Type 3 von Willebrand’s disease in a Shetland sheepdog

Abstract

A 3.75-year-old, spayed female, Shetland sheepdog was presented with excessive bleeding from a gingival surface. The dog’s condition deteriorated over 24 h and whole fresh blood was transfused. Type 3 von Willebrand’s disease was diagnosed. Coagulation was achieved and the dog was released with recommendations for a sedentary lifestyle and careful monitoring.

A 3.75-year-old, spayed female, Shetland sheepdog, was presented (day 1) with a history of bleeding from the mouth after eating a bone, 3 d previously. There was no known history of consumption of a vitamin K antagonist. Prolonged bleeding had been reported previously following removal of deciduous teeth but not in association with an ovariohysterectomy. The owner reported several uninvestigated episodes of bloody vomit and diarrhea over the previous several years.

On examination, the dog was quiet, alert, tachycardic (145 bpm), and panting. The dog’s ruff was blood stained. The oral mucous membranes were pale and the capillary refill time (CRT) was < 1 s. Blood was oozing from the gingiva, caudal to the incisors, but no wound or petechiae were noted, and the gums appeared otherwise healthy. No other abnormal findings were evident on physical examination. Hematocrit was 27 × 10² L/L (reference range, 37 to 55 × 10² L/L). Blood was collected into 3.8% sodium citrate at a ratio of 9 parts blood to 1 part anticoagulant, and the sample was submitted (Vita-Tech Canada, Markham, Ontario) for a platelet count and a coagulation panel that included prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time, and fibrinogen count. A freshly thawed plasma transfusion was declined by the owner and the dog was treated with vitamin K (K1 Injectable; Vétoquinol, Levaltrie, Quebec), 5 mg/kg bodyweight (BW), SC, to be continued at 2.5 mg/kg BW, PO, q12h, pending results of the coagulation panel. The owners declined hospitalization for further monitoring and the dog was released.

On the morning of day 2, the dog was presented with continued bleeding; it also appeared to be more lethargic. The oral mucous membranes were paler and the CRT was < 2 s. The dog was tachycardic (152 bpm) and panting. A grade II/VI heart murmur was auscultated. A complete blood (cell) count (CBC) (QBC VetAutoread Hematology Analyzer; IDEXX Laboratories, Westbrook, Maine, USA) revealed severe regenerative anemia, with a hematocrit of 12.4 × 10² L/L, reticulocytes 2.1% (reference range, 0% to 1.5%), mild leukocytosis (22.3 × 10⁹ cells/L; reference range, 6.0 to 16.9 × 10⁹ cells/L), neutrophilia (20.9 × 10⁹ cells/L; reference range, 3.3 to 12.0 × 10⁹ cells/L), and thrombocytopenia (114 × 10⁹ cells/L; reference range, 175 to 500 × 10⁹ cells/L). No spherocytes or nucleated red blood cells were observed on a blood smear. Blood was drawn into a citrated tube and submitted for assay of von Willebrand factor antigen (vWF:Ag).

Due to the severity of the anemia, the dog was transfused with 260 mL of whole fresh blood from a donor dog, mixed with 120 mL of 0.9% NaCl. Less than 2 h after transfusion began, the gums appeared pinker and the gingival bleeding had stopped. Three hours after transfusion, the heart rate had decreased to 128 bpm and the respiratory rate was 60 bpm.

The coagulation report revealed all parameters within normal limits, including a platelet count of 243 × 10⁹ cells/L. On day 3, vital signs were within normal limits, hematocrit was 40 × 10² L/L, and the gums were pink. The dog was discharged with recommendation that she be carefully monitored for recurrence of bleeding episodes manifested as epistaxis, gingival hemorrhage, hematuria, or gastrointestinal bleeding evidenced by melena. Leash-only exercise and a relatively sedentary lifestyle were also recommended.

The results of the vWF:Ag assay were reported on day 10 as 0% vWF:Ag (normal range 70% to 180%, borderline range 50% to 69%, carrier range 1% to 49%), indicating that the dog was a homozygote for inherited von Willebrand disease (vWD).

On the basis of the breed and clinical presentation of gingival hemorrhage, a tentative diagnosis of vWD had been made. This diagnosis was supported by the normal platelet count and the results of the coagulation panel, and confirmed by the routine vWF:Ag assay.

Most Shetland sheepdogs with vWD are affected with a form of vWD analogous with type 1 vWD in humans; that is, the vWF structure is normal, but the plasma concentration is low vWF (1). In one study, there was a 23% vWD gene prevalence in 6000 Shetland sheepdogs screened for vWD (2). Absence of vWF, as demonstrated in this dog, is classified as type 3 vWD. Type 3 vWD in the Shetland sheepdog is believed to be associated with either homozygosity for the vWD gene or, more probably, double heterozygosity. These dogs, which are severely affected clinically, are most likely to be the offspring of heterozygous parents affected with type 1 vWD (2). In other breeds with a high prevalence of type 1 vWD, such as Doberman pinschers, homozygosity is thought to be lethal, since dogs affected with type 3 vWD have not been reported. Possible explanations for the survival of Shetland sheepdogs with severe type 3 vWD include their smaller size and resultant decrease in weight bearing stresses, double heterozygosity rather than homozygosity, or another unknown factor (2). Type 2 vWD, characterized by selective depletion of high-molecular weight multimers, apparently does not occur in Shetland sheepdogs (2).

