Phytophotodermatitis

Background

Phytophotodermatitis (PPD) is a cutaneous phototoxic inflammatory eruption resulting from contact with light-sensitizing botanical substances, also known as furanocoumarins, and long-wave ultraviolet A (UV-A, 320-380 nm) radiation. Psoralen is the particle that is active in furanocoumarins.^[1] Furanocoumarins, present in some plants (eg, parsley, celery, carrots, limes), react using their parent compound, psoralen, with the UV radiation, which forms the eruptions on the skin.^[2] The eruption usually begins approximately 24 hours after exposure and peaks at 48-72 hours.^[3] The incidence rate is unknown.^[1] More serious conditions should be ruled out.^[1] The occurrence of the rash requires exposure to furanocoumarins and sunlight, and it is a direct phototoxic reaction entirely independent of the immune system.^[4] The phototoxic result may be intensified by wet skin, sweating, and heat. The onset of the rash may be delayed and may not occur immediately after exposure to all of the elements.^[5] Once the rash does occur, it may take weeks to resolve.^[5]

Phytophotodermatitis typically manifests as a burning erythema that may subsequently blister. Postinflammatory hyperpigmentation lasting weeks to months may ensue (see the images below). In some patients, the preceding inflammatory reaction may be mild and go unrecognized by the patient. In this case, the patient presents with only pigmentary changes. Pain may be associated with the blister, resulting from necrosis of the affected epidermis.^[4] The rash typically is nonpruritic, and if pruritus occurs, then further investigation into alternative diagnoses should be considered.^[1]

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A 26-year-old female airline flight attendant exposed to lime while serving drinks en route to the Caribbean. During the Caribbean layover, she had si....

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The 2-month follow-up picture of a patient with a drip-pattern blister formation on the dorsal forearm demonstrates the potential postinflammatory pig....

See 11 Common Plants That Can Cause Dangerous Poisonings, a Critical Images slideshow, to help identify plant reactions and poisonings.

Also see Berloque Dermatitis and Drug-Induced Photosensitivity.

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Pathophysiology

Cutaneous inflammation produced by plants can be separated into 4 groups based on their specific mechanism of action: urticarial dermatitis, irritant contact dermatitis, allergic contact dermatitis, and phototoxic dermatitis.

Phytophotodermatitis is a phototoxic reaction entirely independent of the immune system. In other words, phytophotodermatitis can occur in any individual, and prior sensitization or an intact immune system is not required. The ingredients needed to produce phytophotodermatitis include temporal exposure to both a photosensitizing substance, such as psoralens, and ultraviolet radiation. Furocoumarins are photosensitizing chemical components produced by certain plants and consist of psoralens, 5-methoxypsoralens, 8-methoxypsoralens, angelicin, bergaptol, and xanthotal.

The natural sunlight emission spectrum reaching the earth ranges from approximately 270-5000 nm. This electromagnetic radiation consists of photons with a reciprocal relationship between the wavelength and the energy of the photons. Only light that is absorbed into the skin can cause a photochemical reaction. Within the light spectra, UV-A (320-400 nm) is responsible for the vast majority of photoreactions resulting in phytophotodermatitis.

The wavelengths of ultraviolet light that most efficiently produce phytophotodermatitis lie within the UV-A range and have peak activity at 335 nm. When a photon with the appropriate wavelength strikes a furocoumarin, the energy is absorbed, raising this chemical to a triple excited state from the ground state. Upon return to the ground state, energy is released in the form of heat, fluorescence, and/or phosphorescence, and a photoproduct may form.

Two distinct photochemical reactions have been described in phytophotodermatitis, which occur independently from each other. A type I reaction occurs in the absence of oxygen, whereas a type II reaction occurs in the presence of oxygen. These photochemical reactions damage cell membranes and DNA and result in DNA interstrand cross-linking between the psoralen furan ring and the thymines or the cytosines of DNA. During the type I oxygen-independent reaction, the RNA and nuclear DNA become fastened to the exposed ultraviolet-activated furocoumarins. Likewise, the oxygen-dependent reactions result in cell membrane damage and edema from activated furocoumarins. This results in activation of arachidonic acid metabolic pathways and in cell death (sunburn cells and apoptotic keratinocytes). Clinically, erythema, blistering, epidermal necrosis, and eventual epidermal desquamation occur. See the image below.

