Photodermatology Flashcards
benefits of UV light
photosynthesis vit D synthesis heat vision circadian rhythms bactericidal therapeutic and diagnostic use
hazards of sunlight exposure
sunburn - eyes skin cancer photoageing photosensitivity
types of UV light
UV A, B, C
Ozone absorbs which UV ?
C and part of B
therefore we are exposed to UVA and some UVB
UVC has the shortest wavelength, true or false
true
which UV is more likely to produce sunburn
UVB
sources of UV light
sun
artificial - therapeutic, sunbeds
what light do sunbeds emit
fluorescent UVA and <1% UVB
what types of light can be used in phototherapy
UVB - narrow band
UVA
what is PUVA
photochemotherapy
Psoralen + UVA = PUVA
sensitise skin with psoralen and then irradiate skin with UVA
risk of skin cancer therefore UVB is trialled first and PUVA is last line
how many types of Fitzpatrick skin type are there
1-6
describe the Fitzpatrick skin types
1 - pale, always burns 2 - burns but can tan 3 - tans but can burn 4 - tans 5 - brown skin 6 - black skin
what actually happens in sunburn
keratinocyte apoptosis
what causes sunburn and when is the onset and peak of symptoms
UVB
onset 2-4h
peak 12-24h
onset and peak of PUVA erythema
onset 24h
peak 96h
what causes UVB erythema
prostaglandins
what causes UVA erythema
oxygen
what are other consequences of sunburn
immunosuppression
- langerhans cell migration
- suppression of delayed hypersensitivity
cumulative sun damage causes SCC/BCC?
SCC
acute sunburns causes NMSC/MSC
melanoma skin cancer
what is the mechanism of photoageing
solar elastosis
what is the commonest caucasian skin cancer
BCC / rodent ulcer
causes of photodermatoses
idiopathic genetic chemical photosensitivity - exogenous - endogenous
features of polymorphic light eruption PLE
very common young women type 4 hypersensitivity few hours of sun exposure results in erythematous papules and vesicles on areas that are generally not exposed to the sun resolve over few days without scarring Mx - UVB desensitisation 'hardening'
what test can provoke PLE if unsure of the diagnosis
UVA
what is actinic prurigo
rare childhood onset F>M FH affects eyes, lips, end of nose resolution by adulthood
what is solar urticaria
rare
persistent, immediate and severe onset
abnormally sensitive to UVA and visible wavelengths
type 1 hypersensitivity
what is chronic actinic dermatitis
common Males over 50 photoexposed site eczema broadband photosensitivity background atopic eczema and CAD e.g. plants Type 4 hypersensitivity
example of genetic photodermatoses
xeroderma pigmentosum
what is xeroderma pigmentosum
AR inheritance failure of DNA excision repair mechanisms rapid photoageing of skin development of skin cancers in childhood death in teens
causes of drug induced photosensitivity
psoralens - lime, celery, parsley antibiotics - sulphonamides, tetracyclines, fluoroquinolones diuretics - thiazides, furosemide NSAIDs quinine amiodarone
what UV light mediates drug induced photosensitivity
UVA
example of endogenous chemical photosensitivity
porphyrias
example of an inherited porphyria
erythropoeitic protoporphyria EPP
examples of acquired porphyria
porphyria cutanea tarda PCT
causes of PCT
haemochromatosis
viral hepatitis
increased oestrogen
alcohol
what are photoaggravated dermatoses
give examples
skin disease which is aggravated but not caused by sunlight
eczema, psoriasis, SLE, rosacea, pemphigoid, pemphigus, EM
mainstay investigations for photodermatoses
monochromator phototesting provocation test MED test photopatch tests porphyrins, lupus studies HLA histology
management options
phototherapy
PUVA
laser
PDT
what is photodermatology
study of the interaction between non-ionising radiation and the skin
types of sunscreen
reflectant - very thick
chemical - absorb
