Photobiology and Photosensitive Dermatoses

Question 1

Do shorter or longer wavelengths penetrate skin better.

Answer 1

longer (i.e.. UVA more than UVB)

Question 2

What types of light is sunlight made up from?

Answer 2

infrared light, visible light and ultraviolet light

Question 3

Compare the wavelengths of UVA,B,V rays and how far they penetrate.

Answer 3

UVA 320-400nm penetrates subcutaneous tissue and can destroy elasticity and pigmentary changes

UVB 280-320 penetrates into the dermis resulting in cutaneous erythema and sunburns

UVC 200-280 light absorbed by ozone, impact of penetration has not been determined

Question 4

What is MED?

Answer 4

minimal erythema dose is the minimal amount of UVB wavelength energy to cause skin readiness (varies with individuals)

Question 5

Describe the Fitzpatrick Skin Phototype classifications.

Answer 5

I : always burns, never tans
II: often burns, sometimes tans
III: sometimes burns, always tans
IV: never burns, always tans
V: moderately pigmented skin
VI: darkly pigmented skin

Question 6

What is chromophore?

Answer 6

a biological taste that maximally absorbs energy
ie. UV chromophore: DNA, protein, melanin
Laser chromophore: water, melanin, hemoglobin and tattoo ink

Question 7

What are important things to remember when using phototherapy?

Answer 7

for treatment you must match absorption spectrum of target to laser wavelength for maximum effect

for UVB, must be careful of the delayed effect

cover eyes and genitals

Question 8

What are the immunologic effects of light?

Answer 8

pro-inflammatory (camases released from mitochondria or sunburns)

or

antiflammatory: used as a therapeutic application (increases risk of NMSC, and herpes)

Question 9

Which diseases traditionally respond to phototherapy?

Answer 9

psoriasis, eczema, vitiligo (UVB) and fibrosing diseases and psoriasis (UVA)

NOTE: specifically uses narrow band UVB phototherapy

Question 10

What is a photo toxic reactions and what is its mechanism?

Answer 10

caused by a chemical on the skin or in the body (drug) that reacts with UV light that stimulates the chemical leading to a toxic reaction (no sensitization and red blisters are due to cell death)

Question 11

How is a photoallergic reaction different from a photo toxic reaction?

Answer 11

light alters a chemical in or on the body that then acts as an allergen that stimulates an immune reaction creating a rash that is particularly itchy (this rash requires sensitization); the inflammation is due to lymphocytes, no cell death; is common with sulfa drugs opposed to plants and wide range of drugs

Question 12

What is a polymorphous light eruption?

Answer 12

variable morphology, pruritic rash that is caused by sun exposure, onset is usually in spring among people of norther descent; usually remits with time

Question 13

How would you treat PMLE?

Answer 13

primarily with photo protection although low-dose phototherapy (hardening) can reduce sensitivity, topical steroids or palquenil

Question 14

What is the inheritance and mechanism of xeroderma pigmentosum?

Answer 14

autosomal recessive, caused by a defective DNA nucleotide excision repair

Question 15

What is the risks of XP?

Answer 15

early onset basal and squamous cell carcinomas
increased risk of melanoma and internal malignancies
strict UV avoidance is essential

Question 16

What does SPF mean?

Answer 16

sun protection factor, ratio of the amount of UV light it takes to get burned with the sunscreen vs. without

Question 17

What types of sunscreens are there (mechanism of screening) and what are important things to remember when advising patients on sunscreens?

Answer 17

physical blockers (particles block the light)
chemical blockers (chemical that absorbs the UV spectrum)

remember to get a broad spectrum sunscreen that will block both UVB and UVA rays an SPF between 30-50 and reapply often (1oz= shot glass)