PHOTOSENSITIVITY: IMPORTANT REACTIONS TO LIGHT
The term photosensitivity describes an abnormal response to light, usually referring to ultraviolet radiation (UVR). The two broad types of acute photosensitivity include the following:
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A sunburn type response with the development of morphologic skin changes simulating a normal sunburn—erythema, edema, vesicles, and bullae—as seen in porphyria cutanea tarda and phytophotodermatitis.
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A rash response to light exposure with development of varied morphologic expressions—macules, papules, plaques, eczematous dermatitis, urticaria—as seen in polymorphous light eruption (PMLE), solar urticaria, and eczematous drug reactions to sulfonamides.
The skin response to light exposure is strictly limited to the areas that have been exposed, and sharp borders are usually noted.
It should be noted that sparing of certain skin areas may provide the clue to photosensitivity—the upper eyelids (which are obscured when the eyes are open normally), the skin on the upper lip and under the chin (submental area), a triangle behind the ears, the skin under a watchband, the area covered by a bathing suit, and the skin in body creases on the back and sides of the neck or abdomen.
A sunburn is an acute, delayed, and transient erythema of the skin following exposure to UVR emitted from sunlight or artificial sources. Sunburn is characterized by erythema and, if severe, by vesicles and bullae, edema, tenderness, and pain.
UVR sunburns can be divided into UVB (290–320 nm) erythema, which develops in 12 to 24 hours and fades within 72 to 120 hours, and UVA (320–400 nm) erythema, which peaks between 4 and 16 hours and fades within 48 to 120 hours.
AGE All ages. Infants have an increased susceptibility.
GENDER M = F.
PHOTOTYPES Most frequently seen in skin phototypes (SPT) I, II, and III (Table 16-1).
| Skin Phototype | Reactivity to UVR | Phenotype Examples |
|---|---|---|
| I | Almost always sunburns, never tans | White skin, blond hair, blue or brown eyes, freckles |
| II | Usually sunburns, tans with difficulty | White skin; red, blond, or brown hair, blue, hazel or brown eyes |
| III | Sometimes sunburns, can tan gradually | White skin, any color hair, any color eyes |
| IV | Occasional sunburns, tans easily | White or brown skin, dark hair, dark eyes |
| V | Rarely sunburns, tans well | Brown skin, dark hair, dark eyes |
| VI | Almost never sunburns, tans well | Dark brown or black skin, dark hair, dark eyes |
RACE Caucasian > Asian, American Indian > Black. Individuals with light skin, blue eyes, and blond/red hair are at greatest risk of sunburn.
ETIOLOGY Overexposure to UVB (290–320 nm) leads to erythema and edema. The skin reaction can be augmented by photosensitization drugs or chemicals (psoralens, sulfonamides, tetracyclines, doxycycline, etc.). The intensity of UVR is augmented by reflective surfaces (snow, sand, water), altitude, and latitudes near the equator. UVB is most intense during the midday hours of 10 AM to 4 PM.
GENETICS SPTs are genetically determined.
Sunburn-induced erythema and edema are mediated by prostaglandins, nitric oxide, histamine, and arachidonic acid. Systemic symptoms are mediated primarily by interleukins and other proinflammatory cytokines.
Mild reactions to sunlight begin 6 to 12 hours after the onset of exposure, peak at 24 hours, and fade within 3 to 5 days. Sunburns have a similar time course with blister formation on day 2 and desquamation on resolution. The skin usually is pruritic, painful, and warm to touch. Severe sunburn over large surfaces creates fever, chills, malaise, and even prostration.
TYPE OF LESION Macules, plaques, vesicles, and bullae (Fig. 16-1).
COLOR Bright red.
PALPATION Edematous areas are raised and tender.
DISTRIBUTION Confined to areas of exposure (rarely in covered areas, depending on the degree of exposure and the SPT of the person).
SEVERE CASES “Toxic” appearance: Fever, weakness, tachycardia may be present.
DERMATOPATHOLOGY Necrotic keratinocytes (“sunburn cells”) in the epidermis with exocytosis of lymphocytes and vacuolization of melanocytes and Langerhans cells. In the dermis, there is vascular dilation, perivascular edema, and perivascular inflammation.
Sunburns are a normal reaction of the skin to UV radiation overexposure, but airborne contact dermatitis, other photoreactions, lupus erythematosus (LE), and medication-induced photosensitivity should also be considered. Early in life, the initial presentations of photosensitivity disorders such as porphyria cutanea tarda or xeroderma pigmentosum may present with a sunburned appearance.
Sunburns self-resolve over 2 to 4 weeks and scarring rarely results. Rarely, permanent hypomelanosis due to the destruction of melanocytes may occur.
Photoprotection from UVA and UVB is helpful. Symptomatic treatment includes cold compresses, colloidal oatmeal baths, calamine lotion, aloe-based moisturizers, emollients (hydrated petrolatum, Vaseline), topical steroids, NSAIDs, and antihistamines. Severe cases may require systemic steroids (prednisone or methylprednisolone).