The initial differential diagnosis for the coagulopathy in this case included vWD; a platelet disorder, such as thrombocytopenia or a thrombocytopathy; a congenital coagulation deficiency, such as hemophilia A or B; vitamin K antagonist poisoning; or, less likely, a vessel wall defect. To arrive at a definitive diagnosis, several diagnostic tests had to be employed, in combination with a careful review of the case history and presenting clinical signs.

Evaluation and differentiation of coagulopathies requires a basic understanding of the process of hemostasis. Hemostasis is divided into 3 stages. Primary hemostasis consists of vascular constriction, in combination with platelet adhesion and aggregation. Secondary hemostasis involves stabilization of the platelet plug with fibrin produced through the coagulation cascade. Tertiary hemostasis is a fibrinolytic process that acts to prevent excessive platelet-fibrin plug formation (3). In the first stage, following damage to the endothelial cells lining blood vessels, vWF is adsorbed to the subendothelial collagen and platelet cells and plays an important role in platelet adhesion to the exposed subendothelial collagen, especially in the microvasculature (5). Along with fibrinogen and other adhesive proteins, vWF plays an additional role in platelet-platelet aggregation by bridging receptors on adjacent platelets (4).

The presenting clinical signs in this case, including bleeding after removal of deciduous teeth, gingival bleeding, hematemesis, and bloody diarrhea, are typical of vWD. Common clinical problems reported in affected dogs include bleeding from sites of minor injury and venipuncture, prolonged estrus, and bleeding from mucosal surfaces, including the nasal cavity, gastrointestinal mucosa, and gingiva (2).

Laboratory evaluation of vWD can be accomplished by using quantitative or qualitative assays (5). As in this case, vWD in the dog usually results from an absolute deficiency of vWF in the blood, but occasionally it may be due to a reduction in the functional activity of vWF (6). Measurement of vWF:Ag in plasma is usually accomplished by electroimmunoassay (EIA) (Laurell immunoassay) or enzyme-linked immunosorbent assay (ELISA), assay) using antibodies directed against antigens present on the vWF molecule. Patient results are compared with results of assays on pooled plasma from normal dogs and are reported as a vWF percentage or vWF units/dL. The concentration of vWF in pooled plasma is considered 100% or 1 unit/mL, while the absolute concentration of vWF in normal canine plasma is approximately 6 μg/mL (4). The ELISA technique employed in this case, which has become the preferred method of analysis, has several advantages over EIA, including increased sensitivity, efficiency, and ability to test larger numbers of samples (4).

Qualitative methods give an indication of the relative amounts of different sized multimers within the sample and are used to classify the subtype of vWD in a patient (5). Multimeric analysis is not used routinely in screening animals for vWD, but it is employed in research laboratories to better characterize the disease (6). Normal vWF is a multimer, which may be large, intermediate, or small in size, depending on the number of polymerized subunits. Normal dogs carry all 3 types. Though functionality of the multimers increases with size, antigenicity decreases. von Willebrand’s disease may result from ity a predominance of the less functional small multimers. The clinical severity of this type of vWD can be under-estimated when only antigenic detection methods, such as EIA or ELISA, are employed (6). The proportion of variously sized vWF multimers may be estimated by using crossed immunoelectrophoresis or multimeric analysis with sodium dodecyl sulfate-agarose eletrophoresis, which may also identify the microheterogenicity of individual multimers (5). Since no vWF was detectable in this case, the use of multimeric analysis was not relevant.

Functional platelet agglutination assays, which estimate the activity of vWF in a sample by measuring in vitro agglutination of platelets with a cofactor, such as botrocetin, were not employed in this case (5).

The hemostatic competency of an individual with vWD is best determined by assessing bleeding time (5). Laboratory tests can quantify and qualify vWF levels, but they do not always accurately represent hemostatic ability. Bleeding time refers to the duration of hemor-rhage from a small standardized wound involving only microscopic blood vessels (5). It is a useful presurgical screening test for breeds with known increased prevalence of vWD (7), which includes the Shetland sheepdog. Bleeding times are prolonged in vWD, but they may also be increased in association with other disorders of primary hemostasis (5).

Plasma vWF circulates as a complex with factor VIII. In contrast to the disease in humans, in which marked secondary decreases in factor VIII coagulant activity may occur with vWD, factor VIII levels in vWD dogs seldom drop more than 20%, and as a result, APTT times in affected dogs are usually normal, as in this case, or only slightly prolonged (5).

Veterinarians and breeders should be aware of the potential for Shetland sheepdogs to be carriers of the vWF gene or to be clinically affected with vWD. The risk for increased bleeding should be kept in mind when elective and medical procedures are undertaken in this breed. Breeders should screen dogs for vWD and refrain from breeding carriers to avoid producing progeny severely clinically affected with type 3 vWD.