Photocontact dermatitis and Photopatch testing

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

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

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)

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

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

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

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

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

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

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

UV Dose in cases of photosensitivity Light source 315-400 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

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

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

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

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

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

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

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

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 1985-1990 2859 positive reactions: 28.6% were contact allergy 3.8% classified as photoallergic 1261 patients from 1991-1997 had 1415 reactions 28.7% felt to be contact allergy, 8.1% photoallergic Common reactions seen were topical NSAIDs, disinfectants and phenothiazine

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

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

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

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