Differential Diagnosis of Eczematous Lesion at Angle of Mouth
The primary differential diagnoses for an eczematous lesion at the angle of the mouth include allergic contact dermatitis, irritant contact dermatitis, atopic dermatitis, seborrheic dermatitis, and angular cheilitis (perleche). 1
Primary Considerations
Allergic Contact Dermatitis
- Most common cause of perioral eczematous lesions, accounting for 32-44% of perioral dermatitis cases 2
- Occurs only in sensitized individuals with predisposition to specific allergens 1
- Common culprits include:
- Presents as maculopapular, often eczematous eruption with erythema, edema, scaling, and pruritus 1
- Patch testing is essential for diagnosis when contact allergy is suspected, particularly with persistent or recalcitrant lesions 1
Irritant Contact Dermatitis
- Accounts for 8-9% of perioral dermatitis cases 2
- Results from direct chemical damage to skin from acids, alkalis, or chronic exposure to saliva, foods, or detergents 1, 3
- All individuals are susceptible in a dose-dependent manner, unlike allergic contact dermatitis 1
- Patients report stinging and burning more than pruritus (unlike atopic dermatitis) 3
- Lesions are typically well-demarcated 3
- Diagnosed by exclusion after ruling out type I and IV hypersensitivity 3
Atopic Dermatitis
- Accounts for 14-25% of perioral dermatitis cases 2
- Essential features must include: pruritus, typical eczematous morphology with age-specific patterns, and chronic/relapsing history 1
- Perioral changes are listed as "other regional findings" in atopic dermatitis diagnostic criteria 1
- Usually involves multiple body areas, not isolated to perioral region 1
- Spares groin and axillary regions (unlike seborrheic dermatitis) 1
- Chronic pruritus typically starting in childhood with involvement of flexural areas 1
Seborrheic Dermatitis
- Common condition affecting central face and other sebaceous areas 1, 4
- Presents with greasy yellowish scaling, itching, and secondary inflammation from Malassezia yeast 1, 4
- More pronounced in patients with Down syndrome, HIV infection, and Parkinson's disease 1, 4
- Unlike atopic dermatitis, affects groin and axillary regions and tends to be less pruritic 1
- Treatment includes topical antifungal medications and anti-inflammatory agents 1, 4
Clinical Approach to Diagnosis
Key Distinguishing Features
- Distribution pattern: Isolated perioral involvement suggests contact dermatitis; widespread involvement suggests atopic dermatitis 1, 2
- Symptom quality: Burning/stinging favors irritant contact dermatitis; intense pruritus favors atopic dermatitis or allergic contact dermatitis 1, 3
- Age of onset: Childhood onset with chronic course suggests atopic dermatitis 1
- Lesion characteristics: Well-demarcated lesions suggest irritant contact dermatitis; greasy yellowish scale suggests seborrheic dermatitis 1, 3
Diagnostic Testing
- Patch testing should be performed when allergic contact dermatitis is suspected, particularly with unusual distribution, later onset, new worsening, or persistent/recalcitrant disease 1
- Patch testing has sensitivity of 60-80% and requires assessment at 48 hours and again up to 7 days for delayed reactions 1
- Most common allergens to test: nickel, neomycin, fragrances, formaldehyde, preservatives, lanolin, rubber chemicals 1
- Consider KOH preparation if fungal infection suspected 1
Common Pitfalls
- Failing to consider contact dermatitis in patients with known atopic dermatitis, as allergic contact dermatitis occurs in 6-60% of atopic dermatitis patients 1
- Overlooking occupational or hobby-related exposures to irritants or allergens 1
- Not recognizing that multiple conditions can coexist: irritant contact dermatitis, allergic contact dermatitis, and atopic dermatitis may occur simultaneously 3, 5
- Assuming isolated perioral involvement is atopic dermatitis without considering contact dermatitis, which is more common in this location 2
- Missing neomycin allergy in patients using topical antibiotics, as 5-15% of patients with chronic dermatitis are sensitized 1