What causes Sweet’s syndrome?
Autoinflammatory conditions such as Sweet’s syndrome are caused by errors in the innate immune system, the body’s most primitive, ‘hard-wired’ immune system, and a part of the immune system that doesn’t produce antibodies. However, Sweet’s syndrome itself is still a poorly understood condition, but specific causes, i.e. what happens in the body that leads to the symptoms of Sweet’s syndrome, includes hypersensitivity reaction, cytokine dysregulation, and genetic susceptibility.
1. Hypersensitivity reaction.
Because of errors in the innate immune system, in some people with Sweet’s syndrome, their immune system responds to antigens in a way that it shouldn’t, i.e. is hypersensitive and goes into overdrive, overreacting to the presence of infectious, inflammatory, drug, or tumour cell antigens (Bhat et al, 2015: 257; Kasirye et al, 2011: 135).
Antigens are mainly proteins or sugars on the surface of a cell or a non-living substance, that a part of your immune system called the adaptive immune system sees as a foreign invader and produces antibodies in response to. The presence of antigens associated with certain health conditions, medications and vaccinations, can potentially trigger Sweet’s syndrome by stimulating the innate immune system to produce cytokines (see ‘Cytokine dysregulation’), which eventually leads to the activation of white blood cells called neutrophils (Gosheger et al, 2002: 70). The neutrophils migrate to skin tissues and sometimes other tissues, causing skin lesions or other symptoms of Sweet’s syndrome.
Potential triggers for Sweet’s syndrome include:
- Cancer and blood disorders (malignancy-associated or paraneoplastic) in 15-20% of cases, e.g. solid tumours, and myelodysplastic syndrome which may progress to acute myeloid leukaemia (Chen et al, 2016).
- Infection, particularly upper respiratory tract and gastrointestinal infection, but others infections too (Cohen, 2007).
- Inflammatory bowel disease, e.g. Crohn’s disease and ulcerative colitis.
- Autoimmune conditions, e.g. rheumatoid arthritis and systemic lupus erythematosus (Ibid).
- Medications (drug-induced) in 5%-12% of cases.
- Vaccination. This is very rare – only 11 cases reported in medical literature in the past 42 years, globally – and a definite connection has not been established between the Sweet’s syndrome and vaccination in some of those cases.
Other potential yet very poorly understood triggers for Sweet’s syndrome include:
- Pregnancy (pregnancy-associated) in up to 2% of cases. This is probably associated with hormonal changes, but further research is required. On rare occasions, Sweet’s syndrome can also be triggered by the contraceptives, levonorgestrel/ethinyl estradiol (Triphasil) and levonorgestrel-releasing intrauterine system (Mirena) (Cohen, 2007).
- Skin damage. When the skin is damaged or irritated, this can sometimes trigger the development of skin lesions, and this is known as pathergy. Potential irritants can even include natural products such as arnica cream (Shenefelt, 2011).
- Overexposure to sunlight or ultraviolet (UV) light. This can sometimes trigger Sweet’s syndrome, but we are not entirely sure why this happens.
Overall, in up to 71% of cases, there is no known trigger or underlying condition in Sweet’s syndrome (Tam and Ingraffea, 2015). However, Resende et al state that it is only in up to 50% (Resende et al, 2016). One of the reasons that these figures may vary is because in some countries Sweet’s syndrome is more likely to develop secondary to infection (Ginarte and Toribio, 2011:120).
Cytokines are proteins and molecular messengers and part of the body’s immune system. The overproduction or inappropriate production of cytokines, known as cytokine dysregulation, can result in disease. Cytokines involved in Sweet’s syndrome include:
Endogenous granulocyte colony-stimulating factor.
- Endogenous G-CSF is a cytokine that is produced by the body, and is associated with an increased white blood cell count and skin lesions in Sweet’s syndrome patients (Ozlem et al, 2011: 1975).
- Research shows that patients with active Sweet’s syndrome have higher G-CSF levels than those whose disease is inactive, and G-CSF therapy (a treatment that helps you make more white blood cells) can trigger Sweet’s syndrome (Ginarte and Toribio, 2011; Kawakami et al, 2004; Paydas, 2013: 87).
- An increased production of G-CSF caused by cancer cells is a factor in malignancy-associated Sweet’s syndrome (Foster et al, 2005: 145, 148). Research shows that blood cancers such as leukaemia cause an increase in interleukin 1/IL-1 (see ‘Other cytokines’) which affects G-CSF levels. G-CSF then recruits neutrophils to the skin via interleukin 6/IL-6 (Yang et al, 2017).
- Granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon gamma, and interleukins (IL-) 1, 2, 3, 6, and 8 can play a role in Sweet’s syndrome (Bhat et al, 2015: 527; Ginarte and Toribio, 2011; Kumar et al, 2004; Paydas, 2013: 87; Takano et al, 2017).
- Increased levels of IL-6 have been linked to fever and pain in patients (Ozlem et al, 2011: 1975).
- IL-6 may play a role in Sweet’s syndrome that has developed secondary to the autoimmune disease systemic lupus erythematosus. This is due to IL-6 and other cytokines being a factor in both conditions (Barton et al, 2011: 5).
3. Genetic susceptibility.
Sweet’s syndrome is not a genetic condition, but may be associated with certain genes and abnormalities. These include:
The genetic marker HLA-B54.
HLA-B54 is more likely to be found in people with Sweet’s syndrome, but is rare in the similar condition Behcet’s disease (Hisanaga et al, 1999). The frequency of HLA-B54 is higher in Japanese (17.9%) compared with white (0.6%) or black (0%) populations, suggesting a genetic predisposition among the Japanese for Sweet’s syndrome (Bellus and Stumpf, 2003).
Abnormalities in chromosome 3q.
Structural abnormalities in chromosome 3q in bone marrow cells of two patients with Sweet’s syndrome and myelodysplastic syndrome or acute myeloid leukaemia (Billstrom et al, 1990).
Protein tyrosine phosphatase non-receptor type 6 (PTPN6) gene.
A mutation in the protein tyrosine phosphatase non-receptor type 6 (PTPN6) gene has been linked to some types of neutrophilic dermatoses, including Sweet’s syndrome (Gurung and Kanneganti, 2016; Li et al, 2015: 341).
Possible MEFV gene mutation.
Possibly MEFV gene mutation causing Sweet’s syndrome in patients who have developed their condition secondary to myelodysplastic syndromes (Jo et al, 2015 ). However, there is some debate concerning whether or not this is accurate, and Koné-Paut et al have argued that this theory as ‘premature or even misleading’ (Koné-Paut et al, 2015). MEFV mutations are also the cause for the autoinflammatory condition familial Mediterranean fever.
Autoinflammatory conditions such as Sweet’s syndrome are caused by errors in the innate immune system.
Sweet’s syndrome is still a poorly understood condition, but specific causes include hypersensitivity reaction, cytokine dysregulation, and genetic susceptibility.
Hypersensitivity reaction is when the presence of antigens associated with certain health conditions, medications and vaccinations, trigger Sweet’s syndrome by stimulating the innate immune system to produce molecular messengers called cytokines. This eventually leads to the activation of white blood cells called neutrophils.
Over-production or inappropriate production of cytokines, otherwise known as cytokine dysregulation, has been proven to lead to the symptoms of Sweet’s syndrome.
Sweet’s syndrome has been linked to the genetic marker HLA-B54.
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