How do you diagnose Sweet syndrome?

Diagnosing Sweet Syndrome

Sweet syndrome (acute febrile neutrophilic dermatosis) is diagnosed through a combination of clinical presentation, laboratory findings, and histopathological examination of skin lesions, with skin biopsy being the definitive diagnostic test.

Clinical Presentation

• Sweet syndrome presents with a characteristic triad of:

  • Tender, erythematous papules, nodules, or plaques commonly appearing on the upper limbs, trunk, and head/neck 1, 2
  • Fever (present in approximately 32% of cases) 3
  • Neutrophilia and elevated inflammatory markers 4

• The skin lesions typically appear suddenly and are:

  • Painful or tender to touch 2
  • Erythematous with well-defined borders 4
  • May have a pseudovesicular or pustular appearance 2
  • Most commonly located on upper extremities and trunk 3

Laboratory Findings

• Blood tests often reveal:
  • Leukocytosis (present in about 60% of patients) 3
  • Neutrophilia (present in about 39% of patients) 3
  • Elevated inflammatory markers (ESR, CRP) 4
  • Lower hemoglobin levels may suggest malignancy-associated Sweet syndrome 3

Diagnostic Criteria

• Diagnosis requires both major criteria and at least two minor criteria:

  • Major criteria:

    • Abrupt onset of painful erythematous plaques or nodules 2
    • Histopathology showing dense neutrophilic infiltrate in the dermis without leukocytoclastic vasculitis 2, 4

  • Minor criteria:

    • Fever >38°C 2
    • Association with underlying malignancy, inflammatory disease, pregnancy, or preceding infection or vaccination 2
    • Excellent response to systemic corticosteroids or potassium iodide 2
    • Abnormal laboratory values (elevated ESR, positive CRP, leukocytosis, neutrophilia) 2, 3

Skin Biopsy

• Skin biopsy is the definitive diagnostic test for Sweet syndrome and should be performed on an active lesion 1, 4
• Histopathological findings include:
  • Dense neutrophilic infiltrate in the upper dermis 2
  • Edema of the papillary dermis 3
  • Absence of vasculitis (though leukocytoclasia may be present) 3
  • Lymphohistiocytic infiltrate may also be present 3

Clinical Variants and Associations

• Sweet syndrome presents in three clinical settings:

  • Classical/idiopathic (53% of cases) - often preceded by upper respiratory infection 5
  • Malignancy-associated (35% of cases) - most commonly associated with hematologic malignancies 5
  • Drug-induced (12% of cases) - most commonly associated with G-CSF 2, 5

• Important associations to investigate:

  • Malignancies (particularly acute myelogenous leukemia) 2
  • Inflammatory bowel disease 1
  • Recent infections (especially upper respiratory) 2
  • Medications (G-CSF most common) 2
  • Pregnancy 2

Differential Diagnosis

• The differential diagnosis should include:
  • Drug eruption 1
  • Cutaneous infiltration with underlying malignancy 1
  • Chemotherapy or radiation-induced skin reactions 1
  • Erythema multiforme 1
  • Leukocytoclastic vasculitis 1
  • Infection (bacterial, fungal, viral, parasitic) 1

Diagnostic Approach

1. Perform thorough clinical examination of skin lesions 1
2. Obtain laboratory tests: CBC with differential, ESR, CRP 4
3. Perform skin biopsy for histopathological examination 1
4. Screen for underlying conditions, especially if anemia or elevated ESR is present 3
5. Review medication history for potential triggers 2
6. Consider additional workup based on clinical suspicion (e.g., chest X-ray, blood cultures if infection suspected) 4

Pitfalls to Avoid

• Failure to perform skin biopsy, which is essential for definitive diagnosis 1
• Overlooking potential underlying malignancy, especially in patients with anemia 3
• Missing drug-induced causes, which require medication discontinuation 2
• Confusing with other neutrophilic dermatoses or infectious processes 1
• Not recognizing atypical presentations or variants of Sweet syndrome 4

Remember that patients with leukocytoclasia on biopsy may have a higher risk of recurrence and require closer follow-up 3.