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.
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.
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. [30, 31]
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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 clearing some weeds in her yard. A phototoxic combination of sunlight and a psoralen-containing plant produced this bizarre linear vesicular eruption.
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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 significant sun exposure. The combination of lime juice and sun exposure led to a drip-pattern blister formation on the dorsal forearm consistent with phytophotodermatitis. This picture clearly delineates the potential severity of phytophotodermatitis with extensive blister formation.
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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 pigmentation changes and scarring that may occur with severe blistering of phytophotodermatitis.
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Close-up view of vesicular linear streaks with morphology suggestive of scattered foci of epidermal necrosis.
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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.
Tables
Family |
Genus |
Species |
Common Names |
Main Compounds |
Umbelliferae |
Amni |
majus |
Queen Anne's lace, Bishop's weed |
8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP), imperatorin |
Heracleum |
sphondylium |
Cow parsnip |
8-MOP, 5-MOP, imperatorin, phellopterin |
|
Heracleum |
mantegazzianum |
Giant hogweed, [11] Cartwheel flower |
8-MOP, 5-MOP, imperatorin, phellopterin |
|
Pastinaca |
sativa |
Parsnip |
8-MOP, 5-MOP, imperatorin, isopimpinellin |
|
Apium |
graveolens |
Celery |
Psoralens, 8-MOP, 5-MOP |
|
Rutaceae |
Citrus |
bergamia |
Bergamot lime |
5-MOP |
Citrus |
maxima |
Zabon [12] |
5-MOP |
|
Dictamnus |
albus |
Gas plant, “Burning bush of Moses” |
8-MOP, 5-MOP |
|
Moracea |
Ficus |
carica |
Psoralens, 5-MOP |
|
Leguminosae |
Psoralea |
corylifolia |
Bavchi, Scurf pea |
Psoralens |
