Hematopoetic Disorders Flashcards
Explain the most common causes of polycythemia in horses.
Polycythemia - increase in circulating RBC mass (increased PCV, RBC count, and/or hemoglobin)
***Relative - dehydration or splenic contraction (95%)
Absolute - increased erythropoiesis/production (1%)
Primary - myeloproliferative disease (polycythemia Vera)
Secondary - increased circulating erythropoietin levels
chronic hypoxia
neoplasms
renal disease
Describe the clinical signs of acute and chronic anemia in horses.
Clinical signs reflect tissue hypoxia:
Pale mucous membranes
Tachycardia
Tachypnea
Lethargy / exercise intolerance
Weakness
Systolic heart murmur
Scleral blood vessels not visible
Acute (blood loss or acute severe hemolysis):
Anxious
Sweat profusely
Tachycardia
Chronic:
Lethargy
Weakness
Exercise intolerance
Causes of regenerative vs nonregenerative anemia
Regenerative:
- hemorrhage
- hemolysis
Nonregenerative:
- anemia of chronic disease
- bone marrow failure
- chronic kidney disease - kidneys produce erythropoietin, which signals bone marrow to make RBCs
- iron deficiency
Develop a treatment plan for a horse with acute, severe hemorrhage.
- Stop the hemorrhage
- Volume replacement: hypertonic saline followed by isotonic IV fluids
- Maintain oxygen carrying capacity: blood transfusion
Explain the clinical signs and clinicopathologic findings that would enable you to differentiate between intravascular and extravascular hemolysis in a horse.
Both
Hyperbilirubinemia
Normal plasma protein
Intravascular
Hemoglobinemia (pink plasma)
Hemoglobinuria
Describe two diagnostic tests that might confirm a diagnosis of immune-mediated anemia in horses.
DX of IMHA
1. autoagglutination - a result of antibodies on RBCs; distinguished from rouleaux when diluted with saline as rouleaux will disperse
- Coombs test - tests for antibodies on RBCs
In horses, IMHA is usually secondary to drugs, neoplasia, bacterial/viral infections
Describe the difference between immune-mediated disease and auto-immune disease.
Auto-immune disease is primary IMHA, a true autoimmune process where antibodies to red blood cells are produced.
Immune mediated disease - antibodies or immune complexes are absorbed into RBC membranes secondary to another cause (in horses - bacterial/viral infections, neoplasia/esp lymphosarcoma, or drugs/esp penicillin).
Prepare a treatment plan for a horse with immune-mediated anemia secondary to a bacterial infection.
Discontinue current medications
Treat underlying bacterial infection
Corticosteroids may worsen a primary infectious process - use once cleared
Blood transfusion if necessary
Diurese if intravascular (hemoglobinemia/hemoglobinuria present)
Describe two diagnostic tests that might confirm oxidative damage as a cause of hemolysis.
Explain the pathophysiologic processes that underlie the observed abnormalities.
Oxidative injury to RBCs following ingestion of toxin such as dried and senescent red maple leaves ->
Blood smear: Heinz body formation - oxidized hemoglobin
Methemoglobinemia - oxidized iron
Explain to an owner why iron deficiency anemia is so uncommon in adult horses and under what circumstances it might occur.
Iron deficiency anemia is extremely rare in horses since they have constant access to dirt, which has high iron content, as do legumes. Iron deficiency only develops when the rate of iron loss from the body exceeds the absorption of iron from the diet. Foals in hospital (on flooring) more susceptible as milk is a poor source of iron.
Can occur with chronic blood loss:
- chronic GI hemorrhage -> NSAID toxicosis, neoplasia, severe gastroduodenal ulcers, gastric squamous cell carcinoma
- coagulopathies
- severe internal/external parasitism
Choose an iron supplement that is safe and effective when administered IV to horses.
Choose an iron supplement that is safe and effective when administered PO to horses.
Iron cacodylate IV
Ferrous sulfate PO - 2mg/kg
ICIV
FSPO
List the causes of nonregenerative anemia in horses and indicate the most common.
Nonregenerative anemia - failure to replace senescent RBCs as they are removed from circulation
Iron deficiency - extremely uncommon in adult horses
*Anemia of chronic disease - VERY COMMON
Bone marrow suppression - rare; usually results in pancytopenia
Anemia secondary to other organ dysfunction (endocrine, hepatic, renal - decreased erythropoietin)
Explain to an owner how Equine Infectious Anemia virus is transmitted.
Transmitted primarily by the intermittent feeding of biting horseflies and deer flies, or iatrogenically by use of contaminated needles, surgical instruments, dental floats, etc. Infected horses remain infected for life. There is no vaccine available to prevent EIA in horses.
Develop a plan for a boarding stable to prevent equine infectious anemia in their horses.
- Require negative Coggins as part of every PPE, all new horses, and all events involving congregation of horses
- Test all horses at the stable yearly
- Encourage rigorous fly control
- Thoroughly disinfect any items contacting equine blood prior to use on another horse
- NEVER use the same needle for injections in different horses
Summarize the similarities and differences between the two parasitic organisms that can cause equine piroplasmosis.
Both
- Caused by intra-RBC hemoprotozoan parasites
- Infection spread by ixodid tick vectors
- can also be transmitted iatrogenically via blood contaminated instruments, multiple use needles, or blood doping
- infected horses may show few/no clinical signs
Babesia caballi
- horses may eliminate infection w/o treatment
- horse and primary tick vector, Dermatocentor nitens, serve as reservoirs
Theileria equi
- remain persistently infected for life
- persistently infected horse is reservoir
- thought to result in more severe clinical signs
