Lisa Gordon
Animal Health Laboratory, University of Guelph, Guelph, ON.
AHL Newsletter 2024;28(4):10.
A three-month-old Holstein heifer calf presented for generalized skin masses and increased respiratory effort of a few days’ duration. On examination, the calf was tachypneic and tachycardic with a temperature of 40.2˚C, and harsh lung sounds on thoracic auscultation. Peripheral lymph nodes were markedly enlarged (Fig. 1). In-house CBC showed markedly elevated lymphocytes, and euthanasia was performed due to poor prognosis. Postmortem examination revealed enlargement of internal lymph nodes and the formation of adhesions between abdominal viscera. A comprehensive suite of tissues was submitted for histopathology at the Animal Health Laboratory. The eighteen examined lymph node samples were effaced by monomorphic sheets of large neoplastic lymphocytes. Neoplastic lymphocytes were disseminated throughout the viscera, and were present within the spleen, liver, kidney, lung, heart, uterus, ovary, intestines, bladder, and abomasum (Fig. 2). The calf was diagnosed with disseminated large cell lymphoma, characteristic of juvenile lymphoma, also known as calf lymphoma.
Bovine lymphoma can be categorized based on factors such as age of onset, affected tissues, association with bovine leukemia virus (BLV), and the frequency of occurrence (sporadic vs. endemic/enzootic within a population). Juvenile lymphoma is a rare, sporadic form of bovine lymphoma that typically affects cattle younger than 6 months of age, usually between 3 to 6 months, although cases have been reported in cattle ranging from 1 month to 3 years old. This form of lymphoma is considered spontaneous and is not linked to enzootic bovine leukosis (EBL) or BLV infection. Other types of sporadic lymphoma in cattle include thymic lymphoma, which primarily affects cattle between 6 months and 2 years, and cutaneous lymphoma, which generally affects cattle between 1 to 3 years of age. These forms of lymphoma are all non-infectious and non-contagious, and typically only individual animals within a population are affected. On the other hand, enzootic bovine leucosis is not sporadic, is associated with BLV infection, and generally affects cattle greater than 2 years of age. While EBL is characterized by a B-cell lymphoma, the sporadic lymphomas (juvenile, thymic and cutaneous) can originate from either B- or T-cell populations.
Clinically, young calves with juvenile lymphoma often present with generalized lymphadenopathy, while older calves may exhibit weakness, weight loss, and depression. Enlarged lymph nodes are typically smooth, firm, and non-painful on palpation. Additional clinical signs may include dyspnea, tachypnea, harsh lung sounds, tachycardia, and pallor. Some calves may also have fever, ruminal tympany, hepatomegaly, ataxia, and diarrhea. A complete blood count often reveals anemia and leukocytosis due to lymphocytosis. Bone marrow examination shows an increased myeloid-to-erythroid ratio and neoplastic lymphocyte proliferation. Neoplastic lymphocytes are found in lymph nodes and in various visceral organs, including the liver, spleen, pancreas, heart, uterus, and occasionally the thymus. However, the thymus is less frequently involved and less infiltrated by neoplastic lymphocytes compared to primary thymic lymphomas. The prognosis for juvenile lymphoma is grave, with affected calves typically succumbing to the disease within 2 to 8 weeks of the onset of clinical signs.
Figure 1. Markedly enlarged prescapular lymph node. Photo credit: Dr. Meggy Chan.
Figure 2. Histologic sections of tissues infiltrated by neoplastic lymphocytes. H&E stain. 2A. Lymph node. Neoplastic lymphocytes efface the normal architecture (asterisk). 2B. Liver. Subcapsular (thin arrow) and periportal (thick arrow) neoplastic lymphocytes. 2C. Uterus. Perivascular neoplastic lymphocytes (thin arrow). 2D. Ovary. Stromal neoplastic lymphocytes (thin arrow).
References
1. Angelos, JA. Proliferative disorders of the myeloid and lymphoid systems. In: Large Animal Internal Medicine. 6th ed. Smith BP, Van Metre DC and Pusterla N, eds. Elsevier, 2020;1180-1181.
2 Harbo SJ, et al. Characterization of lymphocyte populations by flow cytometry in a calf with sporadic juvenile lymphoma. Vet Clin Path 2004;33(3):163–167.