Page 1040 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

H aemolymphatic system 1015

VetBooks.ir Aetiology/pathophysiology brown to dark red from haemoglobinuria. There
may be a history of recent illness, drug treatment or
Destruction of RBCs occurs because antigen–
antibody complexes on the surface of the cells are
recognised as foreign by the immune system and lymphadenopathy.
are removed from circulation. This can be due to Differential diagnosis
loss of tolerance of a self-antigen, unmasking of an Other causes of haemolytic anaemia, including
existing antigen or the presence of a new antigenic Heinz body-induced haemolysis and parasitic hae-
molecule. Complement-mediated cell lysis can also molysis, should be considered.
occur in some instances. IMHA has been reported
as a sequela to lymphoma in horses. Infectious causes Diagnosis
include EIA and acute viral and bacterial infections. Diagnosis is based on suggestive clinical signs and
Drugs, particularly penicillins, cephalosporins laboratory evidence of haemolysis, including poten-
and sulphonamides, have also been associated with tially severe anaemia that increasingly becomes
IMHA. macrocytic, hypochromic with anisocytosis and
Haemolysis can occur extravascularly (i.e. in mac- an increasing RDW. Agglutination may be present
rophages in the spleen, liver and/or bone marrow) grossly and/or microscopically (Figs. 9.16, 9.17).
or intravascularly. Extravascular haemolysis results RBC ghosts may be observed on the blood smear
in increased unconjugated bilirubin and, eventually, if intravascular haemolysis is present. Spherocytes
conjugated bilirubin, resulting in clinical icterus. may be present but are difficult to detect in horses.
Intravascular haemolysis as a primary mechanism Haemoglobinaemia and haemoglobinuria may also
causes haemoglobinaemia and haemoglobinuria. be present. The direct antiglobulin (Coombs) test
There may be cases where both types of haemolysis is often positive. The most consistent finding on a
exist concurrently. serum biochemical profile is an increase in unconju-
gated bilirubin; conjugated bilirubin is often concur-
Clinical presentation rently elevated to a lesser degree. Elevations in urea
Horses present as weak and with pale and/or icteric and creatinine will be present if pigment- associated
mucous membranes. Tachycardia and tachypnoea renal failure has developed. Hypoxic damage to
may be present, depending on the severity and rapid- the liver may result in elevations in hepatocellu-
ity of onset of anaemia. Urine may be discoloured lar enzyme activity. Macroscopic or microscopic

9.16 9.17

Fig. 9.16 Grossly visible
agglutination of red blood Fig. 9.17 Blood smear with an arrow indicating
cells. (Photo courtesy RBCs in a large grape-like cluster indicative of
RM Jacobs) microagglutination (Wright’s stain).