Pathergy and skin sensitivity in Sweet’s syndrome

Updated on 23/08/2017.

Some people with Sweet’s syndrome seem to be very sensitive to skin damage – why is this?

Doctors and researchers don’t know why some people with Sweet’s syndrome are more sensitive to skin damage than others, but we do know that it can be a pathergy response. This is an unusual response that is sometimes referred to as Koebner phenomenon or isomorphic response, but even though they are similar, they are not exactly the same thing.

What is Koebner phenomenon or isomorphic response?

The Koebner phenomenon or isomorphic response is named after the German dermatologist Heinrich Koebner (1838–1904) who first recognised it in psoriasis patients. It is a phenomenon that causes skin lesions to appear at the site of a skin injury in otherwise healthy skin. In patients demonstrating a true Koebner response, this phenomenon can be confirmed by experimentally reproducing lesions with different methods of injury. These lesions will then normally appear in a linear shape, i.e. in lines (Luo, 2014).

In which conditions can Koebner phenomenon be seen?

Koebner phenomenon is most commonly seen in those with psoriasis, vitiligo and lichen planus, but can occasionally be seen in other conditions too. In July 2017, Koebner phenomenon was reported in a 68-year-old female patient with Sweet’s syndrome whose lesions developed on a linear scar (Chern et al, 2017).

Can it occur for reasons other than health conditions?

Yes. Koebner phenomenon can occur for lots of other reasons, including overexposure to sunlight, phototherapy (light treatment), taking medications that suppress or ‘dampen down’ the immune system, and withdrawal from methotrexate therapy – a medication that is used to treat cancer, autoimmune conditions, and occasionally, Sweet’s syndrome (Luo, 2014).

Click here to read more about Sweet’s syndrome, Koebner phenomenon, overexposure to sunlight and phototherapy.

What causes Koebner phenomenon?

We are not entirely sure what causes Koebner phenomenon. Current theories suggest that it is a phenomenon that requires both the outer layer (epidermis) and underlying or inner layer of the skin (dermis) to be injured at the same site (Luo, 2014). The production of inflammatory substances such as cytokines, and neuropeptides – small protein-like molecules used by nerve cells to communicate with each other – have also been suggested as an initial step in a process that eventually leads to Koebner phenomenon (Luo, 2014; Yamamoto and Ueki, 2013). Chemical messengers such as nerve growth factor (NGF) may play a role, but this is still being investigated.

What is pathergy?

Pathergy, sometimes referred to as skin hypersensitivity, is an exaggerated skin injury that occurs as a result of minor skin damage or irritation (Oakley, 2011). It typically occurs after minor skin damage such as a bump or bruise, or needle stick injury, e.g. having blood taken or vaccination. The injury then leads to the development of papules (pimples or small bumps) or pustules (pimples or bumps containing fluid or pus). However, a more severe injury, e.g. a surgical procedure, can sometimes result in ulceration.

In which conditions can pathergy be seen?

Pathergy is most commonly seen in those with the neutrophilic dermatosis, Behcet’s syndrome. However, it can sometimes be seen in people with other forms of neutrophilic dermatosis, e.g. Sweet’s syndrome or pyoderma gangrenosum; in those with inflammatory bowel disease; in healthy individuals (Oakley, 2011).

What causes pathergy?

Pathergy is poorly understood, but when the outer layer of the skin is damaged, this causes activation of epidermal growth factor receptor (EGF-R) (Yamamoto and Ueki, 2013). This is a protein found on the surface of cells to which a substance called epidermal growth factor (EGF) binds. This then stimulates cell growth, cell production, and differentiation, the process where a cell changes into a more specialized cell-type.

When EGF-R is activated, this in turn leads to the production of chemokines (a family of small cytokines) such as interleukin 8 (IL-8), which may play an important role in causing neutrophilic dermatosis (Yamamoto and Ueki, 2013).

Sweet’s syndrome and pathergy.

How many people with Sweet’s syndrome demonstrate pathergy?

In literature, pathergy is rarely reported in Sweet’s syndrome. It is known to occur in 8% of patients, but due to under-reporting may be more common than first thought (Ginarte and Toribio, 2011).

What kind of injury can cause skin lesions to develop in people with Sweet’s syndrome?

In people with Sweet’s syndrome who demonstrate pathergy, skin lesions have been reported to have developed as a result of:

  • Cat scratches (Cohen, 2007).
  • Something that causes irritation when it comes into contact with the skin (contact dermatitis) (Cohen, 2007; Verma et al, 2014).
  • Skin damage caused by a biopsy, having blood taken, intravenous catheter placement (a small ‘tube’ placed in vein), or vaccination.
  • Insect bites.
  • Radiotherapy (Ibid).
  • Sunburn (Cohen, 2007).
  • Surgical wound debridement (surgical removal of affected tissue) (Cohen, 2007; Kroshinsky et al, 2012; Leighton and Amirfeyz, 2015; Otero et al , 2017; Shugarman et al, 2011).
  • Food bolus injury (injury as a result of food getting stuck when you swallow). In 2016, the first case of oral pathergy affecting the mouth, tongue and pharynx was reported in a 68-year-old female patient (Klimpl et al, 2016).

What can you do to help yourself?

