PERIVASCULAR DERMATITIS
This idiopathic entity affects the paws of dogs and usually is a localized or focal lesion. Clinicially it resembles interdigital furunculosis but without the furunculosis or pyoderma component. It is a perivascular dermatitis with fibrosis and lymphocytes and plasma cells around vessels.
This is an rare diagnosis. Clinically, the dogs have wheals and erythema that is most noticeable on glabrous skin. Histological lesions are in the dermis only – the epidermis is usually normal but can have a cell poor cytotoxic interface pattern. There is varying degrees of dermal edema. Capillaries throughout the dermis, particularly in the mid-dermis have hypertrophied endothelial cells. Cellularity is usually minimal and can be neutrophils and eosinophils and macrophages. There is no vasculitis.
It is normally an hypersensitivity / allergic reaction that could be a food adverse reaction.
Urticaria and angioedema is about pure massive edema. Urticaria is edema of the dermis. Angioedema has edema of the subcutis too. There is no inflammation.
Dogs develop a rare disease of the skin that is nodular and neutrophilic. Affected dogs have multiple nodules in their skin, but can have extracutaneous disease including oral only disease, and arthritis. Some dogs have fever and neutrophilia.
The histological lesions are perivascular to diffuse and nodular. They are dominated by neutrophils, but may have eosinophils too. Vascular injury is considered to be secondary to metabolites from neutrophils. Veins are often involved because of this.
Differential diagnoses include Sterile pustular erythroderma of Dachshunds, infectious neutrophilic disease, and canine eosinophilic dermatitis
Bradley CW, Cain CL, Wong TS, Ferracone JD, Goldschmidt KH, Mauldin EA. Discriminatory features of acute eosinophilic dermatitis with oedema (Wells-like syndrome) and sterile neutrophilic dermatosis (Sweet's-like syndrome) in dogs. Vet Dermatol. 2019; 30: 517-e157.
Johnson CS, May ER, Myers RK, Hostetter JM. Extracutaneous neutrophilic inflammation in a dog with lesions resembling Sweet's Syndrome. Vet Dermatol. 2009 Jun;20(3):200-5. doi: 10.1111/j.1365-3164.2009.00746.x. Epub 2009 Apr 16. Erratum in: Vet Dermatol. 2010 Apr;21(2):232. PMID: 19392767.