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Author: James Cameron, medical student, University of Auckland, Auckland, New Zealand. DermNet New Zealand Editor in Chief: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy editor: Gus Mitchell/Maria McGivern, July 2017.
Fogo selvagem is most prevalent in rural areas of the southern and midwestern states of Brazil, such as Goiás, Mato Grosso do Sul, Paraná, São Paulo, and Minas Gerais. Cases have also been reported in Tunisia, Peru, Paraguay, El Salvador and Colombia. It most commonly affects children and young adults.
Fogo selvagem is closely linked with poverty and malnutrition and has a higher incidence in areas near rivers and streams. Fogo selvagem is associated with the human leukocyte antigen complex (HLA), indicating a genetic predisposition to the disease.
Fogo selvagem is an autoimmune disease in which an individual's immune system reacts against the keratinocytes and desmosomes that make up the skin.
In reaction to fogo selvagem, the body produces immunoglobulin G4 (IgG4) antibodies that bind to the desmosomal protein desmoglein-1 (Dsg1). This causes the surface keratinocytes of the epidermis to detach from each other and fill with fluid, causing the characteristic blisters.
The exact pathogenesis of fogo selvagem is not known, but a combination of genetic and environmental factors are thought to be involved. Expression of HLA-DRB1-0404, 1402 or 1406 alleles is found in patients with fogo selvagem, suggesting a genetic susceptibility. It is hypothesised that a salivary protein from a blood-sucking insect like the black fly (Simulium nigrimanum) triggers the autoimmune response as black fly bites have been found to be more common in patients with fogo selvagem.
The classic lesions of fogo selvagem are superficial blisters or vesicles that progress over weeks to months. Its features include:
If untreated, complications may include:
These complications are less likely to occur if the disease is treated immediately.
The diagnosis of fogo selvagem is based on both the local prevalence of the disease and its characteristic blisters and a positive Nikolsky sign (where gently rubbing affected skin causes a blister to form).
Skin biopsy shows acantholysis of the upper epidermis, often resulting in a subcorneal cleft (where a loss of adhesion between keratinocytes creates leads to the skin layer splitting). The subcorneal cleft increases in size and can detach, with or without bulla formation. Other histological findings can include papillomatosis, hyperkeratosis and parakeratosis. Mild lymphocytic infiltration may be present.
Direct immunofluorescence demonstrates epidermal intercellular fluorescence — mainly anti-IgG or anti-C3 autoantibodies.
An ELISA (rDsg1-His) test can be used to detect intercellular fogo selvagem autoantibodies.
Other skin conditions may be under consideration in a patient with superficial blistering of the scalp, face, neck and upper trunk such as:
For generalised blistering, consider:
With adequate treatment, the prognosis of fogo selvagem is good with no long-term sequelae.
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