Equine Health Update February 2017 Issue | Page 31

EQUINE | CPD

EQUINE | CPD

Equine Lymphoma - An Update

By Dr Rick Last – BVSc ; M . Med . Vet ( Pathology )
Specialist Veterinary Pathologist Vetdiagnostix – Veterinary Pathology Services
Introduction

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Lymphoma although rare in horses is still considered the most common hematopoietic neoplasia arising from lymphoid tissue ( lymphnodes , spleen , gut-associated lymphoid tissue , bone marrow ) of this species . Leukemia is a neoplasia arising from cells of the bone marrow with lymphocytic leukemia ( bone marrow lymphoma ) being one of the leukocytic leukemias . The overall incidence of lymphoma is 1.3-2.8 % of all equine tumor ’ s . Horses of any age can be affected , but most reported cases are in horses 4-10 years of age . There appears to be a breed predisposition in Quarter Horses , Thoroughbreds and Standardbreds .
Classification
Equine lymphoma can be classified into multicentric , alimentary , mediastinal , cutaneous and solitary tumours of extra-nodal sites . Common clinical signs in the horse include weight loss , depression , lethargy , ventral oedema , recurrent fever and lymphadenopathy . Hematology and serum biochemistries are usually non-specific , but lymphoma should be further investigated if anemia , hyperfibrinogenaemia , hyperproteinaemia and hypoalbuminaemia are reported without any clear indication of infectious disease . In most instances the diagnosis of lymphoma is only made late in the course of the disease , due to the insidious nature of the disease and lack of pathognomonic signs in this species . Due to most diagnoses being made late in the progression of the disease the prognosis is poor in most instances .
Multicentric Lymphoma
Multicentric lymphoma is considered the most common form of lymphoma in the equine species and is characterized by widespread asymmetrical involvement of peripheral and / or internal nodes and various visceral sites . Involvement of internal lymph nodes however is variable . Liver , spleen , intestine , kidney and bone marrow are the most commonly documented visceral sites , although they have also been reported in upper airways , central nervous system , heart , adrenal glands , reproductive organs and eye . Leukemia is observed in cases with bone marrow involvement .
Clinical presentation of multicentric lymphoma is very variable depending on which visceral organs are involved . The majority of horses with multicentric lymphoma however do exhibit weight loss , ventral oedema , pyrexia , increased respiration , rapid pulse and lymphadenopathy . Other less common clinical presentations with this form of lymphoma include abdominal distention , icterus , malabsorption , hematuria , polydipsia / polyuria , neurological signs , ocular signs , pseudohyperparathyroidism and alopecia .
Alimentary lymphoma
The alimentary form of lymphoma accounts for approximately 19 % of lymphoma cases in horses . Equine intestinal lymphoma may affect multiple segments of the intestinal tract ( more common in horses < 10 years
• Volume 19 no 1 • February 2017 • 31