Intro to Phototoxicity and the Porphyrias Flashcards
what are the 2 different types of cutaneous photosensitivity
phototoxicity and photoallergy
what is the scale used to identify normal cutaneous photosensitivity
Fitzpatrick sun-reactive skin phototypes
I to IV, sometimes V and VI used
a 32 year old exposed to 1 hour midday sun gets sunburn and then tans afterwards, what type of skin phototype is he
II
which skin site is a clue to cutaneous photosensitivity
retroauricular(behind the ear)
what is involved in all the skin porphyrias
all involve porphyrines as chromophores, the chemicals that absorb radiation
where do manifestations of porphyrias arise
where the porphyrines accumulate, whcih depends on how water or fat soluble they are
what are the 4 main groups of porphyrias
phototoxic skin porphyrias
blistering + fragility skin porphyrias
acute attack porphyrias
severe congenital porphyrias
what are the more common features of skin porphyrias
skin blistering and fragility, and acute phototoxicity
how common are skin porphyrias in Scotland
rare
most common is porphyria cutanea tarda which is 1 in 13,000 people
which enzyme has reduced activity in porphyria cutanea tarda(PCT)
uroporphyrinogen synthase
what type of porphyria is porphyria cutanea tarda(PCT)
hepatic(problem mainly in liver)
what are the clinical features of porphyria cutanea tarda (PCT
typical; blistering(unilocular), fragility
also; hyperpigmentation, hypertrichosis, solar urticaria, morphoea
what investigation is used for PCT
woods lamp
what are the aims of treatment of PCT
relive the skin disease, treat underlying disease
what are some underlying causes of PCT
alcohol, viral hepatitis, oestrogens, haemochromatosis
what enzyme has reduced sensitivity in erythropoietic protoporphyria and what does it cause
ferrochelatase has reduced sensitivity, causes build up of protoporphyrin
what inheritance pattern is seen in erythropoietic protoporphyria
autosomal dominant
what is involved in the clinical presentation of erythropoietic protoporphyria
irritation + burning pain on skin(non-blistering) on exposure to sunlight
what investigations are used for diagnosis of erythropoietic protoporphyria
fluorescence of peripheral RBCs and detection of increased protoporphyrin in RBCs and stool
what is involved in the management of erythropoietic protoporphyria
6 monthly LFTs and RBC porphyrins, and visible light photoprotection measures
also prophylactic UVB phototherapy and anti-oxidants can be used
what are some photoprotection measures
behavioural(eg avoid sunlight), clothing, environmental(eg window films), topical sunscreen
