Page 141 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 4-56 Rashes

PHYTOPHOTODERMATITIS Hyperpigmented macules with or without an inflammatory
stage. This is caused by the phototoxic effect of psoralens
found in various foods such as lime and parsnip.
Phytophotodermatitis is a specific form of phototoxic
or photoirritant contact dermatitis. The offending
agent is a plant species from one of a few specific fami-
lies. This form of dermatitis has an insidious onset and
is typically preceded by little to no inflammation. This
can make the diagnosis difficult for the clinician. Rec-
ognition of the key clinical features and the species of
plant involved help make the diagnosis.
Clinical Findings: Phytophotodermatitis is caused
by certain species of plants that come into contact with
the skin. Lone contact with skin is not enough to cause
the inflammatory reaction and subsequent postinflam-
matory hyperpigmentation: After exposure to the plant
material, there is a time frame during which the exposed
area must be introduced to ultraviolet radiation. It is
the plant oils and resins in combination with the correct
ultraviolet source that leads to the characteristic rash.
The most typical clinical scenario encountered is one
in which the patient comes into contact with a plant
that contains a psoralen compound. One of the most
frequently reported causes is the juice of a lime (Citrus
aurantifolia). This plant is categorized within the Ruta-
ceae family. The Rutaceae family is the most wide-
spread family of plants that have been described to
cause these types of reactions, with the lime being by
far the most common offender.
Patients often describe the use of a lime in a mixed
drink while vacationing on the beach. The lime juice
contacts the skin, and when the skin is exposed to a
specific threshold of ultraviolet light, the reaction
develops. Most often, patients do not complain of any
acute symptoms. If the reaction is severe, burning
occurs acutely and the diagnosis is relatively straight- Lime and parsnip
forward. However, most reactions are subtle and do not
appear for a few days to weeks. Patients typically return
home from vacation and notice a subtle hyperpigmen-
tation around the mouth or scattered on the body
where they have splashed or consciously applied the
juice from a lime during sun bathing. The hyperpig-
mentation may last for months to years. On rare occa- The lime is the most frequent cause of this
sions, a severe acute reaction occurs with red plaque and reaction. Bartenders and beach vacationers
vesicle formation. who drink beverages with a slice of lime
The many families of plants capable of initiating are commonly afflicted.
this type of reaction all contain the chemical psoralen.
Psoralen is a potent photosensitizer that is used
clinically. Once purified, it can be given orally in
the form of psoralen + ultraviolet A light (PUVA) Families of Plants Known to Cause Phytophotodermatitis and Some Representative Species
therapy or painted on for topical PUVA therapy. It is
especially helpful for treating refractory hand and foot Umbelliferae Rutaceae
dermatoses. Dill–Anethum graveolens Rue–Cneoridium dumosum
The areas of involvement are typically asymptomatic Parsley–Petroselinum crispum Lemon–Citrus limon
and do not show any overt inflammatory features. They Parsnip–Heracleum sphondylium Lime–Citrus aurantifolia
appear as hyperpigmented, irregularly shaped macules Giant hogweed–Heracleum mantegazzianium Orange–Citrus sinensis
on the skin. These spontaneously remit over a few Moraceae Leguminosae
months. Many plants are capable of producing the Fig–Ficus carica Scurf pea–Psoralea corylifolia
reaction.
Pathogenesis: Almost all of the plants responsible for
phytophotodermatitis come from four specific families:
Umbelliferae, Rutaceae, Moraceae, and Leguminosae.
These plants all contain potent photosensitizers in to interrupt DNA synthesis. The psoralen and ultravio- Treatment: Acute areas of involvement can be
varying concentrations. The chemicals responsible for let light also can cause hyperpigmentation (tanning). treated with topical corticosteroid creams. The main
photosensitization are the furocoumarins; more specifi- Histology: The pathological features are dependent issue in management is dealing with the prolonged
cally, the psoralens are by far the most important of the on the timing of the biopsy. An acutely inflamed lesion postinflammatory hyperpigmentation. No therapy has
photosensitizer chemicals. On contact, the psoralen shows a superficial perivascular lymphocytic infiltrate been shown to be helpful, but almost all reactions
penetrates the skin. Subsequent exposure to ultraviolet and dermal edema with apoptotic keratinocytes within resolve slowly over time. Care should be taken not to
A light in the spectrum of 320 to 400 nm causes pyrimi- the epidermis. Late lesions show melanophages within perform a treatment that might lead to a worse cos-
dine dimers to form within the DNA strands, which act the dermis. metic outcome.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 127