Dermatology MCQ - Inflammatory Dermatoses - Sweet syndrome

A 60-year-old woman presents with the acute onset of tender, erythematous plaques and nodules on her face, neck, and upper extremities. She also has a fever and malaise. A complete blood count reveals a neutrophilic leukocytosis. A skin biopsy of a plaque is most likely to show which of the following?

A. Non-caseating granulomas
B. Subepidermal blister with eosinophils
C. Dense dermal neutrophilic infiltrate with leukocytoclasia
D. Epidermal acantholysis and intraepidermal blisters
E. Lobular panniculitis with lipophagocytosis

Correct Answer: C. Dense dermal neutrophilic infiltrate with leukocytoclasia

Answer & Explanation

Explanation:

The clinical presentation of acute, tender, erythematous plaques with fever and neutrophilia is classic for Sweet syndrome (acute febrile neutrophilic dermatosis). The histopathology is characteristic.

• Key Histopathologic Findings:

  • Dense dermal neutrophilic infiltrate: This is the hallmark, typically located in the upper and mid-dermis.

  • Leukocytoclasia: The presence of fragmented neutrophil nuclei ("nuclear dust") is a very common feature.

  • Marked papillary dermal edema: This can be so severe that it leads to subepidermal blister formation.

  • Notable Absences: True vasculitis (fibrinoid necrosis of vessel walls) is not a feature, which helps distinguish it from leukocytoclastic vasculitis.

The other options are histologic findings for other conditions:

• A. Non-caseating granulomas: This is the hallmark of sarcoidosis and granulomatous disorders, not Sweet syndrome.

• B. Subepidermal blister with eosinophils: This is the classic finding in bullous pemphigoid.

• D. Epidermal acantholysis and intraepidermal blisters: This is characteristic of pemphigus vulgaris.

• E. Lobular panniculitis with lipophagocytosis: This describes erythema nodosum, a septal panniculitis, and other lobular panniculitides.

Key Associations for Sweet Syndrome

• Pathophysiology: A disorder of neutrophilic hyperactivity, likely due to cytokine dysregulation (e.g., G-CSF, IL-1, IFN-γ). It is considered a reactive process.

• Classification:

  • Classical (Idiopathic): Often preceded by an upper respiratory or gastrointestinal infection. More common in women.

  • Malignancy-Associated: Accounts for ~20% of cases. Most commonly associated with acute myeloid leukemia (AML), but also with other hematologic malignancies and solid tumors. It can be a paraneoplastic sign.

  • Drug-Induced: Associated with drugs like Granulocyte Colony-Stimulating Factor (G-CSF), all-trans retinoic acid, and various antibiotics.

• Clinical Presentation: The classic lesions are painful, edematous, pseudovesicular plaques that can resemble blisters but are solid. They often have a mammillated surface. Fever and arthralgias are common. Mucosal involvement can occur.

• Diagnostic Criteria (Major and 2 of 4 Minor):

  • Major: Abrupt onset of typical cutaneous lesions.

  • Minor: 1) Preceded by infection/vaccination OR associated with underlying condition (malignancy, IBD, pregnancy); 2) Fever and constitutional symptoms; 3) Leukocytosis with >70% neutrophils; 4) Excellent response to systemic corticosteroids.

• Differential Diagnosis: Includes cellulitis, erythema multiforme, urticaria, and other neutrophilic dermatoses like pyoderma gangrenosum.

• Prognosis: The classical and drug-induced forms typically resolve without scarring after treatment, but can recur. The prognosis for malignancy-associated Sweet syndrome depends on the underlying cancer.

• Management:

  • First-line: Systemic corticosteroids (e.g., prednisone 0.5-1 mg/kg/day) lead to rapid and dramatic improvement, often within days.

  • Second-line / Steroid-sparing agents: Potassium iodide, colchicine, and dapsone are highly effective alternatives.

  • For refractory or chronic cases: Immunosuppressants like cyclosporine, or biologic agents targeting IL-1 (anakinra) can be used.