What is the initial management for a patient presenting with symptoms suggestive of contact dermatitis?

Differential Diagnosis of Contact Dermatitis

The key differential diagnoses for contact dermatitis include atopic dermatitis, seborrheic dermatitis, nummular eczema, stasis dermatitis, psoriasis, and tinea infections—all of which can present with similar eczematous lesions but require distinct clinical history, distribution patterns, and patch testing to differentiate. 1

Primary Differential: Atopic Dermatitis vs. Contact Dermatitis

Distinguishing between atopic dermatitis (AD) and allergic contact dermatitis (ACD) is particularly challenging because both manifest as eczematous lesions and are often clinically indistinguishable. 1

• ACD occurs in 6-60% of patients with AD, making it both an alternative diagnosis and a concomitant condition that must be actively considered. 1

• Pattern recognition is unreliable—the British Association of Dermatologists emphasizes that morphology and distribution alone, especially on hands and face, cannot reliably distinguish between irritant, allergic, or endogenous (atopic) dermatitis. 1

• Key clinical clues favoring ACD over AD include: 1

  • Disease aggravated by specific topical medications or emollients
  • Marked facial and/or eyelid involvement
  • Increased severity at neck flexures
  • Vesicular lesions on dorsal hands and fingertips
  • Unusual distribution (e.g., sides of feet)
  • Later onset or new significant worsening
  • Absence of family history of atopy
  • Persistent/recalcitrant disease not responding to standard AD therapies

Irritant Contact Dermatitis vs. Allergic Contact Dermatitis

These two forms of contact dermatitis require differentiation, though clinical appearance alone is insufficient. 1, 2

• Irritant contact dermatitis results from non-immune-mediated skin damage from single overwhelming exposure or repetitive exposure to weaker irritants (detergents, solvents, soaps). 3, 2

• Allergic contact dermatitis is a type IV delayed hypersensitivity reaction requiring prior sensitization, with symptoms appearing after reexposure to the allergen. 1, 2

• Patch testing is the definitive method to distinguish allergic from irritant contact dermatitis, with sensitivity ranging from 60-80%. 1

Other Important Differentials

Seborrheic Dermatitis

• Typically involves scalp, nasolabial folds, eyebrows, and central chest with greasy yellow scales rather than the vesiculation seen in acute contact dermatitis. 4

Nummular Eczema

• Presents as coin-shaped plaques, typically on extremities, without clear relationship to contactants. 4

Stasis Dermatitis

• Occurs on lower legs in setting of venous insufficiency, with associated edema, hemosiderin deposition, and varicosities. 5, 4

Psoriasis

• Distinguished by well-demarcated plaques with silvery scale, typically on extensor surfaces, and nail changes. 4

Tinea Infections

• Can mimic contact dermatitis but typically show peripheral scale with central clearing; KOH preparation or fungal culture confirms diagnosis. 4

Diagnostic Approach to Differentiation

A detailed history is essential and should specifically address: 1, 3

• Initial location of symptoms and spread pattern
• Temporal relationship to specific products, activities, or occupational exposures
• Recreational exposures and hobbies
• Personal care products used on affected areas
• Improvement with time away from work or specific environments

Patch testing should be performed when: 1, 3

• History or physical exam suggests ACD
• Disease is aggravated by topical treatments
• Unusual or atypical distribution for AD
• Persistent/recalcitrant disease despite appropriate therapy
• Later onset or new significant worsening

Standard patch testing involves: 1

• Application of baseline series (captures ~80% of allergens) to unaffected skin, typically the back
• 48-hour occlusion period
• Readings at patch removal and again at 7 days to capture delayed reactions (~10% additional positive reactions)
• Supplemental series for specific exposures (fragrances, rubber chemicals, etc.)

Critical Diagnostic Pitfalls

Common allergens that cause irritant reactions and are frequently misinterpreted include: 1

• Metal salts (nickel, cobalt, potassium dichromate)
• Fragrances
• Carba mix

A subset of patients develop ACD to topical corticosteroids themselves, creating a diagnostic dilemma where treatment appears to fail. 1, 5

Positive patch tests only indicate contact sensitization—clinical relevance must be demonstrated through correlation with active dermatitis and sometimes confirmed by repeat open application testing. 1

Avoidance of the suspected allergen with resolution of dermatitis confirms the diagnosis of ACD. 1

Special Consideration: Photoallergic Contact Dermatitis

• When photoallergic contact dermatitis is suspected, photopatch testing with duplicate allergen application and UVA irradiation (5 J/cm²) of one side should be performed. 1

• True photoallergy incidence is low (<5% of suspected cases). 1