Venous Eczema Contact Allergy — SCE Dermatology MCQ

Correct answer: A — Approximately 50-80% have at least one positive patch test to a medicament or wound care product

The correct answer is A, approximately 50 to 80 percent have at least one positive patch test to a medicament or wound care product. Chronic venous ulceration and venous eczema cause a persistently disrupted, inflamed epidermal barrier, and patients are typically exposed for months or years to multiple topical agents (antibiotics, antiseptics, emollient excipients, bandage components), which together markedly increase sensitisation risk compared with the general population. This is why venous eczema that worsens on treatment, as in this man reacting to topical neomycin, should prompt suspicion of allergic contact dermatitis and referral for patch testing rather than escalating or switching topical antimicrobials. Leg ulcer clinic studies consistently report positive patch test rates in this range, with fragrances, antimicrobials (including neomycin and framycetin), lanolin, and rubber or adhesive components being leading culprits. UK dermatology guidance recommends patch testing patients with chronic venous leg ulcers or eczema failing to improve, or worsening, on treatment. Why the other options are wrong: B. 10%: Far too low; studies of leg ulcer populations consistently show sensitisation rates several times higher than this. D. Less than 1%: This reflects sensitisation risk with standard topical agents in intact skin, not the chronically damaged, repeatedly treated skin of venous disease. E. 5%: Still substantially underestimates true prevalence; contact allergy is common rather than rare in this group because of prolonged allergen exposure through impaired skin barrier. C. 100%: Overstates the finding; sensitisation is very common but not universal, and a meaningful proportion of patients patch test negative to all allergens tested. Key point: Venous eczema or ulceration that fails to improve, or worsens, on topical treatment should prompt patch testing, since 50 to 80 percent of these patients develop contact allergy to a medicament or wound care product.

Reference: Patient.info (Doctor) / UK primary care guidance, Varicose Eczema (Venous Eczema) - Symptoms and Treatment: notes that contact allergic dermatitis to paste bandages and medicaments applied to leg ulcers is common and warrants dermatology referral for patch testing; corroborated by UK leg ulcer clinic patch test studies (e.g. Cameron J et al, Lanarkshire series, Contact Dermatitis) reporting positive patch tests in 68-80% of venous leg ulcer patients. https://patient.info/doctor/varicose-eczema-pro