Photobiology and Photosensitive Dermatoses

Question 1

Benefits of UV radiation?

Answer 1

visibility, psychological well-being, vitamin D synthesis, establishment of Circadian rhythms.

Question 2

Detrimental effects of UV exposure?

Answer 2

sunburns leading to skin cancer and inflammatory skin disease.

Question 3

Groups of UV light:

Answer 3

UVC (200-280 nm), UVB (280-320 nm), and UVA (320-400 nm). UVA subdivided in the UVA1 (320-340 nm) and UVB1 (340-400 nm).

Question 4

Effects of UVC radiation

Answer 4

Unknown. Most absorbed by ozone

Question 5

Level of UVB absorption

Answer 5

absorbed readily, just below the surface of the skin. Can lead to cutaneous erythema and sunburns.

Question 6

Level of UVA absorption

Answer 6

UVA longer, penetrate deeper, destroy elastin fibers and collagen, leading to wrinkles, loss of elasticity, and pigmentary changes. Responsible for many photosensitive disorders

Question 7

Define minimal erythema dose

Answer 7

Minimal amount of a particular wavelength capable of causing redness of the skin. Varies with skin type.

Question 8

Factors increasing risk of sunburn

Answer 8

direct exposure with sun at peak hours (10 am- 4 pm), higher altitude, reflection from sand and snow. UV can penetrate clouds.

Question 9

Molecule in skin that facilitates light absorption

Answer 9

chromophore (can be selective for UVA or UVB)

Question 10

What type of information about chromophores can be used to help determine which wavelengths should be protected against as tx of specific skin disorders or using UV therapy

Answer 10

peak absorption and a chromophore’s absorption spectrum

Question 11

Effect of UV radiation on DNA

Answer 11

induces mutations that can eventuate into actinic keratosis, basal and squamous cells carcinomas, melanoma. UVB suppresses DNA synthesis, mediating anti-inflammatory effects.

Question 12

Effects of UV radiation on melanin

Answer 12

stimulates melanocytes to give intermediate and delayed tanning. Therapeutic for vitiligo.

Question 13

Laser targets chromophores such as

Answer 13

melanin, Hb, and water to eliminate dyschromia and pigmented skin lesions, telangiectasias, and vascular neoplasms with minimal scarring.

Question 14

Describe the Fitzpatrick skin phototypes

Answer 14

1: always burns, never tans
2: often burns, sometimes tans
3: sometimes burns, always tans
4: never burns, always tans
5: moderately pigmented skin
6: darkly pigmented skin

Question 15

Define intermediate tanning

Answer 15

reactions immediately following UVA exposure, arising from the oxidation of melanin in the skin.

Question 16

Define delayed tanning

Answer 16

from UVB and UVA exposure, peaks after 3 days. Arises from increase in the number of melanocytes, increased melanin synthesis and increased association of melanosomes with keratinocytes.

Question 17

Peak of UVB erythema and recommendations for tx w/ UVB

Answer 17

1000x more erythematous than UVA, peaks 6-24 hours after exposure, so limit tx w/ UVB to at least every other day.

Question 18

Risks associated with indoor tanning

Answer 18

basal and squamous cell carcinomas, melanoma, premature aging, immunosuppression, and cataract formation.

Question 19

Describe the pro-inflammatory vs. anti-inflammatory effects of UV light

Answer 19

Pro-inflammatory: sunburn, phototoxic or photoallergic reactions or photodermatoses
Anti-inflammatory: immunosuppressive, used to treat inflammatory skin diseases like psoriasis and atopic dermatitis, but may increase risk of nonmelanomal skin cancers and reactivation of herpes. Depletes Langerhans cells, cytokines, and T cell activation

Question 20

Define photoxicity

Answer 20

photosensitivity that occurs in any individual based on the amount of allergen to which a person is exposed. Manifested by redness, swelling, and burning. Bullae if severe. Onset w/i hours of exposure, peaks at 24 hours.

Question 21

Medications leading to potential photoxic drug eruptions

Answer 21

amiodarone, doxycycline, furosemide, hydrocholorthiozide, methotrexate, and naproxen.

Question 22

Define phytophotodermatitis

Answer 22

exposure to plant material containing furocoumarins that act as photosensitizers, coupled with UV exposure. Presentation of patchy or linear erythema of uncovered skin. Postinflammatory hyperpigmentation. Common plants: wild parsnip, parsley, celery, lime, lemon, and fig.

