Sweet syndrome (acute febrile neutrophilic dermatosis) !

Sudden painful red plaques with fever and high neutrophils; it may follow an infection or warn of leukaemia or a drug reaction.

Updated 2026-11-01

Structures involved

Tap one to see what it is and open it in 3D.

Why it happens

What it is

An acute neutrophilic dermatosis with abrupt onset of tender, red-to-violaceous papules, plaques or nodules, fever and neutrophilia. The skin shows a dense dermal neutrophilic infiltrate without vasculitis. It responds rapidly to systemic corticosteroids.

Who gets it

Uncommon. The classic form mainly affects women aged 30–60, often after an upper respiratory or gastrointestinal infection. Up to about one in five cases is associated with malignancy, mostly acute myeloid leukaemia, and these occur equally in men and women. No population data exist for Colombia.

Causes

Classic (idiopathic): after infections (upper respiratory, gastrointestinal), with inflammatory bowel disease or pregnancy
Malignancy-associated: acute myeloid leukaemia and myelodysplastic syndrome above all; less often solid tumours
Drug-induced: granulocyte colony-stimulating factor (G-CSF), all-trans retinoic acid, trimethoprim-sulfamethoxazole, azathioprine, some vaccines and targeted cancer drugs

Risk factors

Female sex, age 30–60 (classic form)
Recent upper respiratory or gastrointestinal infection
Haematological malignancy or myelodysplasia
Inflammatory bowel disease
Treatment with G-CSF or other implicated drugs

Pathophysiology

A hypersensitivity-like or cytokine-driven reaction (G-CSF, IL-1, IL-8 and others) recruits and activates neutrophils in the upper dermis. The result is marked papillary dermal oedema and a dense neutrophilic infiltrate without vessel wall destruction. The same process can involve extracutaneous organs such as eyes, joints, lungs and bones.

Classification

Classic or idiopathic
Malignancy-associated (paraneoplastic)
Drug-induced

Symptoms and signs

Sudden, tender, red to plum-coloured papules, plaques or nodules; plaques may look pseudovesicular or 'juicy'
Typical sites: face, neck, upper trunk and arms (dorsal hands in some)
Fever and malaise, often preceding the rash
Joint pain, conjunctivitis or episcleritis, mouth ulcers
Pathergy: lesions at sites of venepuncture or injury

Diagnosis

Clinical: Diagnostic criteria: two major (abrupt onset of tender plaques or nodules; dermal neutrophilic infiltrate without vasculitis) plus two of four minor (fever over 38 °C; associated infection, inflammatory disease, malignancy or pregnancy; raised ESR, CRP or neutrophils; excellent response to systemic corticosteroids). Drug-induced Sweet syndrome has its own criteria linking timing to the drug.
Tests: Skin biopsy with cultures to exclude infection. Complete blood count with differential and peripheral smear, ESR and CRP, liver and kidney function, urinalysis. Search for an underlying cause: age-appropriate cancer screening and bone marrow study when blood counts are abnormal.
Imaging: Chest X-ray and, when malignancy is suspected, CT of chest, abdomen and pelvis.

Differential diagnosis

Cellulitis and erysipelas
Erythema multiforme and drug eruptions
Erythema nodosum and neutrophilic panniculitis
Leukaemia cutis
Pyoderma gangrenosum (bullous form), Behçet disease and cutaneous vasculitis

Goal of treatment

Rapidly control fever, pain and skin lesions, identify and treat the trigger (infection, drug, tumour) and prevent recurrences.

Treatment

Medical: Systemic corticosteroids are first line and usually work within days, followed by a slow taper.
Medical: Alternatives or steroid-sparing agents: potassium iodide, colchicine and dapsone; topical or intralesional corticosteroids for limited disease.
Medical: Treat the cause: withdraw the culprit drug, treat infection or IBD, and refer for treatment of an associated haematological malignancy.
Follow-up: Nursing: monitor temperature, pain and blood counts, watch for steroid side effects and new lesions at puncture sites.

Complications

Recurrence (especially in malignancy-associated forms)
Extracutaneous involvement: eyes, lungs, joints, bones, kidneys
Secondary infection of lesions
Delay in diagnosing an underlying cancer

Prognosis

Lesions resolve quickly with treatment and usually heal without scarring. Recurrences occur in about a third of patients, more often in malignancy-associated cases; recurrence may herald relapse of the cancer.

Test yourself

Think of the answer, then tap the question to see it.

Which malignancy is most often associated with Sweet syndrome?

Acute myeloid leukaemia.

Which drug classically induces Sweet syndrome?

Granulocyte colony-stimulating factor (G-CSF).

What does the biopsy show?

A dense dermal neutrophilic infiltrate with papillary oedema and no vasculitis.

What is the first-line treatment?

Systemic corticosteroids, with a rapid response.

Add to my cards (4)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Acute febrile neutrophilic dermatosis (Sweet Syndrome): An Overview (DermNet, 2026).

← All conditions

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.

Skin highlighted on the Durgical 3D model