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# 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.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Radius](https://durgical.com/en/anatomy/radius/)
- [Ulna](https://durgical.com/en/anatomy/ulna/)
- [Platysma](https://durgical.com/en/anatomy/platysma/)

## Why it happens

- [White blood cells: types and functions](https://durgical.com/en/physiology/white-blood-cells-types-and-functions/)
- [Skin: epidermis layers, dermis, hypodermis](https://durgical.com/en/histology/skin-epidermis-layers-dermis-hypodermis/)

## 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

## Red flags

- Anaemia, thrombocytopenia, blasts or unexplained cytopenias (suspect leukaemia or myelodysplasia)
- Bullous or ulcerated lesions (more often malignancy-associated)
- Recurrence after treatment or no obvious trigger in an older patient
- Breathlessness, eye pain or organ involvement

## 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](https://durgical.com/en/anatomy/skin/) biopsy with cultures to exclude infection. Complete blood count with differential and peripheral smear, ESR and CRP, [liver](https://durgical.com/en/anatomy/liver/) and [kidney](https://durgical.com/en/anatomy/kidney/) function, urinalysis. Search for an underlying cause: age-appropriate cancer screening and bone marrow study when blood counts are abnormal.

**Imaging**
[Chest](https://durgical.com/en/anatomy/region/chest/) X-ray and, when malignancy is suspected, CT of chest, [abdomen](https://durgical.com/en/anatomy/region/abdomen/) and [pelvis](https://durgical.com/en/anatomy/region/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.

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## Related conditions

- [Acute leukaemia (AML and ALL)](https://durgical.com/en/conditions/acute-leukaemia/)
- [Myelodysplastic syndromes](https://durgical.com/en/conditions/myelodysplastic-syndromes/)
- [Paraneoplastic syndromes](https://durgical.com/en/conditions/paraneoplastic-syndromes/)
- [Pyoderma gangrenosum](https://durgical.com/en/conditions/pyoderma-gangrenosum/)
- [Erythema nodosum](https://durgical.com/en/conditions/erythema-nodosum/)
- [Erythema multiforme](https://durgical.com/en/conditions/erythema-multiforme/)
- [Ulcerative colitis](https://durgical.com/en/conditions/ulcerative-colitis/)
- [Crohn disease](https://durgical.com/en/conditions/crohn-disease/)

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

Sources: [Acute febrile neutrophilic dermatosis (Sweet Syndrome): An Overview](https://dermnetnz.org/topics/acute-febrile-neutrophilic-dermatosis) (DermNet, 2026).

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Source: https://durgical.com/en/conditions/sweet-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/sweet-syndrome/