Chapter 17 Photosensitive dermatitis
1. What is the definition of photosensitivity?
Although there is not a definition accepted by all, most dermatologists define photosensitivity as the development or exacerbation of a skin eruption and/or symptoms (including pruritus or pain) following exposure to sunlight. In some instances, a patient may not specifically relate the eruption to sun exposure, usually due to a delay in the onset of signs or symptoms following sun exposure. Thus, if a skin eruption is photodistributed, even without a definite history of exacerbation following sun exposure, many dermatologists classify it as a photosensitive dermatosis. Some photosensitivity reactions (e.g., phototoxic drug reactions) are very similar to sunburn but occur with less intense sun exposure than would normally be required to induce sunburn in that individual.
2. What is the difference between a phototoxic reaction and a photoallergic reaction?
A phototoxic reaction (Fig. 17-1) is an exaggerated “sunburn” reaction where skin cells are damaged directly by electromagnetic radiation through the production of free radicals, toxic metabolites, heat, or by direct damage to DNA, augmented by external chemicals. It may occur within minutes to hours of exposure, though it may also be delayed for a day or two. A phototoxic reaction can be produced in anyone given a high enough dose of ultraviolet (UV) light and a phototoxic chemical. It can happen on first-time exposure without a need for sensitization.
Figure 17-1. Phototoxic drug eruption. Sunburn-like erythema on the cheeks, neck, V-area of the chest, and dorsal forearms.
A photoallergic reaction only occurs in sensitized individuals when electromagnetic radiation (usually ultraviolet light, but sometimes visible light) interact with an endogenous (Fig. 17-2A) or exogenous (Fig. 17-2B) chemical, converting it to an allergen that the person’s immune system recognizes as an allergen (requires more than one exposure). Photoallergic reactions typically occur 1 to 3 days after exposure (with the exception of solar urticaria, which is immediate). Phototoxic reactions tend to be well demarcated in the areas of exposure. Photoallergic reactions are also photodistributed, but often have extension of the cutaneous reaction onto covered areas or even distant sites in an autoeczematous type of eruption. Sometimes chemicals may produce both a phototoxic and photoallergic phenomenon.
3. What is the clinical appearance of a photodistributed eruption?
A photodistributed eruption affects the skin in a characteristic distribution, affecting the convex surfaces of face, external areas of forearms and arms, dorsal hands, V-area of upper chest, lateral sides and posterior of neck, and any other area exposed to the sun. It characteristically spares the ocular/eyelid area, beneath the nose and lower lip, inframandibular chin/neck, and inner parts of arms and forearms, and clothing covered sites. In photocontact dermatitis, the affected areas are those areas with exposure to both sunlight and the causative topical agent.
4. Name some of the most common topical phototoxic and photoallergic agents and their action spectrums.
5. Name some of the most common systemic phototoxic and photoallergic agents and their action spectrums.
As in the case of the topical agents, the action spectrum for almost all systemic phototoxic and photoallergic reactions is UVA, rarely UVB and visible light. Some of the most common systemic agents are listed in Table 17-2.
Table 17-1. Topical Agents Causing Phototoxic and Photoallergic Reactions
| PHOTOTOXIC CHEMICALS | PHOTOALLERGIC CHEMICALS |
|---|---|
| Benzocaine Benzoyl peroxide (UVB) Coal tar Erythromycin Halogenated salicylanilides Hydrocortisone Ketoprofen Porphyrins (visible light and UVB) Psoralens |
Sunscreens: oxybenzone, benzophenone, etc. Fragrances: methylcoumarin, musk ambrette, sandalwood oil NSAIDs Oxicams: ampiroxicam, droxicam, meloxicam, piroxicam, tenoxicam Prioprionic acid derivatives: benzophenone, dexketoprofen, ketoprofen, piketoprofen, suprofen (UVA and UVB), tiaprofenic acid, diclofenac Antimicrobials: bithionol, chlorhexadine, fenticlor, hexachlorophene Phenothiazines: chlorpromazine, promethazine Miscellaneous Acyclovir Dibucaine Halogenated salicylanilides (UVA and UVB) Hydrocortisone |
Table 17-2. Systemic Agents Causing Phototoxic and Photoallergic Reactions
| PHOTOTOXIC | PHOTOALLERGIC |
|---|---|
| Antimicrobials Tetracyclines: demeclocycline, dimethylchlorotetracycline, doxycycline, lymecycline, minocycline, tetracycline Quinolones: ciprofloxacin, enoxacin, fleroxacin, levofloxacin, lomefloxacin (UVA and UVB), nalidixic acid, pefloxacin, sparfloxacin Griseofulvin Voriconazole Sulfur-containing medications: bumetanide, furosemide, hydrochlorothiazide, sulfonamides (UVB), sulfonylureas NSAIDs: proprionic acid derivatives: benzophenone, carprofen, ketoprofen, nabumetone, naproxen, suprofen (UVA and UVB), tiaprofenic acid Antimalarials: chloroquine unknown, hydroxychloroquine (UVB), quinidine Miscellaneous: amiodarone, atorvastatin (UVB), calcium-channel blockers, chlorpromazine, prochlorperazine, porphyrins (UVB and visible), psoralens, retinoids (UVA and UVB), St. John’s wart (hypericin) |
NSAIDs: piroxicam, celecoxib, ketoprofen Sulfur-containing medications: hydrochlorothiazide, sulfacetamide (UVB), sulfadiazine (UVB), sulfapyradine (UVB), sulfonamides (UVB), sulfonylureas Antimalarials: chloroquine unknown, hydroxychloroquine (UVB), quinidine, quinine Antimicrobials: chloroamphenicol unknown, enoxacin, lomefloxacin (UVA and UVB), sulfonamides Griseolfulvin Phenothiazines: chlorpromazine, dioxopromethazine, perphenazine, thioridazine Miscellaneous: amantadine, dapsone unknown, diphenhydramine (UVB), flutamide (UVA and UVB), pilocarpine, pyridoxine, ranitidine |
6. Give some examples of unique phototoxic reactions.
• Hyperpigmentation (amiodarone, tricyclics, diltiazem, minocycline, hydroxychloroquine, gold, silver)
