photoprotection from visible light
Prophylactic TL-01 phototherapy
Anti-oxidants (beta-carotene, cysteine, high dose vitamin C)
(Avoid iron)

Incipient liver failure: oral charcoal; cholestyramine; ? ALA synthase inhibition
Liver failure: transplant liver; ? Bone marrow