Photosensitive Dermatitis

1

What is “photosensitivity”?

Photosensitivity is defined as development or exacerbation of a skin eruption and/or skin symptoms (such as pruritus or pain) after exposure to light (particularly to sunlight, but possibly due to an artificial light source of similar wavelength). Admittedly, the patient may not always directly relate an eruption to light exposure, and there may also be a delay in the onset of signs or symptoms following light exposure. Ergot, when a skin eruption is “photodistributed” (see below), even without a definite history of exacerbation after light exposure, many dermatologists classify it as a probable “photodermatosis.” Some photosensitivity reactions may simply appear as a “sunburn,” but the reactions occur with lesser light exposure than would normally be required to induce a sunburn.

Santoro FA, Lim HW. Update on photodermatoses. Semin Cutan Med Surg. 2011; 30:229–238.

2

What is the clinical appearance of a “photodistributed” eruption?

A “photodistributed” eruption affects the skin of the sun-exposed face, the distal/lateral forearms, the dorsal hands, a V-shaped area of the upper chest (where collars open), the lateral and posterior neck, and any other area exposed to visible light (typically the sun). Such eruptions usually spare the upper eyelid, the skin beneath (in the shadow of) the nose and lower lip, the neck beneath the chin (in shadow), and inner arms, the upper thigh, and other clothing-protected sites. In “photocontact processes” the reaction appears in a similar distribution, but it is due to both exposure to a photoactive chemical and light, together.

3

What is the difference between a phototoxic reaction and a photoallergic reaction?

A “phototoxic” reaction ( Fig. 17.1 ) is an exaggerated sunburn-type reaction, where skin cells are damaged directly by light/ultraviolet light through the production of free radicals, toxic metabolites, heat, or by direct damage to DNA, augmented by external chemicals. Phototoxic reactions occur within minutes to hours of exposure, although on occasion, the reaction is delayed for a day or two. A phototoxic reaction does not involve an immune hypersensitivity, and it can be produced in anyone with the appropriate dose of a chemical and light/ultraviolet light. It can happen on first exposure without prior sensitization. Phototoxic reactions are well demarcated.

A photoallergic reaction occurs only in previously sensitized individuals light/ultraviolet light, interacts with an endogenous ( Fig. 17.2 A ) or exogenous ( Fig. 17.2 B) chemical, converting it to an allergen that the immune system recognizes, prompting a further immune-mediated response. Photoallergic reactions usually occur 1–3 days after exposure (with the exception of solar urticaria, which is nearly immediate). Photoallergic reactions are photodistributed, but may extend to covered areas or even distant sites due to “autoeczematous (id)” phenomenon.

Sometimes, chemicals may produce both a phototoxic and photoallergic reaction.

4

Name some common topical phototoxic and photoallergic agents and the action spectra

Almost all topical phototoxic and photoallergic reactions are caused by ultraviolet A (UVA) light and, less often, ultraviolet B (UVB) or visible light. Some of the most common topical agents are listed in Table 17.1 .

5

Name common systemic phototoxic and photoallergic agents and their action spectra

As in the case of the topical agents, the action spectrum for almost all systemic phototoxic and photoallergic reactions is UVA, rarely UVB or visible light. Some of the most common systemic agents are listed in Table 17.2 .

Stein KR, Scheinfeld NS. Drug-induced photoallergic and phototoxic reactions. Expert Opin Drug Saf. 2007; 6:431–443.

6

Give some examples of unique phototoxic/photoallergic reactions

• Pseudoporphyria (nonsteroidal antiinflammatory drugs [NSAIDs], especially naproxen).

• Photo-onycholysis (tetracyclines, fluoroquinolones, diuretics, NSAIDs, and psoralens).

• Hyperpigmentation (amiodarone, tricyclics, diltiazem, minocycline, hydroxychloroquine, gold, silver).

• Lichenoid eruptions (quinine, quinidine, gold, hydrochlorothiazide, calcium channel blockers).

• Phytophotodermatitis (furocoumarins in lime juice, parsley, celery, parsnips, some grasses).

• Radiation recall reaction (methotrexate given after radiation or sunburn, which reproduces or exaggerates the original burn reaction).

7

What are some scenarios in which the skin may be more sensitive to ultraviolet radiation?

• Isotretinoin and retinoids (due to thinning of the stratum corneum).

• 5-Fluorouracil (due to the antimetabolite affecting DNA repair).

• Methotrexate (due to antimetabolite affecting enzymatic recovery after UV damage).

8

What are important questions to ask a patient with a suspected photosensitivity reaction?

• How long does it take for the skin reaction to develop following light exposure? Some reactions (solar urticaria) occur within minutes of sun exposure, while others may take days, hours, or weeks to develop.

• Have you ever had a similar skin reaction to light? Some light-induced conditions, such as polymorphous light reaction (PMLE), tend to be recurrent and seasonal, while others may be one-time events.

• Is there a family history of skin reactions to light? Some photosensitivity disorders are familial (erythropoietic protoporphyria) or occur more often in certain ethnic groups (actinic prurigo of Native Americans).

• What skin products do you use? Numerous products (soaps, perfumes, sunscreens) may produce a photoallergic contact dermatitis in certain individuals.

• What oral medications do you use? Numerous drugs, prescription and nonprescription, can produce photosensitive reactions.

• Do you have itching or pain? Pruritus is common with some conditions, such as photoallergic contact dermatitis, while pain or burning is more often associated with phototoxic disorders and some porphyrias.

• Do you have any other symptoms? Some photosensitive dermatoses are limited to the skin, but others, such as systemic lupus, may be associated with internal involvement.

9

What are the most common causes of photosensitive dermatoses?

Medications, both systemic and topical, can cause photosensitivity. Polymorphous light eruption is the most common photodermatitis, and it appears to have a hereditary element.