1. Photocontact dermatitis and Photopatch testing

2. Photoinduced skin disease
Autoimmune disease eg. lupus
Metabolic conditions eg porphyria
Internal or external exposure to photoactive agents
Others eg. Polymorphic light eruption
Chronic actinic dermatitis

3. Mechanism of skin disease due to internal or external agents
Phototoxic
Photoallergic
-Some agents can cause both phototoxic and photoallergic reactions

4. Phototoxic Reaction Can occur from first contact
Previous sensitivity not required
Could occur in anyone under certain conditions ie. Sufficient dose/ UV intensity
eg. psoralen exposure, porphyrins, drugs (amiodarone, tetracyclines)

6. Photoallergic reaction
T cell mediated disease.
Requires someone to be sensitised ie. not on first exposure
Usually develops 24 to 72 hours after irradiation
Lower concentrations needed
Requires exposure to agent plus UV exposure
Radiant energy causes modifications within the agent to result in a photo-antigen.
Wavelength of radiation to induce reaction depends on chemical structure of allergen
Diagnosed by photo patch tests

7. Mechanism of a Phototoxic Reaction
Photosensitiser and Radiation (UV) Absorption of Energy Elevation of Molecules to an excited State Photodynamic or non photodynamic reaction Damage to Cell components Inflammation

8. Mechanism of a Photoallergic Reaction
Photoallergen and radiation (UV) Absorption of Energy Elevation of Molecules to an Excited State or binding Generation of a Photoallergen Formation of a Complete Antigen Inflammation by a T cell mediated Immune Response

9. Clinical presentation of Photo induced disease
“Exposure” Pattern distribution
V of neck
Back of hands
Extensor surface of forearms
Sharp cut off for clothing
Sparing of photoprotected areas (under chin and behind ears)
Phototoxic : often resembles sunburn. Limited to exposed areas. Can be bullous/ eczematous

11. Indications for Photopatch testing
Eczematous eruption affecting mainly light exposed sites
Worsening of condition with sun exposure
History of reactions to sunscreens
Suspicion of photoallergic drug eruption

12. Photopatch test Method
Patient seen at day 0
Patch tests allergens applied to back in duplicate one set either side of spine
Use a photopatch test series and also add patient’s own products
Other patch tests may be applied as necessary

14. When is the best time to irradiate the skin?
3 different protocols have been described one of which involves exposure to UV at 24 hours
Retrospective study done in Leeds (Contact Dermatitis 2006). Three sets of allergens applied. Patients had irradiation at 24 hours to one set and 48 hours to another. 48 hours exposure was more sensitive at picking up allergens

15. UV Dose in cases of photosensitivity
Light source nm ie UVA range
Eg PUVA Waldmann 800 canopy
In most cases 5J/cm2
This would not normally induce erythema
If strong suspicion of photosensitivity disorder ideally check MED to UVA initially
Test at 50% MED

16. Day 2 Patient seen for day 2 read
Patches removed and first reading performed
One set (set B) covered with UV protective material
Set A left exposed
UV source- usually UVA flat bed
Dose usually 5J/cm2 at a distance of 15 cm from the back

17. Day 4 Results read at day 4 Interpretation of results
“Crescendo” phenomenon –increasing reaction from 48 hours to 96 hours post exposure - seen in photoallergic
“decrescendo”- reducing/ clearing reaction
Seen in phototoxic

18. SCENARIO 1 Positive result in set A and set B
SCENARIO 1 Positive result in set A and set B. Both reactions of similar intensity  normal allergic contact reaction SCENARIO 2 Positive result in set A and set B. Reaction in set A of greater intensity allergic contact reaction with combined photo contact allergy SCENARIO 3 Negative result in set B. Positive reaction in set A.  photoallergy

19. SCENARIO 4
Both set A and set B negative
SCENARIO 5
General erythema on exposed area
May need to see the patient again on day 7 if nature of allergy not clear

21. What Allergens are Important?
Photoallergic Contact dermatitis is becoming less common
Many common allergens have been withdrawn- particularly fragrance ingredients eg musk ambrette and 6 methyl coumarin- banned by the international fragrance association
Also halogenated salicylanilide and chlorinated phenols previously commonly used antiseptics

22. Sunscreens Increasing use in cosmetics
All agents that absorb UV light can cause contact dermatitis
Eg. Cinnamates, benzophenones, oxybenzones and dibenzoyl methanes
Reflectant sunscreens are not photosensitisers

23. UK Multicentre study BJD 2006
Bryden et al
1155 patients
130 (11.3%) allergic reaction
51 (4.4%) photo contact allergic reaction
64 (5.5%) Contact allergy
15 (1.3%) both contact allergy and photo contact allergy

24. Photopatch Testing of 182 Patients: A 6-Year Experience at the Mayo Clinic Scalf et al Dermatitis 2009;20:44-52
Retrospective study. 54 patients (29.7%) photoallergic contact reactions and 29 (15.9%) had allergic contact reactions to the photoallergy series
Commonest allergens seen were topically applied medications, sunscreen agents (benzophenone 4), fragrances (sandalwood) and antispetics
Photopatch Testing: The 12 year experience of the German, Austrian and Swiss photopatch test group JAAD 2000
1129 patients from
2859 positive reactions: 28.6% were contact allergy
3.8% classified as photoallergic
1261 patients from had 1415 reactions
28.7% felt to be contact allergy, 8.1% photoallergic
Common reactions seen were topical NSAIDs, disinfectants and phenothiazine

25. What allergens should we test?
Sunscreen chemicals
Fragrance ingredients
Drugs
Miscellaneous chemicals

26. Local phototesting series
Sunscreens
Drugs (ketoprofen, etofenamate, piroxicam, benzydamine, promethazine, ibuprofen, diclofenac)

27. Patient Counselling Explain allergens exposure, avoidance
Written information sheets
Advice on suitable alternatives

28. Conclusion Photopatch testing is time consuming and specialised
Uncommon but very important to those affected
Mostly due to sunscreens