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Understanding Immune-Mediated Hemolytic Anemia (IMHA)

By Dr. Ryan Chuang


What is IMHA?

IMHA in dogs and cats

The immune system is designed to clear pathogens and abnormal cells. However, in cases of IMHA, the immune system mistakenly identifies its own red blood cells as "foreign" and begins to destroy them.

  • IMT/IMTP: Sometimes the immune system attacks platelets instead, leading to low platelet counts (Immune-Mediated Thrombocytopenia).

  • Evans Syndrome: When the body attacks both red blood cells and platelets simultaneously.


Common Symptoms

  • Severe weakness, lethargy, or fainting.

  • Poor appetite, vomiting, or diarrhea.

  • Jaundice: Yellowing of the skin, gums, or the whites of the eyes.

  • Dark brown or tea-colored urine.

  • Pale gums (mucous membranes).

  • Rapid breathing or panting due to oxygen deficiency.

  • If platelets are low: Bruising (petechiae), bloody stools, or black, tarry stools, urine with blood


Causes of IMHA

  1. Primary (Idiopathic): An underlying immune system malfunction. This is the most common cause in dogs.

  2. Secondary: Triggered by an external factor. This is more common in cats. Triggers include:

    • Infections

    • Tumors/Cancer

    • Certain medications

    • Inflammatory diseases (Pancreatitis, Cholecystitis, Cystitis, etc.)


Treatment Protocols

  • Corticosteroids: High doses are essential to suppress the overactive immune system.

  • Immunosuppressants: Additional drugs (e.g., Cyclosporine or Azathioprine(Dog only) or mycophenolate, etc) are often used for better control.

  • Antithrombotic Drugs: IMHA often causes abnormal blood clotting (thrombosis), which is a leading cause of death. Preventive medication is crucial.

  • Human Intravenous Immunoglobulin (IVIG): Used in severe cases to neutralize the abnormal immune response.

  • Blood Transfusion: Necessary in emergency situations to stabilize the patient, though it does not cure the underlying disease.

  • Splenectomy: Surgical removal of the spleen may be considered for refractory cases, as the spleen is a primary site for red blood cell destruction.


Prognosis and Long-term Care

IMHA is a life-threatening condition with a high mortality rate if not managed properly.

  • Duration: Treatment usually lasts at least 3 to 6 months.

  • Strict Compliance: Never stop or reduce medication without veterinary guidance.

  • Vaccination Note: Since vaccines stimulate the immune system, pets that have recovered from IMHA/IMT are generally advised against future vaccinations to prevent relapse.


(Article by Dr. Ryan Chuang. Reproduction without permission is prohibited; sharing with original attribution is welcomed.)


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