Photodermatoses Flashcards
What is photo dermatology
The interaction between non-ionising radiation and the skin - includes UV
Also includes the use of light radiation for diagnostic and therapeutic cases
What is the Fitzpatrick scale
A scale of skin types by how photosensitive they are
Dependent on the level of melanin
Class 1 is most likely to burn etc
Class 6 is black skin
What is the cause of many porphyrias
A defect in one of the enzymes in the haem pathway
Leads to a build up of porphyrins
Different enzyme defects cause different types
What are the 4 main groups of porphyrias
Photo toxic skin porphyria - erythropoietic
Blistering and skin fragility porphyria
Acute attack
Severe congenital
How do you diagnose porphyria cutanea tarda
Look for clinical signs - blisters, fragile skin (often on backs of hands) in response to sun exposure
Plasma scan - will show abnormal porphyrins
Take a urine sample and shine a woods lamp through it - the excess porphyrins cause it to go a different colour
What are some non-skin affects of erythropoietic protoporphyria
Mild anaemia
Gallstones
Rarely liver failure
What investigations can be done for EPP
Quantative RBC porphyrins
Transaminases
Flurocytes
What can be done to manage EPP
Genetic counselling and advice on condition
6 months of LFT and RBC porphyrin checks
Protection from visible light - long, dark clothing etc
Phototherapy - exposure to build tolerance
Anti-oxidants
List some protective measures from UV light
Behavioural - avoiding midday
Clothing
Environmental - staying in shade, having blinds drawn
Sunscreen
What are the benefits of UV exposure
Vitamin D synthesis - sun is our main source Heat Vision Circadian rhythms Bactericidal Therapeutic & diagnostic use
What are the risks of UV exposure
Sunburn Eyes - conjunctivitis, keratitis, cataract (only visible light reaches retina) Skin cancer - BCC, SCC, melanoma Photoageing Photosensitivity - photodermatoses
What types of UV reach us on earth
UVA - can get through windows
UVB - only on sunniest days and blocked by glass etc.
UVC is filtered by ozone
Which type of UV is more biologically active - A or B
UVB is more biologically energetic – need less to burn you
What type of UV is used in sunbeds and what are the risks
UVA
Melanoma & non-melanoma skin cancer - complete carcinogen if used regularly before the age of 35
What types of UV are used in therapy
Phototherapy - mainly narrowband UVB
Photochemotherapy - Psoralen + UVA
PUVA
Describe the use of PUVA in skin condiitons
PUVA is used if not responding to other treatments– second line
Give UVA alongside psoralen, a plant based chemical which is good at sensitising to UVA
Allows a small dose of UVA therapy to be effective
Risk of SCC - not used if need many rounds and fair skinned
Describe the onset and peak of UVB sunburn
Onset 2-4 h
Peak 12-24 h
How does UV exposure cause immunosuppression
APC and langerhan’s migrate to the local lymph nodes in response to exposure so the skin loses it immune cells – Won’t mount a proper reaction as fewer cells
May get false negative patch test reactions - delay if patient has been on holiday
UV exposure causes immunosuppression - true or false
True
What is the main genetic photodermatosis and how does it present
Xeroderma pigmentosum
Rare, autosomal recessive
Failure of DNA excision repair - cannot repair sun damage
Rapid photoageing of skin and skin cancer - mel and non-melanoma
Death in teens
What is a polymorphic light eruption
Type IV cell mediated hypersensitivity reaction to sunlight
Develop an itchy rash in sun exposed areas a few hours after exposure
Delayed onset papules & vesicles
Non-scarring
Who gets affected by polymorphic light eruptions
Females
In first 3 decades of life
It is possible for those with polymorphic light eruptions to become desensitised - true or false
True
May not have it forever
How do you differentiate PLE and prickly heat
Prickly heat only in folds
PLE in sun exposed areas
