Immune Mediated Haemolytic Anaemia (IMHA) in Dogs
Harriet Woodhall (Vet News Small Animal Editor)
In a normal, healthy dog red blood cells (RBCs) live around 4 months and are then destroyed by the immune system to be replaced. In a dog with IMHA the immune system destroys RBCs prematurely as if they were a foreign virus or infection; this means they cannot be replaced at the same rate.
There are two forms of IMHA: primary (idiopathic) and secondary. In primary IMHA the body produces anti-erythrocyte (RBC) antibodies which bind to surface antigens on RBCs and lead to their destruction. Although the exact cause is unknown, there are some breeds more susceptible: Cocker Spaniels, Poodles, Old English Sheepdogs and Irish Setters. Secondary IMHA also results in antibody attachment to RBCs but occurs when the patient is exposed to a drug, toxin or has an underlying neoplastic or infectious disease.
Common symptoms include anaemia, lethargy, tachypnea (increased respiratory rate), anorexia, weakness and vomiting. Most of the symptoms arise from reduced RBCs and lack of oxygen delivery to tissues.
Diagnosis can be particularly difficult and expensive with the primary purpose to demonstrate that antibodies are attached to the surface of the RBCs. A physical exam and history need to be taken along various laboratory tests such as a Complete Blood Count and a Saline Auto-Agglutination (to evaluate the clumping of cells which arise from antibody attachment). Although the most useful starting point is Saline Auto-Agglutination it can often take a lot of laboratory tests to fully diagnose the disease.
At present there is no cure for IMHA, current treatments aim to improve RBC concentration and to stabilise the patient.
Most emergency cases need blood transfusions which try to increase haemoglobin concentrations in the blood. Transfusion products can be whole blood, red blood cells or haemoglobin concentrates with the main goal to improve oxygen delivery to the tissues. While most dogs don’t have naturally occurring alloantibodies, blood typing is still important with the universally accepted blood donor being DEA (dog erythrocyte antigen) 1.1 negative.
Another treatment method is immunosuppressive therapy using corticosteroids to slow down RBC destruction and RBC phagocytosis as well as reducing antibody production.
It is thought that T regulatory cells play a part in autoimmune diseases when there are a reduced number or they have functional defects. Therefore there is the suggestion that replacing the T-regulatory cells with those grown from stem cells would be an effective treatment for the disease. Although this seems feasible a lot more research needs to be done to ensure effective delivery of the cells and whether the treatment is practical and safe.