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Close-up view of vesicular linear streaks with morphology suggestive of scattered foci of epidermal necrosis.

A postinflammatory pigment alteration may follow the acute phase of this phototoxic reaction. This alteration occurs primarily by 2 mechanisms. First, melanin, which is normally found in the epidermis, "falls" into the dermis and is ingested by melanophages. Secondly, an increased number of functional melanocytes and melanosomes are distributed in the epidermis following phytophotodermatitis and also account for the hyperpigmentation. This hyperpigmentation may serve as a protective mechanism against further UV injury. Clinically, this corresponds with irregular hyperpigmentation (or occasionally hypopigmentation resulting in dyschromia) seen as the end stage of the phototoxic reaction.

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Etiology of Phytophotodermatitis

The most common plant family to cause phytophotodermatitis is the Umbelliferae family. See the images below.

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Queen Anne's lace, a member of the Umbelliferae family of plants, is well known to produce a furocoumarin-induced phototoxic eruption.

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Ficus. The common fig contains furocoumarins and should be considered amidst the list of potential offending agents that cause phytophotodermatitis.

Phytophotodermatitis is most commonly caused by ingestion of or topical exposure to psoralens (furocoumarins). Psoralens have been isolated from at least 4 different plant families: Umbelliferae,^[6] Rutaceae,^[7] Moraceae, and Leguminosae.

Table. Common Causes of Phytophotodermatitis

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See Table

Chart modified from Plants and the Skin. 1993:70-71.^[11]

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Epidemiology

Frequency

The overall incidence of phytophotodermatitis is unknown, but it undoubtedly varies according to the population studied and is based on the risk of exposure to psoralen compounds. Because furocoumarins are found in a wide range of wild and domestic plants, a variety of patient groups may become exposed. An example of an international greenery known to produce phytophotodermatitis is Ficus carica, also known as a fig tree. This plant is often sought for the fruit it produces, as well as for analgesic folk medicine applications. Ficus pumila can be found worldwide, yet is native to China, Japan, and Taiwan.

Race

Any race may be affected, but phytophotodermatitis is most easily recognized in fair-skinned patients.

Sex

Both sexes may be affected.

Age

Any age may be affected, but note that phytophotodermatitis occurring on a child may be mistaken for child abuse. Classic examples include a handprint pattern on a child after exposure to a parent cooking with lime juice or a linear drip pattern on a child's hands and arms after eating real juice ice pops.

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Prognosis

The prognosis is good with identification and avoidance of the offending agent. Most commonly, phytophotodermatitis is a localized cutaneous phenomenon resulting initially in a burning sensation, which may be followed acutely by erythema and blistering. Eventually, the affected sites may desquamate and develop permanent hyperpigmentation or hypopigmentation. However, scarring is rare.

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Patient Education

Reassure the patient that phytophotodermatitis is a self-limited problem that resolves with removal of the offending agent.

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History

Phytophotodermatitis (PPD) has been recorded for thousands of years and can be dated back through Egyptian history. It may be seen described in the Ebers Papyrus and was mistaken to be vitiligo. The common medicinal treatment for phytophotodermatitis was ground Elder herb.^[12]

In current practice, the patient's history is essential in making the correct diagnosis of phytophotodermatitis. The clinician must be aware that this entity exists and inquire about contact with fruits or plants. This is particularly true if the patient complains of a painful or burning sensation rather than pruritus (which is commonly associated with allergic contact dermatitis). The patient's hobbies, recreational activities, and/or occupation may give essential clues to the most likely culprits.

Phytophotodermatitis most commonly occurs in the spring and the summer when furocoumarins are at their highest concentration in plants and when UV exposure is greatest for patients. For instance, children playing outdoors may come in contact with meadow grass of the Umbelliferae family.

