Asymptomatic Macrothrombocytopenia in a Young Pure-Bred Beagle Dog: A Case Report

• Published in: Toxicologic pathology 2011-10, Vol.39 (6), p.980-987
• Main Authors: Bodié, Karen, Gagne, Gerard D., Sramek, Mary K., Desmond, David J., Abel, Stephen J., Fagerland, Jane A.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blood Platelets - cytology; Blood Platelets - ultrastructure; Borrelia burgdorferi; Borrelia burgdorferi - isolation & purification; Dogs; Ehrlichia canis; Ehrlichia canis - isolation & purification; Erythrocytes - metabolism; Genotype; Glucocorticoids - metabolism; Male; Medical sciences; Microscopy, Electron, Transmission; Platelet Count; Prednisone - therapeutic use; Rickettsia rickettsii; Rickettsia rickettsii - isolation & purification; Thrombocytopenia - diagnosis; Thrombocytopenia - physiopathology; Toxicology
• ISSN: 0192-6233; 1533-1601
• DOI: 10.1177/0192623311416261

During baseline evaluation prior to a preclinical safety study, a 10-month-old male pure-bred Beagle dog was found to have marked thrombocytopenia (6 × 103 platelets [PLT]/µL) associated with a mean platelet volume (MPV) of 17.9 fL. Tests for Rickettsia rickettsii, Ehrlichia canis, and Borrelia burgdorferi were negative. Buccal bleeding time was normal. Over 3 months, PLT were 4 to 141 × 103 PLT/µL, and MPV was 11.4 to 25.1 fL; however, PLT were 16 fL during most of this period. Antinuclear antibody (ANA) and anti-PLT antibody tests were negative. Genotyping for the presence of a beta 1-tubulin mutation demonstrated the normal wild-type gene. Treatment with prednisone resulted in normal values after only 3 days. Ultrastructure of enlarged PLT was consistent with that of immature PLT, characterized by reduced numbers of peripheral microtubules and the presence of rough endoplasmic reticulum, free ribosomes, Golgi apparatus, and a prominent canalicular system. PLT ultrastructure and glucocorticoid responsiveness supported a diagnosis of immune-mediated thrombocytopenia that was masked by the cyclic nature of PLT decreases and lack of clinical signs. Inclusion of such a dog in a preclinical safety study could result in misinterpretation of clinical pathology findings.