Thromboembolism in a Bitch - Diagnosis by Infrared Thermography

Background: Thermography is a noninvasive, non-contact, painless, and non-ionizing imaging technique that records cutaneous thermal patterns generated by infrared emission of the surface. The surface heat is closely related to dermal microcirculation. Thromboembolism is responsible for important changes in the thermal pattern of the body surface due to physical obstruction of blood flow, being the main complication in immune-mediated hemolytic anemia. The aim of this paper is to report a dog with thrombus in his left forelimb secondary to idiopathic hemolytic anemia, whose diagnostic screening was performed through infrared thermography. Case: A 9-year-old mixed breed bitch was referred to a veterinary hospital with a history of emesis, diarrhea and dark-colored urine for 2 days. The complete blood count showed hypochromic macrocytic anemia (hematocrit [HTC] 28%, reference: 37 to 55%) with the presence of nucleated erythrocyte (14/100 leukocytes, reference: 0 to 5/100 leukocytes), polychromasia and spherocytes. Leukocytosis (28,300 mm(3), reference: 6,000 to 17,000 mm(3)) by neutrophilia with left deviation and toxic granulations was also present, in addition to hemoglobinuria at urine exam. Therefore, treatment for immune-mediated hemolytic anemia (IMHA) was instituted. After 2 days, the animal returned with acute functional impairment of the left forelimb. Physical examination revealed that the limb was cold, without pulse, proprioception, reflexes, and deep pain. New blood analyses revealed decreased hematocrit (HTC 17%, reference: 37 to 55%), and increased total leukocyte number (57,000 mm3, reference: 6,000 to 17,000 mm(3)). Infrared thermography revealed an important temperature difference between the limbs, with the affected limb temperature considerably lower (31.3 degrees C) when compared to the contralateral limb (35.0 degrees C). Thermography showed the site of the thrombus in the medial portion of the limb (cephalic vein), where the catheter had been placed for fluid therapy. Due to the severity of the condition, the bitch was submitted to amputation surgery, which occurred without complications. The patient had a good response to treatment, with decreased signs of hemolysis and hypercoagulability. The medications were slowly withdrawn, and the clinical discharge occurred after 4 weeks. Discussion: In humans, thermography has been widely used in the assessment of thrombotic diseases, contributing to diagnosis, localization, and prognosis. In veterinary medicine, however, the use of this tool in the diagnosis of thromboembolism is still rare. The difference of 3.7 degrees C between the affected and contralateral limb was objectively verified using thermography. A minimum difference of 2.4 degrees C between limbs has high sensitivity and specificity for diagnosing thromboembolism and occurs due to the reduction in local blood flow. In the present case this tool was essential for the anatomical location of the thrombus, which was in the middle third of the forearm, and allowed an adequate surgical planning. It is known that the main complication of IMHA is thromboembolism. Its predisposing factors include venous stasis, endothelial damage, and hypercoagulability, being exacerbated by cage confinement, decubitus and presence of a peripheral venous catheter. The reported case corroborates at least one of these factors since it had a peripheral venous catheter in the left forelimb, which later showed absence of pulse, spinal reflexes, pain and proprioception. The thermography showed to be an objective, rapid and non-invasive tool to diagnose and precisely locate the thrombus, which allowed for adequate treatment and surgical planning for the case. To the best of our knowledge, this is the first report about use of thermography to diagnose thromboembolism secondary to immune-mediated hemolytic anemia in a dog.