Page 1426 - Small Animal Internal Medicine, 6th Edition

1398 PART XIII Hematology

TABLE 87.4
VetBooks.ir Classification of von Willebrand Disease in Dogs

TYPE
BREEDS
DEFECT
1 Low concentration of Airedale, Akita, Bernese Mountain dog, Dachshund, Doberman Pinscher, German
normal vWF Shepherd, Golden Retriever, Greyhound, Irish Wolfhound, Kerry Blue Terrier, Manchester
Terrier, Miniature Pinscher, Papillon, Pembroke Welsh Corgi, Poodles, Schnauzer, other
pure breeds and mixed-breed dogs
2 Low concentration of German Shorthaired Pointer, German Wirehaired Pointer
abnormal vWF
3 Absence of vWF Familial: Dutch Kooiker, Scottish Terrier, Shetland Sheepdog
Sporadic: Dutch Kooiker, Scottish Terrier, Shetland Sheepdog; sporadic cases Border
Collie, Chesapeake Bay Retriever, Cocker Spaniel, Eskimo dog, Labrador Retriever,
Maltese, Pitbull, mixed breeds

vWD, von Willebrand disease; vWF, von Willebrand factor.
Modified from Brooks MB, Catalfamo JL: Von Willebrand disease. In Weiss DJ, Wardrop KJ, editors: Schalm’s veterinary hematology, ed 6,
Ames, Iowa, 2010, Wiley-Blackwell, p 612.

an otherwise healthy animal, or the animal has a family Endothelium/
GP Ib
history of bleeding or pronounced bleeding during a pre- GP IIb/IIIa collagen
vious surgery. Congenital platelet dysfunction syndromes (vWF
are rare, with the notable exception of vWD. Some authors receptor)
classify vWD among the congenital clotting factor deficien-
cies; however, because its clinical manifestations are those vWF
of a primary hemostatic defect, I include it in this section. Platelet
Acquired platelet function disorders are more common;
clinically they are mainly secondary to monoclonal gam-
mopathies, ehrlichiosis, uremia, retroviral infections, or F VIII:C
drug therapy.
von Willebrand Disease
vWD is the most common inherited bleeding disorder in
humans and dogs but is rare in cats. The term von Willebrand FIG 87.4
Interaction between vWF, platelet, and subendothelial
syndrome (vWS) is reserved for an acquired vWF deficiency. surfaces. F VIII:C, Factor VIII coagulant; GP, glycoprotein;
vWD can be classified into three types (Table 87.4). Dogs vWF, von Willebrand factor.
with the disease typically have a decreased concentration or
activity (type 1 vWD), absence of circulating vWF (type 3
vWD), or low to normal concentrations of an abnormal vWF vWD and hypothyroidism in dogs. Type 2 vWS has been
(type 2 vWD), which result in mild (if any) spontaneous reported in dogs with aortic valvular disease; in those dogs,
bleeding or, more likely, prolonged surgical bleeding. In dogs the high shear associated with turbulent flow across the valve
vWD can be inherited as an autosomal dominant trait with resulted in selective depletion of high-molecular-weight
incomplete penetrance or, more rarely, an autosomal reces- vWF multimers (Tarnow et al., 2005).
sive trait (see later). This disorder has been reported to occur In humans vWF is produced by megakaryocytes and
in more than 50 breeds of dogs but is more common in endothelial cells, circulates in plasma complexed to factor
Doberman Pinschers, German Shepherd Dogs, Poodles, VIII coagulant (factor VIII C), and is one of the major adhe-
Golden Retrievers, and Shetland Sheepdogs. In these breeds sive proteins in the body. In the dog, platelets do not con-
the defect is inherited as an autosomal dominant trait with tribute as much vWF to plasma as in humans. vWF is mainly
incomplete penetrance. In Scottish Terriers and Shetland responsible for causing platelets to adhere to the subendo-
Sheepdogs, it can be inherited as an autosomal recessive thelial structures (e.g., collagen) in areas of high shear once
trait; homozygous dogs have no detectable vWF concentra- endothelial cell damage has occurred, thus initiating the for-
tions and are usually severely affected. Type 1 vWD has been mation of the primary hemostatic plug (Fig. 87.4). The vWF
purportedly reported to occur in association with clinical molecule circulates coiled; it uncoils at the site of endothelial
hypothyroidism in dogs; however, most scientifically con- damage, binds to the subendothelium and then to the plate-
trolled studies have failed to prove an association between let receptors, and the platelets are reeled in to the site of