Solar urticaria is a distinctive reaction pattern of wheals that develops within minutes after exposure to sunlight or artificial UVR and disappears within 24 hours.
AGE Any age. More common between 30 and 50 years.
GENDER F > M, 3:1.
INCIDENCE 3/100,000.
ETIOLOGY Most likely type 1, IgE-mediated hypersensitivity reaction directed against a specific photoallergen in susceptible individuals.
Solar urticaria may be induced by several different mechanisms. Some patients with solar urticaria have an inborn error of protoporphyrin metabolism. Others demonstrate passive transfer and reverse passive transfer tests supporting an allergic mechanism. For many, the mechanism is still unknown.
In solar urticaria, the patient experiences itching and burning that occurs within a few minutes of exposure to sunlight. Soon after, erythema and wheals appear only in the sites of exposure. The wheals disappear within several hours. Severe attacks can be associated with an anaphylactic-like reaction with nausea, headache, bronchospasm, and syncope.
TYPE Urticarial wheals (Fig. 16-2).
COLOR Pink, red.
DISTRIBUTION Routinely covered areas (arms, legs, and trunk) > chronically exposed areas (face and dorsa of the hands) due to skin “hardening” in areas of chronic exposure.
DERMATOPATHOLOGY Mild nonspecific changes: vascular dilatation, dermal edema, and periVascular inflammation.
PHOTOTESTING Phototesting is helpful in discovering the wavelengths involved, and can aid in the management of the disorder. Solar urticaria has been classified into several types depending on the action spectrum that elicits the eruption: UVB, UVA, and visible light, or a combination of these.
Solar urticaria can be confused with PMLE, photoallergic drug reactions, or other urticarias.
Solar urticaria typically undergoes spontaneous remission. Fifteen percent of patients are symptom-free after 5 years and 25% of patients are symptom-free after 10 years. Most individuals report some improvement in their symptoms over time even if complete resolution does not occur.
Photoprotection with sun blocks and sun avoidance is helpful. Symptomatic treatment includes antihistamines (diphenhydramine, hydroxyzine, cetirizine). For severe or refractory cases, systemic steroids, antimalarials, intravenous immunoglobulin (IVIG), cyclosporine, omalizumab, extracorporeal photopheresis, or plasmapheresis may be necessary. Desensitization can be attempted with the specific wavelength light treatments with or without psoralens to slowly increase UVR tolerance (“hardening”).
PMLE is the most common type of photodermatosis characterized by monomorphous macules, papules, plaques, or vesicles within a few hours of sun exposure (UVB, UVA, and rarely, visible light).
INSIGHT 
While PMLE can manifest differently between patients, an individual patient usually manifests with the same morphology after each exposure.
SYNONYMS Sun allergy, sun poisoning, benign summer light eruption, juvenile spring eruption.
AGE Any age. Average age of onset: 20 to 30 years.
GENDER F > M.
INCIDENCE 22% in Scandinavia, 15% in the United States, 5% in Australia.
RACE All races.
GENETICS Up to 70% of the population has a tendency to develop PMLE, but with variable penetrance. Increased incidence of PMLE in twins and in individuals with a family history suggests an as-yet undetermined specific genetic susceptibility.
The relation of the eruption to ultraviolet exposure is unknown. A delayed hypersensitivity reaction to an antigen induced by UVR is possible. UVA, UVB, and visible light have all been reported to trigger PMLE flares.
PMLE comes on suddenly, following minutes to days of sun exposure. The rash most often appears in vacationing persons with an acute intense exposure to sunlight. The rash appears within 18 to 24 hours after exposure and, once established, persists for 7 to 10 days, thereby limiting the vacationer’s subsequent time spent outdoors. PMLE appears in spring or early summer, but will resolve by fall, suggesting a hardening response to UVR.
TYPE Papules, macules, vesicles, plaques (Fig. 16-3). In a given individual, one morphology tends to be dominant.
COLOR Pink to red.
SIZE 2 to 3 mm to >1 cm.
DISTRIBUTION Face (helices of ears), V of neck, outer arms, dorsal hands > covered areas (trunk).
Fever, malaise, headache, nausea are rare. Pruritus may also be present.
DERMATOPATHOLOGY Skin biopsy shows epidermal edema, spongiosis, vesicle formation, and mild liquefaction degeneration of the basal layer, but no atrophy or thickening of the basement membrane. A dense lymphocytic infiltrate is present in the dermis, with edema and endothelial swelling.
PMLE can be difficult to distinguish from LE, solar urticaria, porphyrias, light-exacerbated atopic or seborrheic dermatoses, or erythema multiforme.
