What is the most likely diagnosis and appropriate initial management for a 17‑year‑old male with a 3‑day history of pruritic, dry, red‑brown scaly papules localized to the flexor surfaces of both arms and axillae, without known allergen exposure, who had slight improvement with cetirizine?

Atopic Dermatitis (Eczema)

The most likely diagnosis is atopic dermatitis, and you should immediately initiate a regimen of liberal emollient application (at least twice daily to the entire body) combined with a low-to-mid potency topical corticosteroid applied to affected flexural areas twice daily. 1

Diagnostic Confirmation

This 17-year-old male meets the clinical diagnostic criteria for atopic dermatitis based on:

• Pruritic lesions with characteristic flexural distribution (both arms and axillae), which is the hallmark pattern for adolescents and adults with atopic dermatitis 1
• Chronic/relapsing course (3 days represents an acute flare, but the flexural distribution suggests underlying chronic disease) 1
• Dry, scaly papules consistent with eczematous changes 1, 2

The Taiwan Academy of Pediatric Allergy, Asthma and Immunology diagnostic criteria require pruritus with age-specific distribution (flexural in adolescence), eczematous lesions, and chronic/relapsing course—all present here. 1 No laboratory testing is needed; this is a clinical diagnosis. 1, 3

Immediate Management Plan

First-Line Topical Therapy

• Apply fragrance-free emollients liberally at least twice daily to the entire body, not just affected areas, preferably immediately after a 10-15 minute lukewarm bath or shower 1
• Prescribe a mid-potency topical corticosteroid (e.g., triamcinolone acetonide 0.1% cream) to be applied twice daily to the flexural arm lesions and axillae 1, 4
• Emollients have both short- and long-term steroid-sparing effects and are integral to management regardless of severity 1

Antihistamine Role—Limited Benefit

Cetirizine should NOT be relied upon as primary treatment for atopic dermatitis. 1 While the patient experienced "slight relief" with cetirizine, the evidence is clear:

• Non-sedating antihistamines like cetirizine are ineffectual for AD disease control 1
• The ETAC trial showed cetirizine provided no statistically significant improvement in overall AD control over 18 months 1, 5
• Cetirizine may have a modest steroid-sparing effect in severe cases (SCORAD ≥25), but this is not a substitute for proper topical therapy 5
• Short-term sedating antihistamines may help with sleep disruption from itch, but should never replace topical anti-inflammatory treatment 1

You may continue cetirizine 10mg daily for symptomatic pruritus relief, but emphasize to the patient that this addresses symptoms only, not the underlying inflammation. 1

Critical Next Steps

Patient Education (Essential)

• Demonstrate proper application technique for both emollients and topical corticosteroids during the visit 3
• Provide written instructions on frequency and quantity of application 3
• Explain that emollients should be applied generously and frequently, not sparingly 1, 3
• Address any corticosteroid phobia—appropriate use of mid-potency steroids on the body is safe 3

Identify and Eliminate Triggers

• Ask specifically about: excessive sweating, recent changes in soaps/detergents, new clothing materials, stress, and environmental allergen exposure 1
• Recommend cool environmental temperature, smooth cotton clothing, and avoidance of irritating fabrics 1
• Use gentle, fragrance-free cleansers as soap substitutes 3

Monitor for Complications

Watch for signs of secondary infection, which is common in AD:

• Bacterial superinfection (impetiginization): increased crusting, weeping, honey-colored exudate, or worsening despite treatment 3, 6
• If suspected, obtain bacterial swabs and consider empiric flucloxacillin or cephalexin 3, 6
• Eczema herpeticum (rare but serious): multiple uniform "punched-out" erosions or vesiculopustular lesions—this requires immediate systemic acyclovir 3

Follow-Up and Escalation

• Reassess in 1-2 weeks 3, 6
• If no improvement with optimized topical therapy, consider:
  • Topical calcineurin inhibitors (tacrolimus, pimecrolimus) as steroid-sparing agents 1
  • Dermatology referral for consideration of phototherapy or systemic immunomodulators if refractory 1

Common Pitfalls to Avoid

• Do not rely on antihistamines as primary AD treatment—they do not control the underlying inflammatory process 1
• Do not underdose emollients—patients often apply too little; emphasize liberal, frequent application 1, 3
• Do not miss secondary infection—deterioration in previously stable or improving eczema suggests bacterial or viral superinfection 3, 6
• Do not dismiss the axillary involvement—while AD typically spares the axillae in infancy (unlike seborrheic dermatitis), flexural involvement including axillae is characteristic in adolescents 1