Heinz Body Hemolytic Anemia
Johanna L. Watson • Gary P. Carlson • Monica Aleman
Definition and Etiology
Acute hemolytic anemia can develop following exposure to a variety of oxidizing agents. These include chemicals such as phenothiazine, methylene blue, acetylphenylhydrazine, or plants like wild or domestic onions, members of the Brassica family (rape or kale), and wilted or dried leaves of the red maple (Acer rubrum).1-7 Red maple toxicosis (RMT) has been reported in horses, zebras, and alpacas.5,8-10 Heinz body hemolytic anemia also occurs in sheep on specially formulated diets that are low in molybdenum, which results in chronic copper toxicity; as herd problems in cattle grazing rye grass (Secale cereale)1 or selenium-deficient pastures in Florida12; and in association with selenium deficiency as a contributing factor in postparturient hemoglobinuria in cattle in New Zealand.13 These agents produce or allow oxidative denaturation of hemoglobin and resultant aggregation of the protein globin, which appears as Heinz body inclusions within the red blood cells.
Heinz body anemia has been seen in association with lymphoma in a horse and was possibly due to failure of the reticuloendothelial system to remove Heinz bodies, as has been reported in horses with EIA.14Clinical Signs and Differential Diagnosis
Clinical signs vary with the species involved, specific toxin or toxic metabolites, amount of toxin ingested, time course of the disease process, and occurrence of complicating secondary factors like hemoglobin nephrosis and acute renal failure. Weakness, lethargy, anorexia, and exercise intolerance are the usual presenting complaints, and death losses can occur. Mucous membranes are generally pale with variable to marked icterus. Heart and respiratory rates are generally elevated, but rectal temperature is usually within normal limits.
Horses with RMT may be subclinical or may present with lethargy, muddy or cyanotic mucous membranes, tachycardia, inappetence, weakness, colic, icterus, brown discoloration of the blood, and pigmenturia. Rarely, sudden death occurs.10 Most horses develop clinical RMT during summer and fall, and the high mortality rate may relate to the combination of a rapidly progressive hemolytic anemia and formation of methemoglobin. Urine output may be reduced, and the presence of hemoglobin, methemoglobin, or bilirubin may make urine appear dark.It is not possible to differentiate Heinz body hemolytic anemia from other potential causes of hemolytic anemia without laboratory evaluation. The absence of fever may help differentiate these anemias from infectious causes of hemolytic anemia. History of exposure to potential oxidizing agents and the fact that these toxic plants may produce death losses or clinical signs in multiple animals at the same time should help differentiate these cases from autoimmune hemolytic anemia.
Clinical Pathology
Poisoning or intoxication resulting in Heinz body formation usually causes acute and profound anemia. In the early stages a high percentage of erythrocytes may have Heinz body inclusions. Later, as these cells are removed from the circulation and replaced by young cells from the bone marrow, the relative number of affected cells may decrease markedly. Heinz bodies are round, oval to serrated, refractile granules usually located near the cell margin or protruding from the cell. They are best visualized with vital stains like crystal violet or new methylene blue applied to unfixed blood smears. Heinz bodies appear as bluish-green inclusions with new methylene blue stain. Fixing blood smears with methanol in preparation for staining with the classic Wright stain interferes with stain uptake, and Heinz bodies appear as a pale area within or projecting from the cell margin and can easily be missed. After the first 3 or 4 days the anemia is usually associated with hematologic evidence of an active erythrogenic response in all species except the horse.
Total plasma protein usually remains within normal limits, and the Coombs test is negative. Red maple poisoning also results in depletion of red cell mass, reduced glutathione, methemoglobinemia, increased osmotic fragility, and modest elevations of liver-derived serum enzyme activities.Rapid and profound erythrocyte destruction may lead to hemoglobinemia and hemoglobinuria. Development of renal failure secondary to hemoglobin nephrosis is a definite risk in these animals and is reflected by modest to marked increases in the blood urea nitrogen and creatinine, as well as changes in the urinalysis.6,7 These parameters should be monitored in severely affected animals. As with other causes of hemolytic anemia, serum bilirubin, particularly indirect-reacting bilirubin, is elevated.
