Diagnosis: Contact dermatitis
The patient’s history and skin exam provided enough information to diagnose contact dermatitis. The pruritus, burning, and pain the patient had experienced were due to continuous application of the lidocaine patch to the area rather than postherpetic neuralgia.
There are 2 types of contact dermatitis: irritant and allergic. Irritant contact dermatitis is an inflammatory reaction caused directly by a substance, while allergic contact dermatitis is a delayed hypersensitivity reaction to specific allergens.1 While data to elucidate the incidence and prevalence of allergic contact dermatitis are unknown, common causes include latex, dyes, oils, resins, and compounds in textiles, rubber, cosmetics, and other products used in daily life.1
Allergic contact dermatitis due to lidocaine is becoming more prevalent with increased use and availability of over-the-counter products.2 A retrospective chart review of 1819 patch-tested patients from the University of British Columbia Contact Dermatitis Clinic showed a significant proportion of patients (2.4%) were found to have an allergic contact dermatitis to local anesthetics—most commonly benzocaine (45%), followed by lidocaine (32%).3 Therefore, it is important to consider contact dermatitis in patients using topical anesthetics for pain relief.
The differential varies by area affected
The differential diagnosis for contact dermatitis varies by area affected and the distribution of rash. Atopic dermatitis, lichen planus, and psoriasis are a few dermatologic conditions to consider in the differential diagnosis. They can look similar to contact dermatitis, but the patient’s history can help to discern the most likely diagnosis.1
Atopic dermatitis is a complex dysfunction of the skin barrier and immune factors that often begins in childhood and persists in some patients throughout their lifetime. Atopic dermatitis is associated with other forms of atopy including asthma, allergic rhinitis, and food and contact allergies. Atopic dermatitis in the absence of contact allergies may manifest with chronic, diffuse, scaly patches with poorly defined borders. The patches appear in a symmetrical distribution and favor the flexural surfaces, such as the antecubital fossa, wrists, and neck.
Continue to: Lichen planus