Sweet Syndrome

Sweet syndrome (acute febrile neutrophilic dermatosis) is an inflammatory disorder characterised by fever, neutrophilia, and tender erythematous papules or plaques with dense neutrophilic dermal infiltrate.

• Types: classical (idiopathic, often after infection or with IBD or pregnancy), malignancy associated (20%, usually AML and MDS), and drug induced (G-CSF, azacitidine, bortezomib, all-trans retinoic acid, minocycline, hydralazine, furosemide, TMP-SMX, immune checkpoint inhibitors).
• Women aged 30 to 60 most commonly affected in classical forms.
• Pathogenesis involves cytokine dysregulation (IL-1, IL-6, G-CSF) and genetic factors (MEFV, UBA1 in some).

• Abrupt onset of painful (not itchy) red or violaceous papules, nodules, or plaques with a "juicy" pseudovesicular surface, on face, neck, upper trunk, and arms.
• Fever (above 38 degrees Celsius), malaise, myalgia, arthralgia, and conjunctivitis or episcleritis.
• Pathergy may occur; bullous or necrotic variants point to haematological disease.
• Extracutaneous: sterile neutrophilic infiltration of lungs, kidneys, bone, and CNS.

• Von den Driesch criteria: both major (abrupt onset of painful erythematous plaques; dense neutrophilic infiltrate without leukocytoclastic vasculitis) plus two of four minor (preceding infection or vaccination, fever above 38 degrees Celsius, associated malignancy or inflammatory disease or pregnancy, leucocytosis with neutrophilia, excellent response to systemic steroids).
• Biopsy: dense dermal neutrophilic infiltrate with papillary dermal oedema.
• Investigations: FBC with differential and blood film, ESR, CRP, creatinine, urinalysis, and chest X-ray.
• Screen for malignancy (haematological malignancy if cytopenias or atypical cells), IBD, and infections (streptococcus, Yersinia); review drug history.
• Exclude cellulitis, erythema nodosum, pyoderma gangrenosum, and Behçet disease.

• Treat underlying cause (malignancy, infection, withdrawal of drugs).
• First line: prednisolone 0.5 to 1 mg/kg/day for 4 to 6 weeks with slow taper over 4 to 6 weeks; rapid response in 24 to 72 hours.
• Localised disease: clobetasol 0.05% or intralesional triamcinolone 10 mg/mL.
• Steroid sparing: colchicine 0.5 mg two to three times daily, potassium iodide 300 mg three times daily (900 mg/day), dapsone 100 to 200 mg daily.
• Resistant disease: indomethacin 150 mg/day for 1 week then 100 mg/day for 2 weeks, ciclosporin 2 to 4 mg/kg, anakinra 100 mg daily, canakinumab, or TNF inhibitors.
• Recurrence in about 30%; follow up for haematological malignancy for at least 1 to 2 years.