What is the approach to diagnosing and treating Sweet syndrome in pediatric patients?

Diagnosis of Sweet Syndrome in Children

Sweet syndrome in pediatric patients should be diagnosed based on the characteristic clinical triad of tender erythematous papules/nodules/plaques, fever, and neutrophilia, confirmed by skin biopsy showing dense dermal neutrophilic infiltrate without vasculitis. 1

Clinical Presentation

The diagnosis begins with recognizing the distinctive clinical features:

• Skin lesions appear as tender, erythematous papules, nodules, or plaques that develop rapidly over 24-48 hours, most commonly on the upper limbs, trunk, and head/neck regions 1, 2
• Fever is a consistent presenting feature in pediatric cases 2, 3
• Systemic inflammation manifested by markedly elevated neutrophil counts (often >40,000/mm³) and elevated inflammatory markers (CRP, ESR) 2, 3

Essential Diagnostic Steps

Skin Biopsy - The Definitive Test

Skin biopsy of an active lesion is mandatory for definitive diagnosis and should never be omitted. 1 The histopathology must demonstrate:

• Dense dermal infiltrate of mature neutrophils diffusely distributed in the upper dermis 4, 5
• Absence of leukocytoclastic vasculitis (which distinguishes it from vasculitis) 1
• No evidence of infection on tissue culture 1

Failure to perform skin biopsy leads to misdiagnosis, as the clinical presentation can mimic multiple other conditions 1.

Laboratory Evaluation

Complete the following workup at presentation:

• Complete blood count with differential showing neutrophilia (absolute neutrophil count typically markedly elevated) 2, 3
• Inflammatory markers including CRP and ESR (typically significantly elevated) 2
• Blood cultures if infection is suspected 1

Critical Differential Diagnosis

You must systematically exclude these conditions that can mimic Sweet syndrome:

• Drug eruption - obtain detailed medication history 1
• Infection (bacterial, fungal, viral, parasitic) - perform appropriate cultures and serologies 1
• Cutaneous infiltration from malignancy - particularly important in pediatrics where hematologic malignancies are the most common associated cancers 3
• Erythema multiforme - distinguished by target lesions and different histology 1
• Leukocytoclastic vasculitis - excluded by absence of vasculitis on biopsy 1
• Bowel-associated dermatosis-arthritis syndrome - distinguished by presence of ulceration and different distribution 1

Evaluation for Underlying Conditions

In 50-70% of pediatric Sweet syndrome cases, an underlying systemic disorder is present, requiring systematic evaluation. 1

Infection Screening (Most Common in Pediatrics)

Pediatric Sweet syndrome is more frequently associated with infections than malignancies, unlike adults 3:

• Mycoplasma pneumoniae testing (serology, PCR) - specifically associated with mucous membrane-predominant variant 1
• Upper respiratory tract infection evaluation 1, 2
• Other bacterial, viral, and fungal cultures as clinically indicated 1

Malignancy Screening

Although less common than in adults, hematologic malignancies must be excluded 3:

• Complete blood count with peripheral smear review
• Bone marrow evaluation if hematologic abnormalities present beyond neutrophilia 3
• Acute myelogenous leukemia is the most common associated malignancy when present 5

Inflammatory Bowel Disease Evaluation

The American Gastroenterological Association recommends evaluating for underlying IBD, particularly ulcerative colitis and Crohn's disease, as Sweet syndrome is part of the spectrum of neutrophilic dermatoses in IBD 1.

Common Diagnostic Pitfalls

• Treating empirically as bacterial infection without biopsy confirmation - Sweet syndrome often fails to respond to antibiotics, leading to diagnostic delay 2
• Missing the diagnosis in immunocompromised patients or those with chromosomal abnormalities who may present atypically 2
• Failing to screen for underlying conditions - particularly infections in children, which are the most common trigger 3
• Confusing with bullous impetigo when bullous lesions are present - biopsy distinguishes these entities 2

Diagnostic Algorithm Summary

1. Clinical recognition: Tender erythematous plaques + fever + rapid onset over 24-48 hours
2. Laboratory confirmation: CBC showing neutrophilia, elevated inflammatory markers
3. Histologic confirmation: Skin biopsy showing dense dermal neutrophilic infiltrate without vasculitis
4. Exclude infection: Cultures, serologies (especially Mycoplasma)
5. Screen for malignancy: Peripheral smear, consider bone marrow if abnormalities present
6. Evaluate for IBD: Particularly if gastrointestinal symptoms present