This dog was presented with an acute purpura.
After ruling out bleeding disorders a biopsy was taken and indicated vasculitis. 
Cutaneous vasculitis is an uncommon immune-mediated
inflammatory disease of the blood vessels. Aberrant immune
response leads to inflammation and necrosis of blood vessels.

 Possible causes in veterinary patients are an underlying
infection caused by a virus, bacteria (e.g. Bartonella species),
fungus, protozoa (e.g. Leishmania species2), or rickettsial
disease; food hypersensitivity; malignancy; drug reaction (e.g.
meloxicam, human albumin); rabies vaccination; metabolic
disease; systemic lupus erythematosus; and cold agglutinin
disease. The disease may also be idiopathic.