Page 1058 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

H aemolymphatic system 1033

VetBooks.ir LYMPH NODE DISEASES

Clinical presentation
LYMPHOMA
Horses are often presented because of weight loss,
Definition/overview lethargy and enlarged lymph nodes (Fig. 9.36). Other
Lymphoma is characterised by infiltration of solid features may include dyspnoea, colic and neurological
tissues with neoplastic lymphocytes. Lymphoma has and ocular signs, depending on the localisation of the
several clinical manifestations in the horse. Only tumour. Splenic enlargement or internal masses may
rarely does lymphoma become leukaemic, with neo- be palpable p/r. Horses with the cutaneous form have
plastic cells found in circulating blood. This tends a few to many firm nodules scattered over the body,
to be observed in horses with generalised or mul- sometimes with peripheral lymph node involvement.
ticentric lymphoma. Other forms include cutane- The intestinal form has been associated with the devel-
ous, mediastinal and intestinal disease. Unlike many opment of IMHA and so horses may be presented for
other types of neoplasia, lymphoma is not uncom- weakness, icterus and pale mucous membranes.
mon in young horses and may even occur in foals.
Differential diagnosis
Aetiology/pathophysiology The potentially heterogeneous morphological
Unregulated proliferation of a cell line at a certain stage appearance of equine lymphoma means that it must
of development results in an increased proportion of be carefully differentiated from lymphocytic hyper-
these cells in haemolymphatic tissues. The infiltra- plasia, which is characterised by an increased pro-
tive nature of the tumour may result in replacement portion of non-neoplastic immature cells.
of normal cells, which will create distortion of normal
architecture. Neoplastic cells are rarely observed in Diagnosis
circulation. Tissues most commonly affected include Diagnosis is confirmed by observing a predomi-
the lymph nodes, spleen and liver. nance of neoplastic lymphocytes altering the normal
architecture of a solid tissue on fine-needle aspira-
tion or excisional biopsy (Fig. 9.37). The subtype of
9.36

9.37

Fig. 9.37 Lymph node fine-needle aspirate from
a horse with lymphoma. There is a heterogeneous
population of small, medium and large
lymphocytes; however, the arrows indicate medium to
Fig. 9.36 Enlarged submandibular lymph nodes in a large lymphocytes with atypical morphology (multiple
horse with lymphoma. prominent nucleoli) (Wright’s stain).