IMHA Flashcards
IMHA
- Life threatening
- Common in dogs and rare in cats
- Characterised by type II immune reaction where RBCs coated with immunoglobulin, complement or both are removed from circulation bu direct destruction or phagocytosis
Primary IMHA
- Idiopathic
- autoimmune hemolytic anemia
- true autoimmune reaction against self antigen on erythrocytes
Secondary IMHA
- associated with presence of a foreign antigen
- stimulates immune system to destroy erythrocytes without a true autoantibody
- triggers: systemic infections, drugs and neoplasia
- more common than primary in cats
- non immune mediated : direct RBC destruction from disorders such as Dirofilaria immitis infection and vena-caval syndrome (hemolysis occur due to trauma to the RBCs when they circulate through parasite thrombus)
What kind of dogs and cats are predisposed to IMHA?
Female dogs and male cats
Average age of 6.5years for dogs and 3 years for cats
Signs and symptoms of IMHA
*Lethargy, depression, anorexia for 3 days or more, discoloured urine, vomiting, diarrhoea, dyspnea,
Seasonal component to IMHA
Spring and summer
Initial physical exam findings
Pallor, tachycardia, fever, icterus, cranial organomegaly, lymphadenopathy, petechiae
Cats: hypothermic
Systolic heart murmur, hyper dynamic pulse quality, dyspnea, collapse
PCV in IMHA patient
Less than 25% and as low as 6%
Spherocytosis common in 85-95% of cases (difficult to identify in cats due to size)
Signs of regeneration
Polychromasia, anisocytosis, macrocytosis, nucleated RBCs, reticulocytes
Nonregenerative anaemia
- found in up to 50% of dogs and most cats at presentation
* dogs take 3-5 days while cats take 7 days to regenerate
Thrombocytopenia
*occur in 50-70% of dogs and rare in cats
Combination of thrombocytopenia and hemolytic anaemia
Evan’s syndrome
Serum biochemical adnormalities
Total bilirunin elevation, hepatic transaminase and alkaline phosphatase elevation, azotemia, and hyperglobulinemia.
Urinalysis shows bilirubinuria or hemoglobinuria
DIC
Prolonged coagulation times (prothrombin time, activated partial thromboplastin time) and increased fibrin degradation products and d-dimers are consistent with DIC
What test is used to diagnose IMHA?
Spontaneous macroagglutination on slide agglutination test is diagnostic when rouleaux formation has been ruled out by saline washing
- Not all dogs will hav autoagglutination
- Macroagglutination is not diagnostic of IMHA in cats
How is slide agglutination test performed ?
- one drop of EDTA-blood on a glass slide and gently mixing with one drop of saline
- slide is gently rocked while being observed for clumping of RBCs (macroagglutination)
Coomb’s test
- direct antiglobulin test (DAT)
- used to detect anti-erythrocyte antibody or complement on the surface of RBCs
- Mixing of anticoagulated patient RBCs with rabbit or goat anti-canine (or anti-feline) immunoglobulin or complement which reacts with immunoglobulin or complement-coated RBC to result in aglgutination
- positive in 35-60% of dogs with IMHA
- can produce false positive and negative results
Treatment for IMHA
- no single best treatment
- supportive care to treat anemia - IVF crystalloids
- minimise risk of secondary complications
- immunosuppresive drug therapy - Glucocorticoids: prednisolone PO, dex IV if PO not tolerated
- potentially secondary immunosuppressive drugs: azathioprine and cyclosporine
- potential blood transfusion: packed RBCs over whole blood
- less volume
- less chance of reaction to plasma proteins
What is the risk of IV catherization in patients with IMHA?
It increases the risk of pulmonary thromboembolism
-the most common cause of death for dogs with IMHA
How do you determine when to transfuse an IMHA patient?
Based on presence of clinical signs of weakness, tachycardia, tachypnea, rapidly decreasing PCV
Drawbacks of transfusion therapy
- suppression of erythropoietin response
- prolongation of time to erythroid recovery
- possibly increased risk of pulmonary thromboembolism
- presence of autoantibodies may shorten survival of transfused red cells
Complications of IMHA
- Thromboembolism
- indicative of patient in hypercoagulable state
- risk factors for development of thrombophilia and thromboembolism
- blood stasis
- hypercoagulability
- vascular endothelial injury
- hyperbilirubinemia
- hypoalbuminemia
- severe thrombocytopenia
Where is the most common location of clinically evident thromboembolism?
The pulmonary system
-cerebral thromboembolism can also occur
Clinical signs of thromboembolism in the pulmonary system?
Acute respiratory difficulty Orthopnea Profound anorexia Acute neurologic decompensation Neuro-lateralizing signs Sudden death
What anticoagulant therapy can you use to treat suspected hypercoagulability associated with IMHA?
Heparin require antithrombin to be effective and antithrombin is decreased in dogs with IMHA- hence not an effective anticoagulant
