Page 1057 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1032 CHAPTER 9

VetBooks.ir 9.35 tumours in the horse, and must be differentiated
from the more common lymphoma, which can have
associated tumour cells in circulation.

Aetiology/pathophysiology
The underlying cause of lymphocytic leukaemia is
unknown.

Clinical presentation
Clinical signs tend to be vague and non-specific and
can include weight loss, poor appetite, weakness,
lethargy, oedema, colic, petechial haemorrhage,
fever and lymphadenopathy. ALL tends to occur in
younger horses.
Fig. 9.35 Bone marrow aspirate from a horse
with lymphocytic leukaemia. There is a monotypic Differential diagnosis
population of neoplastic lymphocytes present. Normal The main differentials include other haematopoietic
haematopoietic tissue is absent due to complete tumours, particularly lymphoma, which can have
effacement by neoplastic cells (Wright’s stain). circulating tumour cells.

developing haematopoietic cells. Further characteri- Diagnosis
sation of the cell type of origin can be difficult based The diagnosis of leukaemia is based on observation
on morphology alone in AML. Cytochemistry can of atypical cells on blood smears and bone mar-
be attempted, but results can be difficult to interpret. row with ALL (Fig. 9.35) or increased numbers of
The increased availability of cell lineage-specific small lymphocytes with CLL. Cytopenia of other
markers for individual species will result in a better cell lines (erythrocytes, neutrophils, platelets) is
ability to characterise these rare tumours in horses variable, but is more likely with ALL. Bone mar-
using immunohistochemical and flow-cytometric row examination typically reveals hypercellularity
techniques. and increased proportion of blast cells (>20%) for
ALL. Flow cytometry can be used to determine
Management/prognosis B- or T-cell origin, although markers for both
The prognosis for AML is poor to grave in horses. phenotypes can be present for a given tumour.
The prognosis for MPNs and MDS are unknown, Infiltration of other organs frequently occurs,
as these are very poorly documented tumours in including lymph nodes, liver, spleen, lungs, kid-
this species. The uncommon occurrence of these neys and GI tract.
diseases has resulted in little study and therapeu-
tic investigation. Chemotherapeutic options for Management
large animals tend to be very expensive and are No treatment is effective for ALL and most horses
unproven. die or are euthanased soon after diagnosis. CLL is
a rare disease, and information on treatment is dif-
LYMPHOPROLIFERATIVE DISEASE ficult to find.
(LYMPHOCYTIC LEUKAEMIA)
Prognosis
Definition/overview The prognosis for a horse with either ALL or
Neoplastic proliferation of immature (acute lympho- CLL is poor to grave. Most are euthanased or die
cytic leukaemia, ALL) or mature (chronic lympho- within days to weeks of diagnosis, with occasional
cytic leukaemia, CLL) lymphocytes. These are rare exceptions.