Immune-mediated hemolytic anemia (IMHA) Flashcards
What is the pathomechanism of IMHA
IMHA involves the destruction of RBC by a “Type II” (antibody-dependent cytotoxic) immune reaction
The immune reaction may be targeted against:
- normal erythrocytes that have been antigenically altered (e.g., by an antigenic epitope supplied by an infectious agent such as M. haemofelis or a drug that is attached to the cell surface)
- an alloantibody binding to a bloood group antigen (e.g., transfusion reactions or neonatal isoerythrolysis)
Can you give some examples of causes associated with secondary IMHA in cats
Secondary IMHA has been associated with:
- a variety of infectious agents (e.g., hemotropic mycoplasmas, FIP, FIV, Hepatozoon)
- neoplasia (e.g., lymphoma, erythroid leukemia, mastocytosis)
- inflammatory conditions (e.g., abscesses, pyothorax, pancreatitis)
What is the prevalence of primary IMHA in cats
Primary IMHA in cats may be more common than once thought
Majority of cases are younger than 3 years
What could you say about cold agglutinin disease
Cold aggglutinin disease is a very rare immune disease characterized by the presence of high concentration sof cold sensitive antibodies in the peripheral circulation
- these are usually IgM autoantibodies that are active only at cold temperatures and directed against red blood cells, causing them to agglutinate
It seems to be very rare in adult cats
It seems to occur more commonly in kittens with neonatal isoerythrolysis, where the face and ears are spared, but tail-tip necrosis is occasionally reported in kittens that survive the acute hemolytic crisis
How is the diagnosis of IMHA done
IMHA may be detected via the observation of gross auto-agglutination on a “saline-slide” test or a positive Coomb’s test
- neither of these tests are able to differentiate between primary and secondary IMHA
- they are useful for differentiating immune-mediated versus non-immune-mediated causes of anemia
What is the principe of the Coomb’s test and how is it done
The Coomb’s test detects antibody and/or complement on the surface of RBCs
- it is equivalent to visible auto-agglutination on the saline slide test
The test is based on the addition of species-specific antibodies (Coomb’s reagent) to the washed RBCs of the patient
- agglutination of the RBCs gives a positive result
The Coomb’s reagents may be polyvalent or monovalent
The sensitivity of test may be enhanced by performing it at several dilutions, at both 4°C and 37°C to detect both cold and warm agglutinins
The possibility of false positive and false negative results should be borne in mind
Could you list what is important to remember when attempting to diagnose IMHA in cats
Macroscopic slide agglutination is typically positive
Spherocytes are rare, but ghost cells maybe seen
Evidence of hemolysis may be present
- hemoglobinemia
- +/- hemoglobinuria
- +/- bilirubinemia in the absence of cholestasis
Absence of other causes of RBC destruction/hemorrhage
Positive Coombs
- a negative Coombs makes IMHA unlikely, but a positive Coombs doesn’t confirm IMHA
Evidence of response to immunosuppressive treatment
What is the treatment for IMHA
Treatment for secondary IMHA should be aimed at the underlying disorder
Supportive measures such as fluid therapy and blood transfusions should be used as necessary
Stress should also be kept to a minimum (e.g., gentle nursing, quiet environment)
Specific therapy for IMHA
- prednisolone is the initial therapy of choice (2-4 mg/kg, PO, q24h or divided if GIT irritation present)
- dexamethasone can be administered at 0.25-1 mg/kg every 24 hours parenterally, if oral medication is contraindicated
- once the PCV has stabilized in the low normal range for at least a weak, the dose of prednisolone can be tapered, usually by reducing by 1/4 to 1/2 every 2-4 weeks
Which risk could threaten the anemic patient receiving fluid therapy or blood transfusion
It can be very easy to volume overload these patients, as it is only the red blood cells that are reduced
Close monitoring of patients using daily body weights and resting breathing rates will help to identify pleural effusion (most common), pulmonary edema or ascites in patient that develop volume overload
Which alternative drugs can be added to prednisolone if necessary
Chlorambucil or cyclosporin can be added to the treatment if the animal requires very high doses of prednisolone to maintain remission or has a comorbidity (e.g., diabetes mellitus, cardiac disease) that mandates that the dose of glucocorticoids be kept at a minimum
Mycophenolate mofetil has also been used
What is the prognosis for IMHA
Generally, the prognosis for cats with primary IMHA is more favorable compared to dogs
- cats tend not to suffer complications such as pulmonary thromboembolism
- most cats with primary IMHA should be in remission within 4 weeks of starting treatment
- relapse appears to occur in approximately 40% of cats but remission can be achieved again
Cats with secondary IMHA have a more guarded prognosis, which is dependent on the underlying disease process
