How should I treat a patient with a skin biopsy showing surface erosion, perifollicular and periadnexal inflammatory infiltrate, and mixed chronic inflammation, likely due to an insect bite?

Interpretation of Skin Biopsy Results from a Questionable Insect Bite

The skin biopsy findings indicate a hypersensitivity reaction to an insect bite that should be treated with a medium to high-potency topical corticosteroid applied twice daily for 2-4 weeks.

Pathology Interpretation

The biopsy shows classic features of an arthropod bite reaction:

• Surface erosion with fibrin and scale crust
• Brisk perifollicular and periadnexal inflammatory infiltrate
• Mixed chronic inflammation
• Presence of eosinophils and neutrophils

These findings are consistent with a hypersensitivity reaction to an insect bite rather than other dermatological conditions such as:

• Lichen sclerosus (would show epidermal atrophy and homogenization of dermal collagen)
• Bullous dermatoses (would show more extensive blistering and different immunofluorescence patterns)
• Malignancy (would show cellular atypia)

Treatment Approach

First-line Treatment:

• Apply a medium to high-potency topical corticosteroid (e.g., betamethasone valerate 0.1% or clobetasol propionate 0.05%) twice daily to the affected area for 2-4 weeks 1
• Gradually taper frequency once improvement is noted (e.g., once daily for 1 week, then every other day for 1 week)

Supportive Care:

• Keep the area clean with gentle antiseptic cleansing
• Apply cold compresses intermittently for the first 24-48 hours to reduce swelling 2
• Consider oral antihistamines (e.g., cetirizine 10mg daily) if pruritus is significant 1
• Avoid scratching to prevent secondary infection

Monitoring:

• Watch for signs of secondary infection (increasing erythema, warmth, purulence, fever)
• Document the size and appearance of the lesion to track healing progress

Special Considerations

If Secondary Infection Develops:

• Take bacterial cultures before initiating antibiotics
• Consider oral antibiotics (e.g., cephalexin 500mg four times daily for 7-10 days) 1
• Continue topical corticosteroids alongside antibiotics

For Persistent or Worsening Lesions:

• Consider dermatology referral
• Re-biopsy may be necessary if the lesion persists beyond 4 weeks despite appropriate treatment

Application Technique

• Apply a thin layer of the topical corticosteroid to cover the affected area
• Use the fingertip unit method: one fingertip unit (amount from fingertip to first finger crease) covers approximately 2% body surface area 3
• Avoid occlusive dressings unless specifically directed by a dermatologist

Potential Pitfalls

• Avoid using alcohol-containing products on damaged skin as they can cause further irritation 1
• Do not forcefully rupture any intact blisters; if drainage is necessary, use sterile technique 2
• Be aware that prolonged use of high-potency topical corticosteroids can cause skin atrophy, telangiectasia, and striae 3, 4
• Monitor for signs of systemic absorption if large areas are treated with high-potency corticosteroids

The inflammatory pattern with eosinophils strongly supports an arthropod bite reaction, and appropriate treatment with topical corticosteroids should lead to resolution within 2-4 weeks.