How is Sweet’s syndrome diagnosed?

Updated 24/11/18.

For doctors, please see ‘Medical information’ and ‘Additional note’ for proposed changes to diagnostic criteria by Nofal et al.

Patient information.

1. A diagnosis of Sweet’s syndrome is made by taking your medical history to see if you have had any infections, other health conditions, are pregnant, or are taking any medications that could trigger it.

2. Almost all Sweet’s syndrome patients have skin lesions, but there are many different lesion types. This means that Sweet’s syndrome can’t be diagnosed via visual examination alone. Your doctor or specialist will need to take a biopsy (tissue sample) of a lesion for detailed microscopic examination to confirm diagnosis, and rule out any other conditions that might be confused with Sweet’s syndrome. On rare occasions, skin lesions aren’t present.

3. Your temperature will be taken. Sweet’s syndrome normally causes an unexplained fever of 38 degrees Centigrade (100.4 degrees Fahrenheit) or above. Sometimes, a fever isn’t present.

4. Blood tests will be needed to detect any inflammation in the body, and some additional blood tests will be needed to rule out cancer and possibly other conditions as a trigger for Sweet’s syndrome.


In approximately 20% of cases, Sweet’s syndrome can develop secondary to blood cancer and other forms of cancer. This is called malignancy-associated Sweet’s syndrome (MASS). Myelodysplasia, otherwise known as myelodysplastic syndromes (MDS), is one of the most common causes of MASS.

In all patients with Sweet’s syndrome, cancer needs to be ruled out as a trigger, and you should be checked for MDS via blood tests for at least 6 months after receiving your diagnosis. Unfortunately, this isn’t always happening, so if you have Sweet’s syndrome, you might want to check with your doctor that this is going to be done or has been done.

Medical information.

Main diagnostic criteria (Oakley, 2015).

Major criteria.

  • Abrupt onset of tender or painful red or purplish plaques or nodules.
  • Biopsy shows inflammation that is composed mainly of neutrophils without vasculitis.

Minor criteria.

  • Preceding fever or infection.
  • Accompanying fever, painful joints, conjunctivitis, or underlying cancer.
  • Raised white cell count on blood testing.
  • Improvement with systemic steroids and not with antibiotics.
  • Increased erythrocyte sedimentation rate (ESR).

Diagnostic histopathological features of Sweet’s syndrome are numerous polynuclear neutrophil inflammatory cells on skin biopsy associated with broken-up neutrophils (leukocytoclasia) and swelling of cells lining blood vessels (endothelial cells). However, other inflammatory patterns may be observed, e.g. mononuclear histiocyte cells rather than polynuclear neutrophil cells, despite otherwise typical symptoms and signs of Sweet’s syndrome. True vasculitis may occur in severe cases.

Blood tests in patients with Sweet’s syndrome may reveal:

  • Raised erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), indicating systemic inflammatory disease.
  • Raised white cell count (neutrophil leukocytosis).
  • p-ANCA (antineutrophil cytoplasmic antibody) or c-ANCA is sometimes present.

Occasionally, Sweet’s syndrome is the presenting sign of a serious blood condition. A full blood count may reveal raised or reduced numbers of red cells, white cells and/or platelets. Further investigation may require bone marrow examination.

Additional note.

Nofal et al have argued that the major criteria should be viewed as ‘constant features’ and the minor criteria as ‘variable features’, and that none of the minor criteria needs to be met for a diagnosis of Sweet’s syndrome to be given (Nofal et al, 2017).

Further information – patients.

Autoinflammatory Alliance (2015) Autoinflammatory Disease Comparison Chart (online). Accessed 24/11/18.

GARD (2016) Acute Febrile Neutrophilic Dermatosis. Genetic and Rare Diseases Information Center, NIH (online). Accessed 24/11/18. A good starting point to learn more about Sweet’s syndrome.

Melao, A. (2018) Symptoms of Sweet’s Syndrome May Include Higher Levels of ANCA Autobodies, Case Report Suggests. ANCA Vasculitis News, Feb 19 (online). Accessed 24/11/18.

Three Unusual Cases of Sweet’s Syndrome Where Skin Lesions Where the Only Symptom. In Case 3, ESR and CRP were normal.

Tousseau, J. and Durrant, K. (2015) Periodic Fever Syndromes in Adults. Autoinflammatory Alliance (SAID Support blog), Oct 28th (online).

Variants of Sweet’s Syndrome. Sometimes, Sweet’s syndrome can occur in an unusual form, and this is known as a disease variant. If you have a variant of Sweet’s syndrome, this can make it more difficult to diagnose.

Further information – medical.

Arun Kumar, A.U., Elsayed, M.E., Alghali, A., Ali, A.A., Mohamed, H., Hussein, W., Hackett, C., Leonard, N. and Stack, A.G. (2018) Sweet syndrome: a rare feature of ANCA-associated vasculitis or unusual consequence of azathioprine-induced treatment. Allergy, Asthma, and Clinical Immunology: Official Journal of the Canadian Society of Allergy and Clinical Immunology, Nov 8;14:46 (PMC).

Cohen, P. (2007) Table 1: Diagnostic criteria for classical Sweet’s syndrome versus drug-induced Sweet’s syndrome. In Sweet’s syndrome – a comprehensive review of an acute febrile neutrophilic dermatosis (PDF).

Kaballo, M. (2016) Sweet’s Syndrome and the Kidney. Renal Fellow Network, Apr 18 (online). Includes information on possible causes for a positive ANCA test in Sweet’s syndrome.

Media – medical.

McColl, I. (2013) Sweet’s Syndrome: Clinical and Histopathological Variants (You Tube Video).


Nofal, A., Abdelmaksoud, A., Amer, H., Nofal, E., Yosef, A., Gharib, K., Albalat, W., Eldesouky, F., Ebrahim, H., Abdelshafy. A. and  Fayed, H. (2017) Sweet’s syndrome: diagnostic criteria revisited. Journal der Deutschen Dermatologischen Gesellschaft = Journal of the German Society of Dermatology: JDDG, Nov;15(11):1081-1088 (Wiley).

Oakley, A. (2015) Acute Febrile Neutrophilic Dermatosis. DermNet NZ (online). Accessed 24/11/18.

2012-present, Sweet’s Syndrome UK


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