History
You are asked to review a 72-year-old retired hairdresser, who attends the leg-ulcer clinic because of a 4-week history of progressive worsening pruritus of her right lower leg. Prior to this she had a venous ulcer over the medial malleolus of her right leg, which has gradually healed over a 4-month period with the diligent application of three-layer compression bandaging by her local nursing team. Her treatment regime includes a wash with chlorhexidine containing emollient lotion, application of paraffin emollient to the entire lower leg, followed by betamethasone–neomycin ointment applied directly to areas of stasis eczema and easy-release gauze over the ulcerated area. The three-layer bandages are changed twice weekly. Skin swabs have been taken over the past couple of weeks because of the worsening skin rash. She is otherwise well. Her only oral medication is bendroflumethiazide 2.5 mg daily for hypertension.
Examination
Physical examination reveals a large but localized area of intense erythema and skin swelling confined to the anterior, posterior and medial aspect of her right lower leg (Fig. 8.1). There is marked exudate with suggestion of surface vesiculation. No involve-ment of her skin above her knee or foot is apparent. Although her skin is sore and itchy there is no swelling or tenderness of her calf. She has no palpable lymphadenopathy. The rest of her examination including peripheral arterial examination was normal.
Questions
• What is likely to have caused the acute deterioration?
• How would you investigate this patient?
• What advice will you give the patient?
Medicine
With acute erythema and swelling of the leg one of the most important differential diagnoses to consider would be a deep venous thrombosis (DVT). However DVTs are not associated with the significant degree of epidermal change seen in this case, particularly in the absence of any other suggestive features (such as swelling or intramuscular tender-ness). The negative skin swab does not rule out cellulitis; the morphology and distribution of the eruption would, however, be atypical and the absence of raised white cell count or inflammatory markers effectively rules it out. The clinical features in this case are highly suggestive of dermatitis (stasis, irritant or allergic contact dermatitis). The extensive involvement and vesiculation would be unu-sual for stasis dermatitis, which is usually confined to the ‘gaiter’ area, particularly above the medial malleolus. The most appropriate investigation would be patch testing. Individuals with stasis derma-titis and stasis ulcers are at high risk for developing allergic contact dermatitis to topical medications applied to inflamed or ulcerated skin. Patients may also develop allergies to constituents of the bandages and dressings applied. The chronicity of this condition and the frequent occlusion of applied medications in these patients contribute to the high risk of allergic contact dermatitis to preservatives in medications and/or to the active ingredients in topical medications. Although neomycin penetrates intact skin poorly, it is an important cause of allergic contact dermatitis when applied to patients with venous stasis/ulceration. It is used surprisingly frequently despite the lack of documentation of its efficacy in the treat-ment of stasis ulcers. (Its poor penetration may explain the fact that a positive patch test reaction to neomycin may be delayed for four days or later following initial application.) Individuals may develop widespread dermatitis from topical medications applied to leg ulcers or from cross-reacting systemic medications administered intravenously. Neomycin is also commonly found in combination preparations with other antibacterials and cortico-steroids. These prescription and non-prescription preparations are used to treat a variety of skin, eye and external ear disorders that have become infected and inflamed. Neomycin is also present as a preservative in some vaccine preparations. It should be assumed that indi-viduals allergic to neomycin are allergic to chemically related aminoglycoside antibiotics (e.g. gentamicin, tobramycin) and these agents should be avoided (topically or systemically).
KEY POINTS
• The possibility of an external cause of dermatitis must always be considered if the dermatitis is linear or sharply defined.
• Medications are important causes of allergic contact dermatitis. Individuals with stasis dermatitis are at high risk for developing allergic contact dermatitis.
• Individuals may develop allergy to preservatives in medications and/or to the active ingredients in topical medications, especially neomycin and topical corticosteroids.
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