What is the diagnosis and first‑line treatment for an adult male who developed penile contact dermatitis with redness, itching, swelling, and rash after handling peony plants?

Penile Contact Dermatitis from Peony Plant Exposure

The diagnosis is allergic or irritant contact dermatitis of the penis, and first-line treatment is mid- to high-potency topical corticosteroids such as hydrocortisone applied 3-4 times daily to the affected area, with avoidance of further peony plant contact. 1, 2

Diagnosis

Contact dermatitis presents with erythematous, pruritic skin lesions with visible borders after exposure to a foreign substance 2. In this case:

• Clinical presentation includes: redness, itching, swelling, and rash localized to the penis following direct handling of peony plants 2
• Two forms exist: irritant contact dermatitis (non-immune mediated direct irritation) and allergic contact dermatitis (delayed hypersensitivity reaction requiring prior sensitization) 2
• Diagnostic confirmation: The first step is determining whether symptoms resolve with avoidance of the causative substance (peony plants in this case) 2

Key Diagnostic Features

• Lesions have visible borders corresponding to contact areas 2
• Acute cases may show dramatic erythema, vesicles, and bullae 2
• Symptoms include itching and discomfort 2
• The genital area is particularly susceptible to contact dermatitis from various substances including plant materials 3, 4

First-Line Treatment

For localized penile contact dermatitis:

• Apply mid- to high-potency topical corticosteroids such as triamcinolone 0.1% or clobetasol 0.05% to affected areas 2
• FDA-approved hydrocortisone (topical) can be applied to the affected genital area not more than 3-4 times daily for adults 1
• Before application: Clean the affected area with mild soap and warm water, rinse thoroughly, and gently dry by patting or blotting 1

When Systemic Treatment Is Required

If contact dermatitis involves extensive skin area (>20% body surface):

• Systemic corticosteroid therapy is required and provides relief within 12-24 hours 2
• For severe cases, oral prednisone should be tapered over 2-3 weeks to prevent rebound dermatitis 2
• Rapid discontinuation of steroids can cause symptom recurrence 2

Critical Management Steps

Immediate Actions

• Complete avoidance of further peony plant contact 2
• Wash hands thoroughly after any plant handling to prevent inadvertent transfer to genital area 2
• Remove contaminated clothing that may have contacted the plants 2

Common Pitfalls to Avoid

• Do not use topical corticosteroids for more than 3-4 times daily as per FDA labeling 1
• Avoid excessive hygiene measures which can cause additional irritation ("over-treatment balanitis") 5
• Do not rapidly discontinue systemic steroids if used, as this causes rebound dermatitis 2

When to Perform Additional Testing

Patch testing should be performed if:

• Treatment fails despite appropriate therapy 2
• The specific allergen remains unknown 2
• The diagnosis is uncertain 2

Biopsy is indicated when:

• Lesions are pigmented, indurated, fixed, or ulcerated 6
• Disease fails to respond to adequate treatment 6
• There is diagnostic uncertainty or atypical features 6
• Neoplastic change is suspected (persistent hyperkeratosis, erosion, erythema, or new warty/papular lesions) 6

Differential Diagnoses to Exclude

The differential diagnosis of penile dermatoses includes 3, 4, 5:

• Infectious causes: bacterial, fungal (Candida), viral (herpes, HPV), or parasitic infections 3, 5
• Inflammatory conditions: psoriasis, lichen planus, lichen sclerosus 6, 3, 5
• Neoplastic lesions: squamous cell carcinoma in situ, Bowen's disease, erythroplasia of Queyrat 6, 3
• Fixed drug reactions 4