The clinicopathologic abnormalities of horses with RMT include anemia (PCV as low as 7.5%), eccentrocytes, Heinz bodies, and elevated plasma methemoglobin concentration.10 Other significant findings are an inflammatory leukogram and renal insufficiency (75% and 40% of cases, respectively).10 Mild serum total bilirubin elevation is observed in most cases, and hemoglobinuria is seen in all affected patients.
Pathophysiology
Heinz bodies are formed by precipitation of oxidatively denatured hemoglobin. The hemoglobin contained within the red blood cell is constantly undergoing mild oxidative stress associated with oxygen transport, as well as generation of superoxide radicals and hydrogen peroxide within the cell. There are a number of reducing mechanisms within the red cell to counteract these oxidative processes through production of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) and reduced glutathione. The occurrence of Heinz body hemolytic anemia could be viewed as a consequence of exposure to oxidative stresses that simply overwhelmed the cells' reductive capacity. Selenium deficiency results in a decrease in glutathione peroxidase, a selenium-containing enzyme, and selenium deficiency may in special circumstances contribute to Heinz body formation by impeding the ability of the cells to respond to oxidative stress.
There are substantial species variations in the rate of Heinz body formation that relate to the chemical structure of hemoglobin and efficacy of erythrocyte-reducing mechanisms in the face of oxidative stress.1 Red cells with Heinz bodies are less deformable than normal cells and are rapidly removed from the circulation by the reticuloendothelial system in the spleen, where they are phagocytized and broken down. Splenectomy or corticosteroid therapy may alter Heinz body clearance mechanisms, allowing significant numbers of affected red cells to remain in the circulation of otherwise normal animals.Gallic acid is a strong oxidant present in red maple leaves and has been implicated in the oxidation of hemoglobin, methemoglobin formation, and Heinz body anemia.5,6,15 Methemoglobin results from the oxidative change of hemoglobin iron to the nonfunctional ferric state (see discussion of nitrate poisoning in Chapter 54). This is normally prevented by glutathione reductase, ascorbic acid, and reduced glutathione. Methemoglobin cannot load or transport oxygen and, when present in sufficient quantities, results in a brown color of peripheral blood and mucous membranes. An estimation of methemoglobin concentration in a blood sample can be made by comparing the hemoglobin concentration measured by the cyanmethemoglobin method, which measures all forms of hemoglobin, and the oxyhemoglobin method, which only measures oxyhemoglobin but not other forms (e.g., methemoglobin). Methemoglobinemia and hemolytic anemia have been reported in a mare and her dam in association with decreased levels of red cell glutathione and glutathione reductase, presumably as a result of an inherited enzymatic defect.16
Treatment
Treatment is largely a matter of removal from the source of toxicity and provision of supportive care. Blood transfusion can be beneficial in severely anemic patients, particularly when there is insufficient evidence of active erythropoietic response.
Iron-containing hematinics are of little benefit. IV fluid therapy is indicated in animals with hemoglobinuria or azotemia to reduce the potential for further renal damage. High doses of vitamin C (ascorbic acid, 50 to 100 g IV daily), together with fluids and transfusion, were thought to aid recovery in two horses with red maple poisoning.17 Another report suggests that vitamin C therapy may have little impact on survival of affected horses, and when methylene blue was used to treat the associated methemoglobinemia in two horses, both died.18 Therapeutic goals should be to improve tissue oxygenation and perfusion and control inflammation and pain (e.g., with NSAIDs). Horses treated with corticosteroids have an increased likelihood of death.10Prognosis
Prognosis in animals with modest anemia and evidence of response is good if the inciting factor can be controlled or eliminated. The mortality rate of experimental and naturally occurring cases of RMT in horses is said to be 60% to 65%.18 In animals with rapidly progressive and profound anemia, prognosis is poor unless blood transfusion is undertaken. Complications are associated with hypoxia, hypoperfusion, and inflammation. Horses may develop acute renal failure, colic, pyrexia, and laminitis. A retrospective study of 32 horses reported a fatality rate of 59% but failed to show an association between mortality and severity of anemia.10
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