Question 23

Define photoallergy

Answer 23

in photoexposed site, delayed onset of 24-72 hours after exposure, requiring a sensitizing episode. HALLMARK: ithcing, redness. Lesions are papular or papulovesicular. Sulfa medication a common cause.

Question 24

Pathology of polymorphous light eruptions

Answer 24

Common in temperate climates, appears in 3rd-4th decade of life. UVA rxn most common, UVB and combination equally less common. Considered a delayed hypersensitivity rxn to unknown antigen. Improves over summer with adaption to UV.

Question 25

Clinical presentation of polymorphous light eruption

Answer 25

Outbreak in spring after UV exposure, itching and burning may develop in minutes, cutaneous lesions w/i hours or days. Light through window or tanning bed give similar effects. Includes itching, edema, pink papules coalescing into plaques and vesicles. Typical sites of upper cheek, nose, chin, back, lateral neck, “v” of chest, outer arms, forearms, shins, dorsal hand, and feet.

Question 26

Tx for polymorphous light eruption

Answer 26

UV minimization, sunblock, photo-protective clothing. Topical corticosteroids to tx inflammation and itching. Low-dose, progressive phototherapy to induce skin “hardening”. May spontaneously improve.

Question 27

Pathology of xeroderma pigmentosum

Answer 27

extreme photosensitivity and high risk of melanoma. Inherited autosomal recessive disease caused by impaired DNA nucleotide excision repair of UV-damage

Question 28

Clinical presentation of XP

Answer 28

Easy sunburns, sometimes with vesiculation noted early. Later develop lentigines (freckles) and xerosis. Basal cell carcinoma and squamous cell carcinoma before age 10, high risk for melanoma. 30% w/ neuro abnormalities, 10-20x increase of internal malignancies (brain, lung, GI, hematopoietic carcinomas). STRICT UV avoidance.

Question 29

Basics of phototherapy

Answer 29

Pt exposed to a series of incrementally increasing doses of UVA or UVB light to promote immunsuppressant effects without risking severe sunburn. Ex: narrow band UVB for psoriasis at 311-313 nm.

Question 30

Medication that increases absorption of UV light and anti-inflammatory effects.

Answer 30

Psoralen, commonly combined with UVA, and available topically (risks inconsistent absorption) or orally (1 hour before UV tx).

Question 31

Risks associated with phototherapy

Answer 31

cataracts (use eye shields), basal cell carcinoma, squamous cell carcinoma, and melanoma. Cover genitals during tx. Get regular skin exams to detect potential cancers.

Question 32

Two types of photoprotection

Answer 32

physical blockers and chemical blockers

Question 33

Physical blockers include:

Answer 33

particles that block UV radiation by surface reflection, like zinc oxide or titanium dioxide. Leave white residue on skin, but now can be micronized to improve absorption.

Question 34

Chemical blockers:

Answer 34

contain agents that absorb UV light and disperse it as heat. Can be specific to UVA or UVB.

Question 35

UVA blockers:

Answer 35

benzophenones (oxybenzone, can cause photoallergic rxn), avobenzone (effective up to 400 nm, but photolabile), titanium dioxide/zinc oxide, mexoryl

Question 36

UVB blockers:

Answer 36

Para-aminobenzoid acid (PABA), Padimate O (less sensitizing, less likely allergic contact dermatitis than PABA), salicylates (improve stability of other agents), cinnamates (easily sweat off), titanium dioxide/zinc oxide.

Question 37

Sun protection factor

Answer 37

ratio of time to development of the minimal erythema dose compared to onset of erythema in unprotected skin. SPF= MED protected/MED unprotected. Measures UVB only.

Question 38

Broad-spectrum sunscreen

Answer 38

Must cover UVB and UVA. Can’t be labelled as “sunblock” or “waterproof”

Question 39

Suggestions for photoprotection

Answer 39

Use broad-spectrum UVB and UVA sunscreen, apply 30 minutes prior to exposure, proper quanitity is 1 oz, reapply every 2 hours or if sweating or swimming, clothing and hats for further protection, minimize exposure in peak hours, avoid tanning beds, snow reflects up to 80% of UV light, 80% UV light goes through clouds.

Question 40

Vitamin D controversy

Answer 40

No safe amount of UV light to get proper vitamin D and not get malignancies. Get Vitamin D from diet (according to American Academy of Dermatology).