What is the treatment approach for a 1 year and 8 months old patient with diffuse hives diagnosed with erythema multiforme?

Treatment of Diffuse Hives with Erythema Multiforme in a 20-Month-Old Child

Critical Diagnostic Clarification First

You must first confirm this is truly erythema multiforme (EM) and not urticaria or Stevens-Johnson syndrome (SJS), as these require completely different management approaches. 1, 2

• EM lesions are fixed for minimum 7 days, whereas urticarial lesions resolve within 24 hours 2
• EM presents with target/iris lesions on acral surfaces (hands, feet, extensor surfaces) progressing proximally, not diffuse hives 1, 3
• EM patients remain constitutionally well without systemic illness, fever, or widespread blistering 1
• SJS presents with widespread erythematous or purpuric macules with blisters and mucosal involvement, requires immediate ICU referral 1
• EM does not progress to SJS/TEN - these are separate disease entities 1

Immediate Treatment Approach

For Confirmed EM Minor (Skin Only)

Supportive care with topical corticosteroids and oral antihistamines is the primary treatment for pediatric EM. 2, 4, 5

Symptomatic management:

• Topical high-potency corticosteroids applied to target lesions twice daily 5
• Oral antihistamines for pruritus: diphenhydramine 1.25 mg/kg/dose every 6 hours as needed (maximum 50 mg/dose) 6
• Supportive care only was the most common treatment approach in 31.1% of pediatric EM cases 4

For EM Major (Mucosal Involvement)

If oral mucosa is involved, add:

• Antiseptic or anesthetic oral solutions for mucosal lesions 5
• Adequate hydration - monitor fluid intake closely 3, 2
• Consider hospitalization if oral intake is compromised for IV fluids and electrolyte repletion 2

Identify and Treat the Underlying Trigger

The most critical step is identifying and treating the causative agent, as EM will not resolve until the trigger is addressed. 2, 5

Most Common Triggers in This Age Group:

Infectious causes (most common in children):

• Herpes simplex virus (HSV) - 17.9% of pediatric cases 4
• Mycoplasma pneumoniae - 15.7% of pediatric cases, especially if respiratory symptoms present 4
• Recent vaccination - particularly important in infants/toddlers (3.2% of cases, 47% of infantile EM) 4

If HSV-triggered:

• No acute antiviral treatment needed for first episode of EM minor 2, 5
• Antivirals only indicated for recurrent HSV-associated EM (see below) 2, 5

If Mycoplasma pneumoniae suspected (cough, fever, respiratory symptoms):

• Macrolide antibiotics: azithromycin 10 mg/kg on day 1, then 5 mg/kg daily for 4 days 4
• Macrolides were used in 7.7% of pediatric EM cases 4

If medication-triggered:

• Immediately discontinue the suspected drug 2, 5
• 24.1% of pediatric EM cases were drug-related 4

Systemic Corticosteroids: Use Sparingly

Systemic corticosteroids are NOT first-line for pediatric EM and should be reserved for severe mucosal involvement only. 4, 5

• Used in only 19.8% of pediatric EM cases 4
• Consider oral prednisone 1-2 mg/kg/day for 5-7 days only if extensive mucosal involvement prevents oral intake 5
• Not indicated for EM minor with skin lesions only 2, 5

Expected Course and Follow-Up

EM is self-limited and resolves within 2-4 weeks with supportive care. 3, 2

• Long-term sequelae are rare (1.3%) in pediatric EM 4
• Recurrence occurs in 14.3% of pediatric cases, most commonly HSV-triggered 4
• Infants are less prone to develop EM major than older children 4

Management of Recurrent EM (If This Becomes a Pattern)

If EM recurs (≥6 episodes per year), prophylactic antiviral therapy is indicated if HSV-associated. 2, 5

• Acyclovir prophylaxis: 20 mg/kg/dose twice daily (maximum 400 mg/dose) continuously for 6-12 months 5, 7
• 61% of recurrent pediatric EM is HSV-triggered 4
• If resistant to acyclovir, switch to valacyclovir or famciclovir 7
• If non-responsive to antivirals, consider dapsone or other immunosuppressive agents (specialist consultation required) 7

Critical Pitfalls to Avoid

Do not confuse EM with urticaria - if lesions are migratory and resolve within 24 hours, this is urticaria requiring different treatment (antihistamines only) 2

Do not miss SJS/TEN - if child appears systemically ill, has fever, widespread blistering, or mucosal sloughing, this requires immediate hospital admission 1

Do not prescribe prophylactic antivirals for first episode - only indicated for recurrent HSV-associated EM 2, 5

Do not use topical acyclovir for prophylaxis - it does not prevent recurrent EM episodes 7