If you have problems with pathergy take care to avoid:

  • Sunburn.
  • Contact with irritants.
  • Scratching.
  • Ideally, surgical procedures should only be performed when the Sweet’s syndrome has settled down or is in remission. Debridement (removal of tissue, surgical or otherwise) of a lesion should be avoided.

You can also:

  • Keep your skin well moisturised to help prevent areas of dryness and irritation. Choose products that are suitable for sensitive skin.
  • Avoid harsh cleansing solutions, e.g. strong antiseptic or alcohol-based solutions, and clean your lesions with water, saline or a very mild cleansing solution.
  • Try to avoid ‘treating’ lesions with essential oils or use with caution. There is no medical evidence to show that essential oils are a safe or effective treatment, and may cause irritation.
  • Be aware of the fact that even natural herbal extracts and creams can potentially irritate the skin.
  • Do not apply red root (blood root, bloodwort) to your lesions. This is a debriding agent, and is being advocated as a treatment for Sweet’s syndrome by some alternative therapists. There is no evidence to support this claim, and it may cause new lesions to develop.
  • Avoid or be careful when using or removing anything adhesive, e.g. plasters, tapes, dressings, or temporary tattoos.
  • Be careful of anything that irritates, rubs or chafes the skin.
  • Avoid or be careful when using cosmetic or beauty treatments, or body art that could irritate or damage the skin, e.g. facial peels, rough exfoliators, leg waxing, tweezing, henna tattoos, tattoos, or piercings.

A warning about skin prick tests for food allergy.

  • Sweet’s syndrome is not caused by food allergy, and skin prick allergy tests may be unreliable in some people with Sweet’s syndrome. This is because any reaction that does occur may be pathergy rather than genuine allergic reaction. However, if the skin prick allergy test is carried out in the correct way, then this should help to rule out other kinds of reaction.

  • If someone has a skin prick allergy test and the result is positive, then wheals or hives develop in the area where the allergen, i.e. the substance that someone is allergic to, has been applied. These wheals and hives can sometimes be mistaken for Sweet’s lesions or vice versa.

Further information.

Oakley, A. (2015) Acute Febrile Neutrophilic Dermatosis. DermNet NZ (online). Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1998. Updated September 2015. Accessed 18/06/17.

Qiao, J., Wang, Y., Bai, J., Wu, Y. and Fang, H. (2015) Concurrence of Sweet’s Syndrome, Pathergy Phenomenon and Erythema Nodosum-like Lesions. Anais Brasileiros de Dermatologia, Mar-Apr;90(2):237-9 (online).


Chern, C., Royer, M. and Turnage, W. (2017) Sweet’s Syndrome Arising in a Scar. Case Reports in Dermatology, Jul;9:86–90 (online).

Cohen, P. (2007) Sweet’s syndrome – a comprehensive review of an acute febrile neutrophilic dermatosis. Orphanet, Jul 26;2:34 (online).

Ginarte, M. and Toribio, J. (2011) Sweet’s Syndrome. IntechOpen Online.

Klimpl, D., Manser. T. and Flemmer, M. (2016) Oral Pathergy in Sweet’s Syndrome Following Food Bolus Injury, Case Reports in Clinical Medicine, Apr; 5(4): 134-139 (Scientific Research – Online). Download as free PDF.

Kroshinsky, D., Alloo, A., Rothschild, B., Cummins, J., Tan, J., Montecino, R., Hoang, M., Duncan, L., Mihm, M. and Sepehr, A. (2012) Necrotizing Sweet syndrome: a new variant of neutrophilic dermatosis mimicking necrotizing fasciitis. Journal of the American Academy of Dermatology, Nov;67(5):945-54 (PubMed).

Leighton, P. and Amirfeyz, R. (2015) Sweet syndrome: a lesson in the management of the cutaneous lesions of malignancy. Journal of Surgical Case Reports, Feb 11th (online).

Luo, A. (2014) Koebner phenomenon. DermNet NZ (online). Author: Arcana Luo, Medical Student, University of Auckland, New Zealand; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, March 2014. Accessed 18/06/17.

Oakley, A. (2011) Pathergy. DermNet NZ (online). Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2011. Accessed 18/06/17.

Otero, T., Barber, S., Yeh, D. and Quraishi, S. (2017) Necrotizing Soft Tissue Infection or Sweet Syndrome: Surgery Versus No Surgery? A Case Report. A&A Case Reports. Feb 1 (PubMed).

Shugarman, I., Schmit, J., Sbicca, J. and Wirk, B. (2011) Easily Missed Extracutaneous Manifestation of Malignancy-Associated Sweet’s Syndrome: Systemic Inflammatory Response Syndrome. American Society of Clinical Oncology, Aug 20; 29(24) (online).

Verma, R., Vasudevan, B. and Mitra, D. (2014) Unusual presentation of idiopathic sweet’s syndrome in a photodistributed pattern. Indian Journal of Dermatology; 59(2): 186-189 (online).

Yamamoto, T. and Ueki, H. (2013) Koebner Phenomenon in Rheumatoid Arthritis. Journal of Genetic Syndromes and Gene Therapy, Aug; 4:173 (online).

© 2012-2017 Sweet’s Syndrome UK


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