Von Willebrand Disease in a Thoroughbred Mare and Foal

Abstract

A n 8-year-old pregnant Thoroughbred broodmare presented for continuous right unilateral epistaxis of 2 days duration. The mare had self-limiting intermittent episodes of hemorrhage including epistaxis and 1 instance of bleeding for 3 days from a Caslick's procedure. No abnormalities were detected by a CBC or serum biochemical analysis. Coagulation times (prothrombin time [PT] and activated partial thromboplastin time [APTT]) and a platelet count were within the reference range. A standard bleeding time test performed on the left palmar aspect of the carpus, just above the accessory carpal bone, with a template-bleeding device, 1,a revealed a prolonged bleeding time (17 minutes , reference range 6-12 minutes). The mare had prolonged bleeding from venipuncture sites. Endoscopic examination of the upper airway and guttural pouches did not reveal a focal source of the blood, which seemed to be seeping from the mucosa of the nasal turbinate bones. Ra-diographs of the skull did not reveal any abnormalities other than an increased opacity in the maxillary sinus, consistent with a hematoma. The epistaxis persisted for 5 days despite empirical treatment with vitamin K 1 (500 mg SC q24h) and aminocaproic acid (Amicar, b 20 g in 10 L of lactated Ringer's solution IV q12h for 2 treatments). The hematocrit was 24% on day 5 of hospitalization and the mare was given 4 L of fresh plasma intravenously. The epistaxis stopped shortly after the administration of the plasma. The mare was discharged from the hospital 2 days later. The mare delivered a live foal without complications 5 months after discharge. The mare was reexamined 20 months later for epistaxis from the right nostril of 2 days duration. Physical examination showed the mare to be bright and alert with continuous dripping hemorrhage from the right nostril. Endo-scopic examination revealed multifocal hemorrhage from small vessels at caudal aspect of the turbinates. No evidence was found of a tumor or traumatic injury. The mare had no history of the administration of aspirin or other nonsteroidal anti-inflammatory drugs. Radiographs of the head did not reveal any abnormality. Examination of clinicopathologic data indicated a mild normocytic, normochromic anemia (PCV, 31%; reference range, 33-48%) and a low plasma protein concentration (5.1 g/dL; reference range, 5.4-6.6 g/ dL). The platelet count was within the reference range (197 10 3 /L). A serum chemistry panel and electrolytes were all within the reference ranges. The PT was normal but the APTT was slightly high (patient, 68 seconds; control, 55 seconds; reference range, 40-60 seconds). The bleeding time was greater than 25 minutes. The mare was treated with 4 L of fresh plasma intravenously and the bleeding stopped 4 hours later. Blood was collected in citrate tubes