Agricultural workers may develop phytophotodermatitis when picking parsley (Cymopteris watsonii), parsnips (Pastinaca sativa), celery (Apium graveolens), and/or carrots (Daucus carota). The resulting photocutaneous reaction in this group has been called harvester's dermatitis and is primarily due to exposure to Umbellifers. Another report describes an outbreak of "strimmer rash" in several grounds operatives who had all undertaken grass-cutting duties. The affecting agent was likely giant hogweed, also from the Umbellifers.

Cneoridium dumosum is a plant found along the southwestern coastal United States to which hikers may be exposed, resulting in phytophotodermatitis. Patients are often attracted to this plant by its scented white flower and red berries.

Bartenders and grocers classically develop phytophotodermatitis due to exposure to limes and celery, respectively.^{[13, 14]}

Several reports describe patients creating fig leaf decoctions to use as "tanning lotions" or "suntan promoters." Fig leaves (Ficus carica or Ficus benjamina) are either ground up, boiled, or mixed with oil and then applied on the skin.^{[15, 16]} Patients reported having found these decoction recipes from magazines and/or friends.

One report describes a patient rubbing the juice of medicinal limes (Citrus hystrix) onto the skin as a treatment for insect bites and as an insect repellent, which subsequently resulted in phytophotodermatitis.

Another report describes a patient rubbing the juice of medicinal lime (C hystrix) onto the scalp hair to dye his hair. The juice trickled in between his fingers onto the back of his hands and down the arms to the elbows, where the patient developed phytophotodermatitis.

One case of iatrogenic phytophotodermatitis resulted from ingestion of an herbal remedy prescribed for chronic hand dermatitis.^[17] Plant fragments contained in the herbal mix included extracts from Compositae, a member of the daisy family. No reports describe phytophotodermatitis after contact with members of the Compositae family. However, the action of boiling the plant mix may have possibly released high concentrations of intracellular furocoumarins.

One study assessed the potential of a small amount of psoralen in a normal diet to provoke phototoxicity in volunteers with skin types I and II. The study concluded that threshold erythema and phytophotodermatitis was unaffected by ingestion of this normal dietary amount of fresh parsnips.^[18]

Another study reports on a 30-year-old man who trimmed the stems of a F pumila shrub while exposing his forearms, antecubital fossae, neck, and forehead. Within the following 3 days, the patient noticed eruptions appearing on the exposed areas. Six weeks following, the patient experienced confettilike hypomelanosis over the prior-unprotected areas of the skin. He was treated with clobetasol propionate cream.

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Physical Examination

The primary skin lesion of phytophotodermatitis may range from delayed erythema (24-48 h) to frank blisters. The skin lesions are limited to the areas in contact with furocoumarin and with sunlight exposure. The primary lesion is often not seen by the physician because of the transient nature of the reaction. Rather, the patient presents with late skin changes that become apparent after 72 hours.

Late skin lesions

Bizarre inflammatory patterns and linear streaks of hyperpigmentation are key clues to diagnosing phytophotodermatitis. These patterns often result from brushing against a plant's stems or leaves while outdoors or from the liquid spread of lime juice over the hand or down the forearm. A handprint pattern from lime juice contact is not uncommon. See the images below.

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A 37-year-old white woman presented to the clinic complaining of a rash on the medial part of her right thigh and left arm that was acquired after cle....

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Closer clinical view of bizarre angulated vesicular streaks, which occurred after contact with a plant and ultraviolet light exposure.

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A 26-year-old female airline flight attendant exposed to lime while serving drinks en route to the Caribbean. During the Caribbean layover, she had si....

Furthermore, a buckshot spray over exposed surfaces is commonly seen in association with the use of string trimmers (weed-whackers) when unwanted weeds possessing furocoumarins are cleared from a field or a yard.

Skin distribution

Phytophotodermatitis is most commonly found on skin sites exposed to plants and sunlight; these include such areas as the arms and the legs, but it may occur anywhere.

Skin color

Skin color varies depending on the patient's underlying skin tone and the degree of the reaction. However, as previously stated, the acute phase of phytophotodermatitis manifests as erythema, and the end stage manifests as postinflammatory hyperpigmentation, as shown below.

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The 2-month follow-up picture of a patient with a drip-pattern blister formation on the dorsal forearm demonstrates the potential postinflammatory pig....

