Thrombosis of the Pulmonary Artery in a Yearling Thoroughbred Colt

Abstract

A 1-year-old thoroughbred colt was examined at the University Veterinary Hospital (University College Dublin) for pyrexia of unknown origin. The colt had a 6-week history of recurrent fever (38.9-40.6 1C), weight loss, and intermittent shifting lameness that had involved various limbs before presentation at the hospital. Two weeks before referral, a blood sample taken by the referring veterinarian had disclosed anemia and leukocytosis, and serum had tested negative for equine infectious anemia with an ELISA test. No improvement in clinical signs had been noted after treatment with neomycin penicillin (IM) and enrofloxacin (IV) of unknown dose and duration. Some resolution in clinical signs after therapy by procaine penicillin (IM), gentamicin (IV), and phenylbutazone (PO) of unknown dose and duration was seen, but clinical signs later worsened and the colt was referred for additional evaluation and treatment.Upon examination, the animal was in poor body condition (body condition score, 3/9) 1 and appeared depressed. The colt's rectal temperature (38.3 1C) and respiratory rate (14 breaths/min) were within the normal range and moderate tachycardia (60 beats/min) was present. No cardiac murmurs or arrhythmias were detected upon auscultation and lung sounds were normal during a rebreathing examination. A large painful soft tissue swelling was noted over the right carpus. No other clinically relevant abnormalities were detected on physical examination.Hematologic examination identified mild anemia (packed cell volume [PCV], 28%; reference range, 36-52%; red blood cells, 7.65 Â 10 6 /mL; reference range, 7-11 Â 10 6 /mL; hemoglobin, 9.1 g/dL; reference range, 13.8-19.4 g/dL), leukocytosis (34,500/mL; reference range, 5,500/mL-9,200/mL) with neutrophilia (27,260/ mL; reference range, 2,000/mL-6,000/mL) and left shift (band neutrophils, 3,450/mL; reference range, 0/mL-100/ mL), monocytosis (1,040/mL; reference range, 0/mL-500/ mL), and hyperfibrinogenemia (700 mg/dL; reference range, 100-400 mg/dL). Serum biochemistry revealed hyperproteinemia (9.8 g/dL; reference range, 5.7-7.9 g/dL) with hyperglobulinemia (7.4 g/dL; reference range, 2.4-4.8 g/dL), and hypoalbuminemia (2.4 g/dL; reference range, 2.9-3.7 g/dL), decreased albumin to globulin ratio (0.32; reference range, 0.62-1.46 2 ), decreased serum creatinine concentration (94 mmol/L; reference range, 100-170 mmol/L) and increased alkaline phosphatase activity (358 IU/L; reference range, 0-100 IU/L).Based on the history, physical examination, and laboratory findings, differential diagnoses for fever of unknown origin included a source of persistent infection or inflammation, such as an upper respiratory tract infection (eg, guttural pouch empyema, sinusitis, pharyngeal abscess), lower respiratory tract disease (eg, bronchopneumonia, pleuropneumonia, abscess, neoplasia), abdominal disease (eg, peritonitis, abscess, neoplasia), bacterial endocarditis, piroplasmosis, and diseases currently not reported in Ireland including equine viral arteritis (EVA), anaplasmosis, and l...