Photodermatology and the porphyrias Flashcards
How is the response of different skin types to light classified?
Fitzpatrick classification (I-IV)
What are the porphyrias?
Heterogenous group of rare diseases caused by various errors of haem biosynthesis
What are the consequences of:
a) accumulation of porphyrin precursors
b) accumulation of porphyrin
a) neurotoxicity
b) cutaneous photosensitivity alone
What is the main cutaneous manifestation of porphyria?
Photosensitivity
Other than the porphyrias, what kinds of conditions can lead to abnormal photosensitivity?
Idiopathic e.g. polymorphic light eruption
Xeroderma pigmentosum
Drug reaction
Photocontact dermatitis
What is the most common subtype of porphyria? How does it present?
Porphyria subcutanea tarda
Blistering skin lesions (photosensitive) in middle age, hypertrichosis
What are the features of an attack of acute intermittent porphyria?
GI- abdominal pain, vomiting
neuro- psychosis, peripheral neuropathy
CV- hypertension, tachycardia
Describe the inheritance pattern of acute intermittent porphyria
Low penetrance AD
Around 28% de novo
How does erythropoetic porphyria often present? What is the enzyme deficiency?
early childhood tingling, itch discomfort in the sun
ferrochetolase
What is the enzyme deficiency in PCT?
Uroporphyrinogen decarboxylase
What is the enzyme deficiency in acute intermittent porphyria?
Porphobilinogen deaminase
