Sweet syndrome

Sweet syndrome can affect  people of any age, sex, ethnicity and skin type. In about half of cases, the cause is impossible to identify. In the other half of cases, Sweet syndrome most commonly results from upper respiratory tract or gastrointestinal infections, or reactions to medications, such as non-steroidal anti-inflammatory drugs (NSAIDs).

In some people, Sweet syndrome can result from another condition. This can include inflammatory bowel disease, lupus erythematosus or rheumatoid arthritis. In a few cases, it is a result of hormonal changes such as in pregnancy or thyroid gland disorders. More rarely, it may be a sign of cancer such as blood, breast or bowel cancer.

Classical Sweet syndrome in adults affects women more often than men. This female preponderance has not been seen in cancer-associated or drug-induced Sweet syndrome.

Most likely, the disorder results from multiple, complex factors including immunological, and environmental factors. There is also speculation that Sweet syndrome occurs as an allergic reaction (reactive process) to an unknown agent. In such instances, there is a hypersensitivity reaction by the immune system to a specific agent such as an infection, cancer, or a certain drug.

There could be a single or multiple red, pink or purplish and tender skin lumps of different sizes, occurring at any site on the body. The colour may vary across different skin tones; in brown or black skin tones, the patches may  have a subtle redness and on close look may appear dark brown, purple, or pinkish in colour. The arms, face and neck are affected most often. Sometimes, blisters or pus-filled blebs (pustules) can be seen, and the rash may appear at the site of an injury to the skin.

In some individuals, neutrophils may build up in the fatty layer of tissue just below the skin (subcutaneous fat) rather than in the dermis. Affected individuals often develop redness and small bumps (nodules) on the skin. The arms and legs are most often affected.

Sweet syndrome may cause some or all of the following symptoms arising together over a period of hours or a few days:

• a rash (described above)
• tiredness, lack of energy and feeling unwell
• high fever (temperature)
• aching joints and muscles
• mouth ulcers
• sore red eyes

Images DermNetNZ.

Tests that are useful in Sweet syndrome include:

Skin biopsy. This is an important test. A sample of the abnormal skin may be taken by your dermatologist. The skin sample is then examined under a microscope in the laboratory. It takes time for the sample to be processed and analysed by a pathologist (specialist doctor) so you will not get the result on the day.

Blood tests such as high levels of a type of white blood cells called neutrophils, can help to make a diagnosis of Sweet syndrome.

Your doctor may recommend other blood tests or imaging studies, depending on your symptoms. These may include X-ray or CT scans that look for an underlying cause of the Sweet syndrome, if suspected.

If a medication is thought to be responsible, your doctor may recommend stopping it for a while to see if this improves your symptoms.

Can Sweet syndrome be treated?

In some cases, Sweet syndrome may resolve on its own without treatment. This can take weeks to months. Due to the rarity of the condition, there are no treatment trials that have been tested on patients. Various treatments have been reported in the medical literature as part of single case reports or small series of patients. However, the condition can recur (comes back) despite therapy.

Treatments can be divided into topical and oral medications.

The skin lesions associated with Sweet syndrome usually heal without scars, unless open sores (ulcers) were present. The affected area may remain discolored for months after the lesion has been resolved.