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Sweet syndrome

Sweet syndrome was named after a Dr Sweet from Plymouth, England, who first described this condition in 1964. It is also known as acute febrile neutrophilic dermatosis, or simply Sweet's.

What are neutrophilic dermatoses?

Neutrophilic dermatoses are skin conditions characterised by dense infiltration of inflammatory cells (neutrophils) in the affected tissue. They arise in reaction to some underlying systemic illness. A neutrophilic dermatosis may be seen in isolation or more than one type may occur in the same individual.

Neutrophilic dermatoses often arise at the site of injury such as a needle prick, biopsy or insect bite. This reaction to injury is known as Koebner phenomenon, or isomorphic response. Pathergy refers to papules and pustules appearing at the site of needle stick.

Neutrophilic dermatoses include:

What are the symptoms of Sweet syndrome?

Sweet syndrome is an acute illness that may occur on a single occasion or may recur. It may affect previously healthy individuals, but often arises in the context of an acute systemic infection or an underlying chronic condition. Sweet syndrome most often occurs in middle-aged women, but men, children (rarely) and the elderly may also be affected.

Sweet syndrome is characterised by some or all of the following symptoms:

What do the skin lesions look like?

Skin lesions of Sweet syndrome may be few in number or numerous. They are characteristically tender and may be extremely painful. They persist for days to weeks. The limbs and neck are the most commonly affected sites, but other areas of skin and mucosa may be involved. In some patients, they arise only in sun-exposed areas. Sweet syndrome lesions may have a range of appearances.

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Sweet syndrome

Mucosal lesions

Sweet syndrome often causes erosions or ulcers inside the mouth, on the tongue or on the lips.

Ocular Sweet syndrome may cause a sore, red, sticky eye and can lead to ulceration and loss of vision due to conjunctivitis, dacryoadenitis, keratitis, episleritis, scleritis, iritis, uveitis, glaucoma and choroiditis.

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Sweet syndrome affecting mucosal surfaces

Subcutaneous Sweet syndrome

In subcutaneous Sweet syndrome, deeper, painful plaques develop on any area of skin. These may resemble cellulitis.

Neutrophilic dermatosis of hands

Neutrophilic dermatosis of the hands is considered a localised variant of Sweet syndrome in which there are purplish nodules on the backs of the thumb, fingers and hand, or less often, on palmar surfaces.

Histocytoid Sweet syndrome

Histiocytoid Sweet syndrome was first described in 2005. In this form of Sweet syndrome, instead of neutrophils, inflammation is associated with immature myeloid cell infiltration on biopsy. The name arises from the similar appearance of these monocytic cells to histiocytes. It can difficult to distinguish from leukaemia cutis.

Skin lesions typically include multiple red, purplish or brownish oval shaped patches, plaques and nodules. The rash may be persistent but may improve with successful treatment of the underlying disease or withdrawal of causative medication.

Histiocytoid Sweet syndrome has been reported in:

What causes Sweet syndrome?

Sweet syndrome develops in reaction to some internal condition, in previously well or unwell individuals. It has been found to be more common in individuals carrying the genetic marker HLA B54. Sweet syndrome may follow:

In many people with Sweet syndrome, no underlying condition is found.

How is the diagnosis made?

Sweet syndrome may be diagnosed clinically, but at times it may be difficult to distinguish from infections such as chickenpox, or inflammatory conditions such as vasculitis. The diagnosis of Sweet syndrome is usually confirmed on skin biopsy. Special stains may be necessary,

Diagnostic criteria for classic Sweet syndrome have been proposed.

Major criteria:
  1. Abrupt onset of tender or painful red or purplish plaques or nodules
  2. Biopsy shows inflammation that is composed mainly of neutrophils without vasculitis
Minor criteria:
  1. Preceding fever or infection
  2. Accompanying fever, painful joints, conjunctivitis, or underlying cancer
  3. Raised white cell count on blood testing
  4. Improvement with systemic steroids and not with antibiotics
  5. Increased erythrocyte sedimentation rate (ESR)

Diagnostic histopathological features of Sweet 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, eg mononuclear histiocyte cells rather than polynuclear neutrophil cells despite otherwise typical symptoms and signs of Sweet syndrome. True vasculitis may occur in severe cases.

Blood tests in patients with Sweet syndrome may reveal:

Occasionally Sweet 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.

What is the outcome of Sweet syndrome?

Sweets' lesions resolve eventually without leaving a mark or scar, with or without treatment.

Generally there is a single episode of Sweet syndrome, but a third of patients may develop recurrent episodes. This is more likely in patients who have underlying myelodysplasia or cancer.

Severe ulcerative cases associated with malignancy persist, despite treatment.

Treatment of Sweet syndrome

Treatment of Sweet syndrome usually results in rapid improvement in symptoms. Usually, systemic steroids, such as predniso(lo)ne, are prescribed in a dose of 30-60 mg daily. Within a few days the fever, skin lesions and other symptoms clear up. However, lower doses of steroids are often required for several weeks to months to prevent relapse.

Several other medications may be tried when steroids are ineffective or contraindicated. Those reported to be useful include:

  • Dapsone
  • Colchicine
  • Non-steroidal anti-inflammatory drugs
  • Ciclosporin
  • Biologic agents such as infliximab or etancercept
  • Minocycline
  • Mycophenolate
  • Potassium iodide solution
  • Clofazimine
  • Thalidomide
  • In some cases, Sweet syndrome is very resistant to treatment.

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