Photodermatology Flashcards
define photodermatology
the study of the interaction between non-ionising radiation and the skin
list some benefits of UV exposure
photosynthesis vit D synthesis heat circadian rhythm bactericidal therapeutic and diagnostic uses vision
list some hazards of UV exposure
sunburn eyes - conjunctivitis, keratitis, cataracts photageing skin cancer photosensitivity - photodermatoses
What bands of UV radiation pass through the ozone layer, and what bands are completely absorbed by the ozone layer
UVC - all absorbed by the ozone layer
UVB - some absorbed by the ozone layer
UVA - a little absorbed by the ozone layer
What UVR bands are we exposed to on earth
mainly UVA
some UVB
What UVR band is most likely to cause sunburn - UVA or UVB and why
UVB - it is most active
What band of UVR do sunbeds use
Fluorescent UVA
What band of UVR is used in phototherapy
narrow band UVB
In what conditions is UVA phototherapy used to treat
this is a new development for eczema, skin scleroderma
What is photochemotherapy
aka PUVA = psoralen + UVA
what is the role of psoralen
sensitises the skin to UVA
What is used 1st line in therapeutic UVR: UVB phototherapy or photochemotherapy?
UVB phototherapy
why is UVA Tx used second line to UVB phototherapy
with UVA there is an increased risk of skin cancer
How many Fitzpatrick skin types are there
six
Type I Fitzpatrick skin type
only burns
Type II Fitzpatrick skin type
always burns, can tan
Type III Fitzpatrick skin type
tans, can burn
Type IV Fitzpatrick skin type
tans
Type V Fitzpatrick skin type
dark brown skin
Type VI Fitzpatrick skin type
black skin
What happens to cells in the epidermis when someone is sunburned
apoptosis of keratinocytes
Typical duration of onset of UVB “sunburn” erythema
2-4h, peak 12-24h
Typical duration of onset of PUVA erythema
onset 24h, peak 96h
Mediators of UVB erythema
prostaglandins
Mediators of UVA erythema
oxygen
effect of sunlight on the immune system
causes immunosuppression
how does sunlight cause immunosuppression
langerhan’s cell migrate from the BM to draining lymph nodes, and there is suppression of delayed hypersensitivity
why is sunlight causing a suppression of delayed hypersensitivity particularly important?
important in the promotion of carcinogenesis
what is photoageing also called?
solar elastosis
list the 4 different categories of photodermatoses
- Immunological/Idiopathic
- Genetic
- Chemical photosensitivity
- Photoaggravated dermatoses
List the different IMMUNOLOGICAL/IDIOPATHIC photodermatoses
- polymorphic light eruption
- actinic prurigo
- solar urticaria
- chronic actinic dermatitis
- hydroa vacciniforme
what is a polymorphic light eruption (PLE)
after a few hours of sun exposure, papules and vesicles develop, which resolve after a few days without scarring
what type of hypersensitivity reaction is PLE
Type IV
Tx of PLE
watch and wait - will resolve
UVB desensitisation (90% effective)
Ix for PLE
UVA provocation test
what is actinic prurigo
an idiopathic photodermatoses, that occurs in childhood (1st decade) with sore and red papules on the eyes, lips, end of nose that scars
what antigen is associated with actinic prurigo
HLA DR4
what is solar urticaria
an idiopathic photodermatoses that occurs within a few minutes of sun exposure.
what type of hypersensitivity reaction is solar urticaria
type I
Tx of solar urticaria
antihistamines
desensitisation
what is chronic actinic dermatitis
an idiopathic photodermatoses that is essentially pho-exposed site eczema
what type of hypersensitivity is chronic actinic dermatitis
type IV
what bands of UVR is the person sensitive to in chronic actinic dermatitis
broadband - UVA, UVB and visible light
who usually gets chronic actinic dermatitis
old men
list the different GENETIC photodermatoses
xeroderma pigmentosum (the only one we need to know)
what is xeroderma pigmentosum
autosomal recessive disease
- failure of DNA excision repair
presentation of xeroderma pigmentosum
rapid photoageing of the skin and skin cancer
death in teen
what type of skin cancer do people with xeroderma pigmentosum get
both melanoma and non-melanoma
list the different CHEMICAL photodermatoses
exogenous - drugs
endogenous - porphyrias
list the different drugs can induce photosensitivity
psoralens e.g. lime, celery
antibiotics
- sulphonamides
- tetracyclines
- fluroquinolones
diuretics
- thiazides
- furosemide
NSAIDS
Quinine
Amiodarone
What is phytophotodermatosis
a condition in children where they have been exposed to psoralens, then exposed to UVA light
What can phytophotodermatosis be confused with
Non-accidental injury
What is a photoaggravated dermatoses
a pre-existing skin disease that is aggravated by sunlight
List the different PHOTOAGGRAVATED dermatoses
eczema psoriasis rosacea pemphigus, pemphigoid erythema multiforme
What are the mainstay investigations for photodermatoses
monochromator phototesting UVA provocation test MED test (minimal erythema dose test) patch tests HLA status histology
(Depends on individual presentation)
