What are the differential diagnoses and recommended management plan for a patient with biopsy‑confirmed atopic dermatitis who, after a three‑year hiatus, now presents with recurrent atopic dermatitis, scaly scalp and behind‑ear lesions, central facial dermatitis, yellow‑fluorescing scaly patches on the lower neck under Wood’s lamp, and a hyper‑active edged erythematous plaque under the breast suggestive of psoriasis?

Differential Diagnosis and Management Plan

This patient presents with overlapping inflammatory dermatoses requiring systematic evaluation: the recurrent atopic dermatitis is complicated by probable seborrheic dermatitis (scalp, retroauricular, facial involvement), tinea versicolor (yellow fluorescence on neck), and either tinea corporis or psoriasis (submammary plaque). 1

Differential Diagnoses by Anatomic Site

Confirmed: Atopic Dermatitis (Biopsy-Proven)

• Recurrent disease after 3-year remission
• Typical distribution pattern expected based on patient age 1

Scalp, Retroauricular, and Central Face

Primary consideration: Seborrheic dermatitis

• Classic distribution (scalp, behind ears, central face with greasy scales)
• Commonly coexists with atopic dermatitis 2, 3
• Distinguished from AD by greasier scale, less pruritus, and specific distribution

Lower Neck Lesions (Yellow Fluorescence)

Diagnosis: Tinea versicolor (Pityriasis versicolor)

• Yellow-gold fluorescence under Wood's lamp is pathognomonic
• Caused by Malassezia species
• Presents as scaly patches
• KOH preparation will show "spaghetti and meatballs" pattern

Submammary Plaque

Two primary considerations:

1. Tinea corporis - if truly hyperactive (advancing) edge with central clearing

   • Fungal culture or KOH preparation needed
   • Common in intertriginous areas

2. Psoriasis - if well-demarcated erythematous plaque with silvery scale

   • Can coexist with AD (though uncommon) 2
   • Biopsy if diagnosis unclear

Immediate Diagnostic Workup

Perform these tests at the current visit:

1. KOH preparation from submammary plaque and neck lesions
2. Fungal culture from both sites if KOH equivocal
3. Skin scraping from neck for microscopy (tinea versicolor confirmation)
4. Consider punch biopsy of submammary plaque if KOH negative and psoriasis suspected
5. Bacterial culture if any crusting/weeping suggests secondary infection 4

Management Algorithm

Step 1: Treat Confirmed Atopic Dermatitis

Baseline therapy (restart immediately):

• Emollients: Fragrance-free, applied liberally 2-3 times daily, especially after bathing 1, 5
• Topical corticosteroids:
  • Low-to-medium potency (fluticasone, mometasone) for trunk/extremities
  • Apply once-twice daily until significant improvement 1
  • Proactive therapy: After stabilization, apply twice weekly to previously affected areas for up to 16 weeks to prevent flares 1, 6
• Alternative: Topical calcineurin inhibitors (tacrolimus 0.1% or pimecrolimus 1%) for maintenance 2-3 times weekly 1, 6

If moderate-to-severe or refractory:

• Consider systemic therapy: dupilumab, tralokinumab, JAK inhibitors (baricitinib, upadacitinib, abrocitinib) are strongly recommended 7, 8
• Wet-wrap therapy for 3-7 days (maximum 14 days) for severe flares 1

Step 2: Treat Seborrheic Dermatitis

Scalp:

• Ketoconazole 2% shampoo twice weekly
• Alternative: selenium sulfide or zinc pyrithione shampoo

Face and retroauricular:

• Ketoconazole 2% cream once daily for 2-4 weeks
• Low-potency topical corticosteroid (hydrocortisone 1-2.5%) for initial inflammation control
• Avoid prolonged facial steroid use (maximum 2 weeks) 1

Step 3: Treat Tinea Versicolor (Neck)

First-line:

• Ketoconazole 2% shampoo: apply to affected areas, leave 5-10 minutes, rinse; daily for 1-2 weeks
• Alternative: selenium sulfide 2.5% lotion with same regimen

If extensive:

• Oral fluconazole 400mg single dose, repeat in 1 week
• Or itraconazole 200mg daily for 5-7 days

Step 4: Treat Submammary Lesion

If KOH/culture confirms tinea corporis:

• Topical antifungal (terbinafine 1% or clotrimazole) twice daily for 2-4 weeks
• Extend treatment 1 week beyond clinical clearing

If psoriasis confirmed:

• Medium-potency topical corticosteroid (triamcinolone 0.1%) twice daily
• Consider calcipotriene/betamethasone combination
• If extensive psoriasis develops, systemic therapy may be needed

Step 5: Address Secondary Bacterial Infection (If Present)

If crusting, weeping, or impetiginization:

• Flucloxacillin 500mg four times daily for 7-10 days (first-line for S. aureus) 4
• Erythromycin if penicillin allergy
• Consider dilute bleach baths (0.005%) twice weekly for recurrent infections 9

Ongoing Management Strategy

Follow-up schedule:

• 2 weeks: Assess response to antifungals and topical AD therapy
• 4-6 weeks: Evaluate need for systemic AD therapy if inadequate response
• 3 months: Transition to maintenance regimen

Maintenance plan:

• Continue emollients indefinitely
• Proactive topical anti-inflammatory therapy (TCS or TCI) 2 times weekly to prevent AD flares 6
• Ketoconazole shampoo once weekly for seborrheic dermatitis maintenance
• Monitor for tinea versicolor recurrence (common)

Critical Pitfalls to Avoid

1. Do not assume all lesions are atopic dermatitis - this patient has at least 3-4 distinct conditions requiring different treatments 2, 3

2. Do not use high-potency steroids on face - risk of atrophy, especially with concurrent seborrheic dermatitis 1

3. Do not treat presumed fungal infections without confirmation - obtain KOH/culture before starting therapy

4. Do not overlook secondary bacterial infection - S. aureus colonization is common in AD and requires treatment 4

5. Do not delay systemic therapy if AD is moderate-to-severe - quality of life impact justifies aggressive treatment 7, 10

6. Avoid systemic corticosteroids for AD maintenance - conditional recommendation against due to rebound and adverse effects 7