Sweet syndrome is a rare inflammatory condition. It involves a sudden onset of fever and painful skin rashes.

Sweet syndrome, or acute febrile neutrophilic dermatosis, is a rare skin condition. It takes its name from Dr. Robert Douglas Sweet, who first described the condition in 1964.

The condition falls under neutrophilic dermatosis, a group of skin conditions characterized by the accumulation of neutrophils in the skin.

Neutrophils are white blood cells that act as the immune system’s first line of defense against infections.

This article explores Sweet syndrome, its causes, symptoms, and treatment.

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Sweet syndrome is a rare type of inflammatory skin disorder. People with the syndrome experience an abrupt appearance of tender, red, swollen, and painful bumps on their trunk, arms, face, and neck.

Fever and an increased white blood cell count often accompany skin lesions. A person may also feel generally ill.

Most people with the condition have no known cause. Sometimes, Sweet syndrome may occur in people with cancer or as a side effect of certain drugs.

It is more likely to affect females than males and typically begins between the ages of 30 to 60.

The exact cause of Sweet syndrome is not clear. However, multiple factors, such as genetic, environmental, and immunological factors, may play a role.

It is more common in people carrying the genetic marker HLA-B54.

Experts consider Sweet syndrome to be a “reactive” or allergic condition.

They believe that an unknown agent, such as a virus, bacteria, cancer, or drug, triggers an allergic reaction from a hypersensitive or oversensitive immune system.

Malfunctioning cytokines may also play a role in the development of the condition. Cytokines are specialized proteins that either promote or inhibit the function of other immune system cells.

Examples of cytokines involved in immune-related hypersensitivity include:

  • interleukin-1β (IL-1β)
  • IL-17
  • tumor necrosis factor-α (TNF-α)

People with this syndrome also have an elevated neutrophil count.

There are three subtypes of Sweet syndrome:

  • idiopathic or classical Sweet syndrome — no identified cause
  • malignancy-associated Sweet syndrome — caused by an underlying cancer
  • drug-induced Sweet syndrome — triggered by certain drugs

Classical Sweet syndrome

Causes of classical Sweet syndrome include:

In some cases, the following autoimmune disorders may play a role:

Malignancy-associated Sweet syndrome

Some people with Sweet syndrome have underlying cancers. Symptoms of the syndrome may occur before, at the time of, or after a person receives a cancer diagnosis.

The most common cancers associated with Sweet syndrome are blood cancers.

Drug-induced Sweet syndrome

Certain drugs may also cause the condition. The most common is granulocyte colony-stimulating factor (G-CSF), a cancer drug that stimulates neutrophil production.

Other drugs that may lead to Sweet syndrome include:

The primary symptoms of Sweet syndrome are well-defined, tender, and red or bluish bumps or lesions.

The bumps grow slowly and eventually join together, or coalesce, to form larger plaques.

They appear red, inflamed, irregularly shaped, and may be flat or raised. These mainly tend to occur on a person’s:

  • arms
  • legs
  • trunk
  • face
  • neck
  • thighs

People with Sweet syndrome often have other symptoms accompanying the skin lesions including:

It may also affect other organs, such as their:

Generally, a dermatologist diagnoses the condition based on a detailed history, clinical evaluation, and observation of the classic symptoms of Sweet syndrome.

Most of the time, a doctor will take a skin sample through a biopsy and analyze it under a microscope to check for neutrophil infiltrates in the dermis.

They may also order:

In order for a doctor to diagnose a person with Sweet syndrome, two significant findings must be present: a sudden eruption of tender, painful nodules or plaques and neutrophilic infiltrate in the dermis.

In addition, at least two of the four following criteria must also be present for a diagnosis:

  • a temperature greater than 38°C (100°F)
  • an upper respiratory or gastrointestinal infection precedes the condition, or it is linked with an inflammatory disease, pregnancy, or cancer
  • an elevated white blood cell count with a neutrophilic predominance and elevated inflammatory markers
  • the person responds well to corticosteroids

A doctor may also perform other tests to identify the condition’s underlying cause, including:

  • a cancer screening
  • a chest, abdominal, and pelvic CT scan
  • a pregnancy test

When Sweet syndrome is not due to an underlying cause, it often resolves on its own and responds well to steroids.

Doctors usually give a person a 2 to 4-week tapering course of oral prednisone, beginning at a daily dose of 40–60 milligrams. These drugs are also available as injections.

A doctor may prescribe other drugs if the symptoms recur after the person is off the steroids.

A small 2019 study found people with the condition responded well to immunosuppressants.

Other possible treatments include:

Lesions tend to return in 30% of people with Sweet syndrome. Often, recurrence occurs in people with an underlying malignancy.

The following can help prevent recurrences and further damage to the skin:

  • gently cleaning lesions and avoiding adhesive tapes to secure the dressings
  • avoiding UV light, which may trigger lesions
  • avoiding overexposure to strong sunlight and sunbeds
  • using protective clothing and avoiding the outdoors when the sun is the strongest

Sweet syndrome, or acute febrile neutrophilic dermatosis, is a rare inflammatory condition that causes the sudden appearance of red, painful bumps and lesions accompanied by symptoms, such as fever and general malaise.

Most of the time, there is no known cause. However, the condition may result from an underlying condition, such as cancer or autoimmune disorders.

When Sweet syndrome isn’t due to an underlying condition, it is generally self-limiting and tends to resolve on its own. It also responds well to treatment.