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Laboratory Studies

Phytophotodermatitis (PPD) is a clinical diagnosis. All laboratory data obtained are used to support the diagnosis and to exclude other diseases in the differential diagnosis.

Serum psoralen levels may be checked if unknown ingestion of psoralens is suspected.

Porphyrin levels may be obtained to rule out porphyria cutanea tarda.

If the clinical picture does not clearly distinguish between photoallergic and phototoxic dermatitis, performing a photopatch test may be prudent. The photopatch test should include testing for sunscreens because they may be a cause of allergic contact dermatitis associated with sun exposure.

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Procedures

A skin biopsy may be performed to determine the clinical diagnosis if it remains in question and to help distinguish between allergic contact, photoallergic, and photodrug reactions.

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Histologic Findings

Epidermal hyperkeratosis, with or without parakeratosis, is observed. Scattered necrotic keratinocytes (apoptotic cells) are found in the epidermis. Sunburn cells (cells with pyknotic nuclei, increased volume, and pale staining cytoplasm) are also found in the epidermis. Slight spongiosis is observed in the epidermis. Minimal inflammatory cell infiltrate consisting of neutrophils (predominant cell type early on), lymphocytes (less common), and macrophages and melanophages (late) is present. Subepidermal blistering and extravasation of erythrocytes may or may not be present. Pigment incontinence with melanophages is observed in the papillary dermis. The dermis shows some edema and enlargement of vascular endothelial cells.

Both light microscopy and transmission electron microscopy in animal models show keratinocyte necrosis and vacuolization within 24 hours. Within 72 hours, intraepidermal and subepidermal blistering is visible.^{[26, 27]}

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Medical Care

Patient reassurance is essential once the diagnosis is made. Phytophotodermatitis (PPD) is a self-limited problem that resolves with removal of the offending agent. Patients should avoid the offending agent (furocoumarin).

Cool wet compresses may be used for acute lesions. Topical steroids may be used if the eruption is severe and edematous. Indomethacin (50-75 mg PO qd) may be used for adults.

If a severe case evolves or greater than 30% of the body is affected, then it is recommended for the patient to be admitted to a burn unit for local wound care.

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Consultations

Referral to a dermatologist may be useful.

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Activity

Use of UV-A sunscreens may help prevent further phototoxic reactions from occurring when exposed to sunlight.

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Prevention

Regular use of UV-A–blocking sunscreens may help to diminish the cutaneous effects of phytophotodermatitis if contact with plant psoralens occurs.

Patients should avoid the offending agent.

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Medication Summary

The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

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Hydrocortisone valerate 0.2% cream (Westcort)

• Dosing, Interactions, etc.

Clinical Context:  Hydrocortisone valerate 0.2% cream treats inflammatory dermatoses responsive to steroids. It dDecreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing capillary permeability.

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Clobetasol (Temovate)

• Dosing, Interactions, etc.

Clinical Context:  Clobetasol is a class I superpotent topical steroid; it suppresses mitosis and increases the synthesis of proteins that decrease inflammation and cause vasoconstriction.

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Betamethasone topical (Diprolene, Betatrex)

• Dosing, Interactions, etc.

Clinical Context:  Betamethasone topical is for inflammatory dermatoses responsive to steroids. It decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing capillary permeability.

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Class Summary

These agents have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli. Low-to-high potency topical steroids may be applied to affected areas to reduce local inflammation induced by the photoactivated psoralens. They may help to relieve the burning sensation associated with phytophotodermatitis as well as to reduce the associated postinflammatory hyperpigmentation.

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Indomethacin (Indocin)

• Dosing, Interactions, etc.

Clinical Context:  Indomethacin has anti-inflammatory properties resulting from the inhibition of prostaglandin synthesis and/or leukocyte migration into inflamed areas. It is rapidly absorbed; metabolism occurs in the liver by demethylation, deacetylation, and glucuronide conjugation.

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Class Summary

These agents are most commonly used for relief of mild to moderate pain. Indomethacin is an analgesic and NSAID medication that may offer some protection against acute UV-A–induced epidermal apoptosis as well as provide some relief of skin discomfort.

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