Photodermatology and the porphyrias

Question 1

How is the response of different skin types to light classified?

Answer 1

Fitzpatrick classification (I-IV)

Question 2

What are the porphyrias?

Answer 2

Heterogenous group of rare diseases caused by various errors of haem biosynthesis

Question 3

What are the consequences of:

a) accumulation of porphyrin precursors
b) accumulation of porphyrin

Answer 3

a) neurotoxicity

b) cutaneous photosensitivity alone

Question 4

What is the main cutaneous manifestation of porphyria?

Answer 4

Photosensitivity

Question 5

Other than the porphyrias, what kinds of conditions can lead to abnormal photosensitivity?

Answer 5

Idiopathic e.g. polymorphic light eruption
Xeroderma pigmentosum
Drug reaction
Photocontact dermatitis

Question 6

What is the most common subtype of porphyria? How does it present?

Answer 6

Porphyria subcutanea tarda

Blistering skin lesions (photosensitive) in middle age, hypertrichosis

Question 7

What are the features of an attack of acute intermittent porphyria?

Answer 7

GI- abdominal pain, vomiting
neuro- psychosis, peripheral neuropathy
CV- hypertension, tachycardia

Question 8

Describe the inheritance pattern of acute intermittent porphyria

Answer 8

Low penetrance AD

Around 28% de novo

Question 9

How does erythropoetic porphyria often present? What is the enzyme deficiency?

Answer 9

early childhood tingling, itch discomfort in the sun

ferrochetolase

Question 10

What is the enzyme deficiency in PCT?

Answer 10

Uroporphyrinogen decarboxylase

Question 11

What is the enzyme deficiency in acute intermittent porphyria?

Answer 11

Porphobilinogen deaminase