Page 1041 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1016 CHAPTER 9

VetBooks.ir haemoglobinuria is usually present. Diagnostic test- treatment can be discontinued. If the underlying
disease cannot be identified or effectively treated,
ing to identify an underlying cause is important.
Primary IMHA is typically identified by exclusion of
ticularly poor if lymphoma is present. The severity
known causes of secondary IMHA. the prognosis is poor to grave. The prognosis is par-
of haemolysis and the presence of additional organ
Management damage determines the outcome.
Treatment of the underlying disease (if identified)
and discontinuation of ongoing drug therapy are RED MAPLE LEAF TOXICOSIS
critical. If drug treatment is required, the specific
drug should be changed if possible. If the anaemia Definition/overview
is severe, supportive therapy in the form of blood The dried leaves of the red maple tree (Acer rubrum)
transfusion may be required (see Table 9.2). (Fig. 9.18), if consumed in sufficient quantity, can
Immunosuppressive drugs are used to minimise cause Heinz body haemolytic anaemia. As such, horses
further antibody formation. Corticosteroids (dexa- often become ill in the autumn when leaves drop onto
methasone 0.05–0.2 mg/kg i/v or i/m q12–24 h, pastures where animals are grazing. The quantity of
tapering based on response to treatment) are most leaves necessary to incite haemolysis is variable and
commonly used. Azathioprine (3 mg/kg p/o q24 h) depends on the individual horse and the amount of the
may be useful in refractory cases. The initial goal is toxic compound in the leaves in a given season.
to stabilise the PCV within 24–48 hours. Intravenous
fluid therapy with a balanced electrolyte solution Aetiology/pathophysiology
may be useful in reducing the risk of haemoglobin- Dried red maple leaves contain an undetermined
associated renal damage. Severely anaemic animals toxic compound that causes oxidative damage to
may benefit from intranasal oxygen therapy. Exercise RBCs. Leaves eaten directly from a tree or freshly
should be restricted until haemolysis has ceased and fallen leaves do not produce a similar outcome.
the PCV has returned to normal. The toxin causes rapid depletion of glutathione,
producing oxidative damage to RBCs and subse-
Prognosis quent Heinz body formation. Haemolysis is primar-
The prognosis is good if the underlying problem ily intravascular. Methaemoglobinaemia may also
can be identified and addressed. The best progno- develop when oxidation of haemoglobin iron to a
sis is with drug-associated IMHA, provided that non-oxygen-carrying state occurs.

Clinical presentation
Clinical presentation can be highly variable, rang-
9.18 ing from acute death to gradual development of
disease. Weakness, lethargy, anorexia, pale mucous
membranes and icterus or cyanosis are common.
Cyanosis may not develop if anaemia is severe. Urine
is frequently red-tinged due to haemoglobinuria.

Differential diagnosis
Other causes of Heinz body haemolytic anaemia
including onion ingestion, phenothiazine toxicosis,
and lymphoma should be considered.

Diagnosis
A history of exposure to dried red maple leaves and
Fig. 9.18 Red maple (Acer rubrum). (Photo courtesy clinical signs of acute onset of anaemia are sug-
Jeff Dean ©) gestive. The pasture should be examined for the