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LR Dermatology > Photodermatology > Flashcards

Photodermatology Flashcards

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Dermatology Board Prep flashcards
1
Q

What is cutaneous photosensitivity?

A

An abnormal skin response to exposure to UV or visible light

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2
Q

Examples of cutaneous photosensitivity include phototoxicity and photoallergy.

Define these.

A

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

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3
Q

Describe the Fitzpatrick scale of sun-reactive skin phototypes (type I - VI)

A

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

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4
Q

Which site is often affected in cutaneous photosensitivity?

A

Behind the ear (retro-auricular)

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5
Q

What are porphyrias?

A

A group of disorders caused by a buildup of porphyrin in the body - usually in the skin or nervous system

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6
Q

Porphyrias are usually caused by…

A

Hepatic disorders

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7
Q

What porphyrins are involved in skin porphyrias?

A

Porphyrins as chromophores (chemicals that absorb radiation)

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8
Q

What are the 4 main types of skin porphyrias?

A

1) Phototoxic (e.g., erythropoietic protoporphyria)
2) Blistering and fragility
3) Acute attack
4) Severe congenital

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9
Q

List 4 common features of skin porphyria

A
  • Fragility
  • Blisters
  • Erosions
  • No visible change but tingling pain lasting days after an exposure
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10
Q

Skin porphyrias are common/rare in Scotland

A

Rare

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11
Q

What is the most common skin porphyria and what is it caused by?

A

Porphyria cutanea tarda (PCT)

Caused by a defect in the liver enzyme uroporphyrinogen decarboxylase (UROD)

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12
Q

What are the clinical features of porphyria cutanea tarda (PCT)?

A

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)
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13
Q

What causes the clinical features seen in porphyrias?

A

Photosensitivity due to excess porphyrin in the skin

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14
Q

What investigations are done for porphyria cutanea tarda (PCT)?

A
  • 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
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15
Q

What test is diagnostic for porphyria cutanea tarda (PCT)?

A

Elevated isocoproporphyrin in the faeces

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16
Q

How is porphyria cutanea tarda (PCT) managed?

A
  • Minimise skin exposure (e.g., covering clothing when outdoors, suncream)
  • Treat underlying liver disease
17
Q

What are underlying causes that may result in defect in the liver enzyme uroporphyrinogen decarboxylase (UROD) and lead to porphyria cutanea tarda (PCT)?

A
  • Hereditary
  • Alcohol
  • Viral hepatitis (C)
  • Oestrogen/ hormone treatment
  • Haemochromatosis
18
Q

What is erythropoietic protoporphyria (EPP)?

A

The second most common porphyria, caused by an autosomal codominant inherited deficiency of the enzyme ferrochelatase

19
Q

Why is photosensitivity seen in erythropoietic protoporphyria (EPP)?

A

Reduced activity of the enzyme ferrochelatase results in a build-up of protoporphyrin

20
Q

What are the clinical features of erythropoietic protoporphyria (EPP)?

A
  • 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
21
Q

What investigations are done for erythropoietic protoporphyria (EPP)?

A
  • RBC porphyrins (elevated)

- Genetic testing for mutations in the ferrochelatase gene

22
Q

What liver disease is common in patients with erythropoietic protoporphyria (EPP)?

A

Gallstones

23
Q

How is erythropoietic protoporphyria (EPP) managed?

A
  • 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)
24
Q

Why is suncream not useful in erythropoietic protoporphyria (EPP)?

A

It doesn’t block visible light

25
Q

Is dark or light clothing preferable for photoprotection?

A

Dark because light can pass through white clothing more easily

LR Dermatology (11 decks)

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