History
A 33-year-old woman presents with a sudden-onset blistering rash on her legs. On closer questioning she reports no recent history of travel or contact with animals. She recently moved into new accommodation and has been clearing an overgrown garden over the past few days. She has been clearing weeds by hand but wore garden gloves and bor-rowed a strimmer from a friend to cut through long grass. She felt an intense itching on her lower legs and then noticed blisters in a streaking pattern. She has no previous history of skin disease or atopy and is otherwise well.
Examination
Linear vesicular lesions with associated erythema and excoriations are seen on her legs (Fig. 16.1). There are tense bullae filled with clear serous fluid. Full skin examination is otherwise unremarkable including mucosal membranes.
Questions
• What is the most likely diagnosis?
• What is the underlying cause?
• How would you manage this patient?
Medicine
This patient is suffering from phytophotodermatitis, which is a phototoxic skin eruption. This acute inflammatory condition is triggered by the combination of skin contact with photosensitizing chemicals in plants plus sunlight. Patients usually report burning or itching of their skin prior to the onset of blistering. The characteristic skin patterns result from the plant brushing against bare skin whilst outdoors. The diagnosis is made on the history of plant exposure and from the clinical appearance of linear blisters, usually on exposed skin. The morphology of the rash looks very exog-enous (linear or bizarre-shaped streaks) with erythema, vesicles, bullae and oedema which classically resolve leaving post-inflammatory hyperpigmentation. Although gardeners are most commonly affected, exposure to lime-juice in the preparation of drinks outdoors is another typical presentation. Phytophotodermatitis usually occurs in the spring and summer months. The main pho-tosensitizing substances found in plants are called furocoumarins, which consist of psoralens, 5,8-methoxypsoralens, angelicin, bergaptol and xanthotal. The most common plant family implicated is the Umbelliferae, which includes giant hogweed, celery, wild parsnip and parsley. Other plant families that cause phytophotodermatitis are Rutaceae (lime) and Leguminosae (beans). The characteristic rash may appear within minutes to hours after exposure to the plant and utraviolet light, but more usually erupts 24 hours (peak 48–72 hours) after exposure. Phytophotodermatitis is a self-limiting skin eruption; however, it is intensely itchy and blistering. Super-potent topical steroid should be applied twice daily to the affected area for 1–2 weeks. Large tense bullae should be deflated with a sterile needle. Advice should be given to patients concerning the use of personal protective clothing if continuing with similar outdoor work.
KEY POINTS
• Phytophotodermatitis occurs due to the combination of skin contact with photosensitizing chemicals in plants plus sunlight.
• The main photosensitizing substances found in plants are called furocoumarins.
• The acute eruption should respond to potent topical steroids.
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