The course is chronic and recurrent and may, in fact, worsen each season. Although some patients may develop “tolerance” by the end of the summer, the eruption usually recurs the following spring, and/or when they travel to tropical areas in the winter. However, spontaneous improvement or even cessation of eruptions can occur in 75% of patients after 30 years.
To prevent PMLE, sunscreens and sun avoidance are recommended. Topical self-tanning products can help build a tan to prevent PMLE. In severe cases, phototherapy (narrow-band UVB or PUVA), systemic β-carotene, antimalarials (hydroxychloroquine, chloroquine), azathioprine, or cyclosporine can be helpful.
After PMLE occurs, symptomatic relief may be obtained with topical steroids. In severe cases of PMLE, oral steroids (prednisone or methylprednisolone) may be necessary.
Hydroa vacciniforme (HV) is a chronic disease of childhood, of unknown etiology, characterized by recurrent vesicles on sun-exposed skin that heals with “vacciniform” scarring.
SYNONYM Bazin’s HV.
AGE 3 to 15 years.
GENDER M > F.
INCIDENCE 0.3/100,000.
RACE Caucasians, Asians > darker skin types.
GENETICS Rare familial cases reported.
ETIOLOGY Unknown.
The pathogenetic mechanism for HV is unknown, and it may be a more severe scarring form of PMLE. Epstein–Barr virus has been detected in some patients. Summer UVA exposure is causal.
Burning, itching, stinging macules, and papules occur on sun-exposed sites 30 minutes to 2 hours after sun exposure. The papules then progress to vesicles, which umbilicate and form hemorrhagic crusts. One to two weeks later, the crusts heal with vacciniform scars. Mild fever and malaise may accompany the rash.
TYPE Papules, vesicles, hemorrhagic crusts, scars (Fig. 16-4).
COLOR Pink, red, hyper- and hypopigmentation.
DISTRIBUTION Face, dorsa of hands.
NAILS Photoonycholysis.
OCULAR Keratoconjunctivitis, corneal clouding, keratitis.
SKELETAL Bone/cartilage destruction in severe HV.
The differential diagnosis for HV includes varicella, porphyrias, PMLE, and LE. Rarely, HV-like lesions have been reported as a manifestation of EBV-associated lymphoproliferative disorders in individuals with accompanying lymphadenopathy and systemic symptoms.
DERMATOPATHOLOGY Epidermal vesicles and confluent epidermal necrosis with a dense perivascular, lymphocytic infiltrate.
HV has a good prognosis and typically self-resolves during adolescence. Patients are most affected by the scarring.
There is no specific treatment for HV, and the disease self-resolves with age. Management includes sun avoidance, regular use of sunscreens, and sun-protective clothing. For severe HV, phototherapy (BB-UVB, NB-UVB, or PUVA), systemic antimalarials, β-carotene, thalidomide, azathioprine, cyclosporine, or fish oil supplementation may be helpful.
Phytophotodermatitis is a streaky hyperpigmentation of the skin caused by contact with certain (furocoumarin-containing) plants and concomitant exposure to sunlight.
SYNONYMS Plant-induced photosensitivity, berloque dermatitis, Berlock dermatitis.
AGE Any age.
GENDER M = F.
INCIDENCE Common.
ETIOLOGY Furocoumarin compounds in specific plants (parsley, celery, parsnips, lime, lemon, fig, mango, carrots, dill, meadow grass) get onto (topically) or into (by ingestion) the skin. Subsequent sunlight exposure results in photosensitive dermatitis.
The child usually gives a history of playing in grassy meadows or beach grass, making lemonade or limeade, followed the next day by the appearance of a streaky, erythematous (sometimes blistering) pattern leaving a residual hyperpigmentation.
TYPE Macules, vesicles, bullae.
SHAPE Bizarre streaks, artificial patterns that indicate an “outside job” (Fig. 16-5).
DISTRIBUTION Areas of contact: arms, legs, and face.
Phytophotodermatitis can sometimes be mistaken for child abuse with the linear hyperpigmented streaks of pigment being mistaken for resolving bruises.
Most episodes of phytophotodermatitis fade spontaneously, but the pigmentation may last for weeks.
Phytophotodermatitis is best managed by identifying and avoiding furocoumarin-containing culprits in the sun. For symptomatic relief of acute lesions, a short course of topical steroids or cooling moisturizers such as calamine or aloe may be useful. The postinflammatory hyperpigmentation will gradually fade over a period of weeks to months.
DRUG-INDUCED PHOTOSENSITIVITY
Drug-induced photosensitivity describes an adverse reaction of the skin that results from simultaneous exposure to certain drugs (via ingestion, injection, or topical application; Tables 16-2 and 16-3) and UVR or visible light. The chemicals may be therapeutic, cosmetic, industrial, or agricultural. There are two types of reaction: (1) phototoxic, which can occur in all individuals and is essentially an exaggerated sunburn response (erythema, edema, vesicles, etc.) and (2) photoallergic, which involves an immunologic response in a susceptible individual with a resultant rash.
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