In a 32-year-old male with multiple mosquito bites on the thighs that progressed over 20 days to a generalized pruritic papular eruption, now presenting with blurred vision and mild conjunctival redness but no fever or systemic symptoms, what is the most likely diagnosis, appropriate treatment with dosages, and differential diagnoses?

Diagnosis: Severe Mosquito Bite Allergy (SMBA) with Possible EBV-Associated NK-Cell Lymphoproliferative Disorder

The most likely diagnosis is severe mosquito bite allergy (SMBA) with systemic progression, requiring immediate workup for EBV-associated NK-cell lymphoproliferative disorder and urgent ophthalmologic evaluation for potential uveitis or EBV-related ocular complications. 1

Clinical Reasoning

This 32-year-old male presents with a classic progression pattern concerning for SMBA:

• Initial localized mosquito bites on thighs
• Progressive generalized pruritic papular eruption over 20 days
• New-onset blurred vision with conjunctival injection (mild scleral redness)
• Absence of fever or systemic pain

The temporal progression from localized to generalized reaction over weeks, combined with ocular involvement, distinguishes this from simple papular urticaria and raises concern for SMBA, which is classified within EBV-positive T/NK-cell lymphoproliferative disorders 1. The ocular findings are particularly concerning as EBV-associated disorders can cause uveitis, choroiditis, and retinal complications 2.

Immediate Diagnostic Workup Required

Critical tests to order immediately:

• EBV DNA quantitative PCR (peripheral blood) - essential for SMBA diagnosis 1
• Complete blood count with differential - assess for lymphoproliferative disorder
• Skin biopsy from papular lesion - look for angiocentric infiltration of EBV-positive NK cells 1
• Comprehensive ophthalmologic examination - assess for uveitis, retinitis, or other EBV-related complications 2
• Specific IgE testing to mosquito salivary antigens if available 3

Treatment Protocol

Immediate Management (Start Today):

Primary regimen:

• Oral prednisone 40-60 mg daily (0.5-1 mg/kg) for severe SMBA 1
• Cetirizine 20 mg once daily (double standard dose for mosquito allergy) 4, 5
• Valacyclovir 1000 mg daily (for potential EBV reactivation) 5

Adjunctive therapy:

• Topical clobetasone butyrate 0.05% to papular lesions twice daily 6
• Cold compresses and refrigerated preservative-free artificial tears for ocular symptoms 2
• Emollients liberally to all affected areas 6

Steroid-Sparing Alternative (if prolonged treatment needed):

If the patient requires extended management or has contraindications to prolonged corticosteroids, consider the steroid-sparing regimen that has shown success in similar cases 5:

• Doxycycline 100 mg twice daily
• Cetirizine 20 mg once daily
• Valacyclovir 1000 mg daily

This combination resulted in sustained reduction in bullous eruptions in a documented case of MCL-associated exaggerated mosquito bite reactions 5.

Differential Diagnoses (In Order of Likelihood)

1. Severe Mosquito Bite Allergy (SMBA) with EBV-associated NK-cell LPD - Most likely given progressive generalized reaction and ocular involvement 1

2. Papular Urticaria - Common in adults following mosquito bites, but typically doesn't progress to generalized distribution or cause ocular symptoms 7, 8

3. Skeeter Syndrome - Large local inflammatory reactions to mosquito bites with systemic symptoms, but usually more acute onset 3

4. Wells' Syndrome (Eosinophilic Cellulitis) - Can present with exaggerated mosquito bite reactions and robust CD4+ T cell proliferation, but typically lacks ocular involvement 9

5. Acute Generalized Exanthematous Pustulosis (AGEP) - Rare trigger by mosquito bites, but presents with sterile pustules rather than papules 10

6. Viral Conjunctivitis (Zika, EBV, or other arbovirus) - Mosquito-borne transmission possible, but wouldn't explain the progressive generalized papular eruption pattern 2

7. Systemic Lupus Erythematosus flare - Mosquito bites can trigger SLE flares with targetoid rash, but patient lacks other SLE features 11

8. Underlying Hematologic Malignancy (MCL or other B-cell neoplasm) - Can present with exaggerated mosquito bite reactions 9, 5

Critical Pitfalls to Avoid

Do not dismiss the ocular symptoms - The combination of progressive generalized reaction with ocular involvement suggests systemic disease beyond simple hypersensitivity. EBV-associated disorders can cause sight-threatening complications including retinitis, choroiditis, and optic neuritis 2.

Do not use topical corticosteroids on the eyes without ophthalmology consultation - Corticosteroids can worsen certain viral infections and should only be used under specialist guidance for ocular symptoms 2.

Do not delay EBV testing - SMBA is recognized as a specific cutaneous manifestation of chronic active EBV disease with potential progression to overt T/NK-cell leukemia or lymphoma 1. Early detection is critical.

Avoid indiscriminate antibiotic use - Unless secondary bacterial infection is evident, antibiotics are not indicated for mosquito bite reactions 2.

Follow-Up Protocol

• Ophthalmology referral within 24-48 hours for comprehensive eye examination
• Hematology referral if EBV DNA load is elevated or CBC shows abnormalities
• Reassess in 3-5 days to evaluate treatment response
• Monitor for progression to necrotic ulcers, bullae, or systemic symptoms (fever, lymphadenopathy) which would indicate more aggressive disease 1
• Long-term surveillance if EBV-positive, as these patients require monitoring for progression to lymphoma 1

The elderly-onset case reported in 2026 demonstrated that even with high EBV loads, patients can maintain stable, indolent courses with appropriate treatment 1, making early diagnosis and management crucial for optimal outcomes.