Image Quiz: Dermatology-A dog with a suddenly crusty, itchy muzzle

Canine eosinophilic furunculosis of the face is correct!

This condition is thought to be a hypersensitivity reaction, primarily to flying, venomous insects such as wasps or bees, although some cases have been seen in the winter and may be related to spider bites. Lesions may also occur on the pinnae and, occasionally, on the trunk, legs, or ventrum. The onset is acute and often peaks at 24 hours after the sting.

Cytologic examination usually reveals many eosinophils with or without neutrophils and bacteria. A skin biopsy can confirm the diagnosis, and histologic examination reveals an eosinophilic mural and luminal folliculitis and furunculosis with lesser numbers of macrophages, neutrophils, and lymphocytes.

This condition is rapidly responsive to prednisone (1 to 2 mg/kg) given orally once a day until the lesions resolve (usually five to 10 days) and then on an every-other-day basis for another 10 to 14 days. The prognosis is excellent.