Immune-Mediated Hemolytic Anemia (IMHA), also called autoimmune hemolytic anemia is a common life-threatening disease in dogs. In this disease process, dogs’ own immune system attacks its own red blood cells and destroys them.
In dogs with IMHA, Red Blood Cells (RBCs) are still being produced in the bone marrow, but once released into the circulation, they have a shorter-than-normal life span. Without adequate RBCs, the pet may be lethargic, and anorectic and blood oxygen levels may drop.
The mortality rate is high in IMHA patients without a proper treatment plan. These patients may need a long stay in the vet clinic on supportive medications, intravenous fluid therapy, blood transfusion.
All breeds can be affected but it is most common in young to middle-aged dogs.
What causes Immune-Mediated Hemolytic Anemia in dogs?
IMHA causes can be classified into two categories.
- Primary or Idiopathic IMHA
- Secondary IMHA
In primary IMHA, the dog’s own immune system destroys its own RBCs. It is done through an antibody-mediated RBC destruction mechanism without any involvement of external factors. The majority of IMHA cases are due to the primary IMHA. It is estimated that about three-quarters of cases of IMHA in dogs are primary.
In secondary IMHA, external factors play an important role in triggering a dog’s own immune system. The surface of the red blood cells becomes altered by an underlying disease process or a toxin. The dog’s immune system then recognizes the altered red blood cells as ‘foreign’ invaders that must be destroyed.
The following are few factors that may be responsible for secondary IMHA:
- Certain drugs and chemicals like penicillin, acetaminophen, sulfas, methimazole, zinc, anticonvulsants and many more
- Certain type of cancers
- Various types of vaccines
- Common allergies, insect bite, snake bite, bee stings
- Blood infections like ehrlichiosis, babesiosis etc
Once targeted, the RBCs are either destroyed within the blood vessels by a process called intravascular hemolysis or destroyed when they circulate through the liver or spleen by a process called extravascular hemolysis. In both situations, hemoglobin will be released; the liver will attempt to break down the levels of hemoglobin, increasing the workload of this organ.
What are the symptoms of IMHA in dogs?
Symptoms of IMHA are quite variable, may include some or all of the following:
- Lack of appetite
- Breathing difficulty due to anemia
- Pale mucous membrane
- Jaundice due to intravascular hemolysis
- Brown urine due to extravascular hemolysis
- Abdominal pain and fever
How is IMHA diagnosed in dogs?
The following steps and procedures may help in the diagnosis and confirmation of IMHA:
- A thorough history including vaccination, toxic exposure, travel history, ongoing medication, etc
- Physical examination
- Blood test
- Complete blood count ( CBC), may see anemia, high reticulocyte count, and neutrophilia
- Biochemical profile: may see hyperbilirubinemia, azotemia, high liver enzymes, electrolyte imbalance
- Blood film screening to see blood parasites and spherocytes. Spherocytes on blood film with other symptoms confirm your diagnosis
- Coomb’s test can be performed to detect Ig antibodies on RBCs
What is the treatment for IMHA in dogs?
The main goal is to suppress the immune response with immunosuppressive medications, treat underlying disease in secondary IMHA, and maintain hemodynamic stability. IMHA patients may need extensive care depending on the dog’s condition.
- Immunosuppression can be achieved by glucocorticoids. Initially, give Dexamethasone @ 0.25-0.5 mg/kg IV once daily. Then switch to Prednisone 2 mg/kg orally and taper it slowly over a month.
- Blood transfusion can be done if Packed Cell Volume (PCV) drops below 15 % and the pet is in respiratory distress.
- In some cases, with a minimum response to immunosuppressive therapy, corticosteroids. Azathioprine @ 2 mg/kg or Cyclosporine @ 4 mg/kg can be tried.
- Intravenous fluid therapy is given to maintain sufficient tissue perfusion.
- If relapse occurs, then splenectomy may be considered.
- Other supportive medications like antacid, antibiotic, and antiemetic should be given with the main treatment protocol.
Your veterinarian will outline a treatment plan specific for your dog’s needs, based on diagnostice test results. With complex cases, your veterinarian may recommend a referral to an internal medicine specialist.
What is the prognosis for IMHA?
The prognosis for dogs with IMHA is based on the specific diagnosis, as well as the dog’s general condition at the time of diagnosis. In many cases, the patient’s condition can be managed with appropriate drug treatments. Once the patient’s condition improves and the anemia resolves or stabilizes, your veterinarian will recommend tapering off the immunosuppresive medications over a period of several months to lessen any side effects associated with therapy. Since relapses are common with this disease, you will need to monitor your dog closely as medications are decreased or discontinued.