Page 1427 - Small Animal Internal Medicine, 6th Edition

CHAPTER 87 Disorders of Hemostasis 1399

injury. As a consequence, vWD is usually characterized by Other Congenital Platelet Function Defects
primary hemostatic defects (e.g., petechiae, ecchymoses, Platelet function defects leading to spontaneous primary
VetBooks.ir mucosal bleeding). However, most dogs with vWD do not hemostatic bleeding have been reported in at least three
breeds of dogs (Otterhounds, Foxhounds, and Basset
bleed spontaneously but bleed excessively during or after
surgery; excessive bleeding during teething or estrus can also
malities are similar to those seen in dogs with vWD, but the
occur, but petechiae and ecchymoses are rare. Most dogs Hounds). The clinical signs and clinicopathologic abnor-
with vWD and spontaneous bleeding seen at our clinic are vWF concentrations are normal or high. A syndrome of
brought in for the evaluation of diffuse oropharyngeal or spontaneous and postoperative bleeding resembling Scott
vaginal bleeding. People with vWD can also have low circu- syndrome in humans from a lack of platelet procoagulant
lating concentrations of factor VIII, leading to spontaneous activity has been well characterized in German Shepherd
secondary hemostatic bleeding (i.e., the clinical findings of Dogs (Jandrey et al., 2012).
hemophilia A); however, this is extremely rare in dogs. Peri-
natal death, abortions, or stillbirths are common in litters
with vWD. SECONDARY HEMOSTATIC DEFECTS
The hemostasis screen results and platelet counts are
normal in most dogs with vWD. However, the results of a Dogs with secondary hemostatic defects are usually evalu-
PFA-100 test or BMBT usually assist in establishing a diag- ated because of collapse, exercise intolerance, dyspnea,
nosis. As a general rule, the PFA-100 closure time or BMBT abdominal distention, lameness, subcutaneous bruising, or
is prolonged if the vWF concentration or activity is low. The masses. The collapse and exercise intolerance are usually
BMBT may be the most cost-effective method for screen- caused by anemia resulting from intracavitary bleeding,
ing dogs for vWD, although its results are not foolproof. It as are the dyspnea and abdominal distention. The lame-
can be done before surgery in breeds at risk or if the owner ness is usually caused by hemarthrosis, and the masses or
or breeder is interested in determining whether the dog is lumps usually represent hematomas. Cats and dogs with
likely to have this disorder. However, a normal bleeding time secondary hemostatic disorders do not have petechiae or
does not necessarily rule out vWD. At our clinic we rou- ecchymoses, or mucosal bleeding (e.g., melena, epistaxis)
tinely use the PFA-100 before surgery in dogs at high risk is rarely seen. In general, the severity of the bleeding
for vWD so that appropriate therapy can be instituted before is directly related to the severity of the deficiency of the
or during surgery. A diagnosis of vWD can be confirmed by clotting factor(s). Liver disease and rodenticide poisoning
quantifying vWF in specialized veterinary coagulation labo- leading to vitamin K deficiency are the two most common
ratories. Genetic testing for vWD in specific breeds is avail- causes of secondary hemostatic defects seen at our clinic;
able through commercial diagnostic laboratories (VetGen; however, the former is rarely associated with spontaneous
https://www.vetgen.com/canine-vWD1.html). bleeding. As noted, these disorders are more common in
Most dogs with type 1 vWD can be successfully treated dogs than in cats and are far less common than primary
before surgery or during a bleeding episode with desmopres- hemostatic defects.
sin acetate (DDAVP), which causes a massive release of vWF
from the endothelial cells and results in shortening of the CONGENITAL CLOTTING
BMBT and the PFA-100 closure times within 30 minutes of FACTOR DEFICIENCIES
administration. A single 1-µg/kg dose of DDAVP (intrana- Congenital clotting factor deficiencies, as well as the breeds
sal preparation) given subcutaneously consistently lessens affected, are listed in Box 87.3. They are relatively common
bleeding in dogs with type 1 vWD despite modest increases in dogs but are rare in cats. Most genetic mutations leading
in vWF concentration. DDAVP is not effective in dogs with to these defects have been well characterized, and some labo-
types 2 or 3 vWD because these dogs have an abnormal ratories now offer genetic testing for congenital coagulopa-
(i.e., nonfunctional) vWF or lack vWF. Cryoprecipitate is thies. Hemophilia A and B are sex-linked traits; the modes
the blood component of choice for dogs with vWD; a unit of inheritance of other coagulopathies vary. In affected
of cryoprecipitate is defined as the volume obtained from animals, the severity of the bleeding is usually inversely pro-
a unit of FFP (see Chapter 82). We use a dosage of 1 U portional to the concentration of the individual clotting
cryoprecipitate/10 kg of body weight; therefore a Dober- factor affected (e.g., bleeding is more severe in association
man Pinscher typically receives 3 U. If cryoprecipitate is not with a very low factor activity). Clinical signs usually include
available, FFP or WFB can be used. DDAVP can also be spontaneous hematoma formation, which the owners may
administered to the blood donor dog 1 hour before blood describe as lumps, and bleeding into body cavities, as well as
is collected to maximize the yield of vWF. Systemic prohe- signs compatible with so-called fading puppy syndrome and
mostatic agents such as aminocaproic or tranexamic acids, protracted umbilical cord bleeding after birth. Abortions or
and Yunnan baiyao can also be used in these patients. The stillbirths in the litter are common. Petechiae and ecchymo-
use of topical hemostatic agents such as fibrin, collagen, or ses are not present in dogs with congenital clotting factor
methacrylate is also indicated to control the local bleeding. deficiencies. Cats with congenital clotting factor deficiency
As is the case in dogs with other inheritable disorders, dogs usually do not bleed spontaneously but have intraoperative
with congenital vWD should not be bred. or delayed postoperative bleeding.