Immune-Mediated Hemolytic Anemia (IMHA)

 

Overview

• Immune-Mediated Hemolytic Anemia (IMHA) is a disorder in which the immune system mistakenly attacks and destroys red blood cells (RBCs), leading to anemia.

• This condition can be primary (idiopathic) or secondary, meaning it may arise as a result of another underlying condition, such as an infection, cancer, or drug reaction.

• Dogs with IMHA can experience a rapid onset of symptoms due to the loss of red blood cells and decreased oxygen-carrying capacity.

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Etiology

• Primary IMHA (idiopathic): No known underlying cause, but it is thought to be an immune dysregulation that leads to the destruction of RBCs.

• Secondary IMHA: Triggered by external factors like:

  • Infections (e.g., ehrlichiosis, babesiosis),

  • Medications (e.g., sulfonamides, penicillins),

  • Cancer (e.g., lymphoma, hemangiosarcoma),

  • Vaccinations or other immune triggers.

• Certain breeds (like Cocker Spaniels, Schnauzers, Irish Setters) have a predisposition to developing IMHA.

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Clinical Signs

• Pale or jaundiced mucous membranes (due to hemolysis and bilirubin release).

• Tachycardia (rapid heart rate) and tachypnea (rapid breathing) due to anemia.

• Lethargy, weakness, and exercise intolerance.

• Anorexia (loss of appetite) and vomiting in severe cases.

• Splenomegaly and hepatomegaly in some cases due to organ involvement in clearing damaged RBCs.

• Dark, red or orange-colored urine (due to the presence of hemoglobin from lysed RBCs).

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Diagnosis

• Complete Blood Count (CBC):

  • Regenerative anemia with spherocytes (small, round RBCs) present.

  • Reticulocytosis (increased immature RBCs) suggests regenerative anemia.

• Direct Coombs' Test: This test detects the presence of autoantibodies against RBCs, confirming the diagnosis of IMHA.

• Blood Smear: Examination of RBC morphology to identify spherocytes and agglutination (clumping of RBCs).

• Biochemistry: May reveal elevated bilirubin due to hemolysis.

• Ultrasonography/Imaging: To check for underlying causes like splenomegaly or hemangiosarcoma.

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Treatment

• Immunosuppressive therapy:

  • Corticosteroids (e.g., prednisone) are the first-line treatment to suppress the immune system and reduce RBC destruction.

  • Other immunosuppressive agents: Azathioprine, mycophenolate mofetil, or cyclophosphamide may be added if steroids are insufficient.

• Blood transfusions: To address severe anemia or when the dog is in hypovolemic shock.

• Supportive care: IV fluids, nutritional support, and anti-ulcer medications (as steroids can cause GI ulcers).

• Treating underlying causes: If IMHA is secondary to an infection or cancer, treating the primary disease is crucial.

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Immune-Mediated Thrombocytopenia (IMTP)

 

Overview

Immune-Mediated Thrombocytopenia (IMTP) is a disorder in which the immune system targets and destroys platelets, the blood cells responsible for clotting. This leads to thrombocytopenia (low platelet count), which increases the risk of bleeding, petechiae, and hemorrhaging. IMTP can be primary (idiopathic) or secondary to other conditions such as infections, medications, or cancer.

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Etiology

• Primary IMTP (idiopathic): The exact cause is unknown, but it is believed that a dysregulated immune response leads to the destruction of platelets.

• Secondary IMTP: Triggered by:

  • Infections (e.g., ehrlichiosis, leptospirosis),

  • Medications (e.g., sulfonamides, vaccinations),

  • Neoplasia (e.g., lymphoma or hemangiosarcoma),

  • Other immune-mediated diseases like IMHA.

Certain breeds such as Cocker Spaniels, Schnauzers, and Doberman Pinschers are predisposed to developing IMTP.

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Clinical Signs

• Petechiae and ecchymosis (bruising) on the skin, mucous membranes, or conjunctiva.

• Epistaxis (nosebleeds), hematemesis (vomiting blood), or melena (black, tarry stools due to gastrointestinal bleeding).

• Lethargy, weakness, and pale mucous membranes due to internal bleeding.

• Prolonged bleeding from small cuts or surgical incisions.

• In severe cases, spontaneous internal bleeding can occur, leading to shock and collapse.

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Diagnosis

• Complete Blood Count (CBC):

  • Thrombocytopenia (low platelet count) is the hallmark.

  • Platelet morphology may show platelet clumping, but this is not specific.

• Bone Marrow Aspiration: To rule out other causes of thrombocytopenia such as bone marrow disorders or neoplasia.

• Coagulation panel: To rule out other clotting disorders and to assess for coagulopathy.

• Direct Coombs' Test: To detect autoantibodies against platelets, confirming the immune-mediated cause.

• Serologic testing: For infectious diseases like Ehrlichia or Leptospirosis if secondary IMTP is suspected.

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Treatment

• Immunosuppressive therapy:

  • Corticosteroids (e.g., prednisone) are the first-line treatment for suppressing immune-mediated platelet destruction.

  • Other immunosuppressive drugs: If steroids are insufficient, azathioprine, cyclophosphamide, or mycophenolate mofetil may be used.

• Platelet transfusions: In severe cases of thrombocytopenia with active bleeding, a platelet transfusion may be required.

• Supportive care: IV fluids, GI protectants (e.g., sucralfate) to prevent GI ulceration from steroids, and antibiotics if there is a risk of secondary infection.

• Treat underlying causes: If IMTP is secondary to an infection, neoplasia, or another disease, the underlying condition must also be treated.