Hey there, pet parents. Today we're going to delve into the complex and serious world of Immune-Mediated Diseases. These are conditions where the dog's immune system, which is supposed to protect the body from foreign invaders, gets confused and starts to attack the body's own cells. We're going to focus on two of the most common and life-threatening examples: IMHA and ITP.
What is Immune-Mediated Disease?
The immune system has a remarkable ability to recognize "self" from "non-self." In an immune-mediated disease, this recognition system breaks down. The immune system mistakenly flags a certain type of the body's own cells as being foreign and launches a full-scale attack to destroy them.
We don't always know what triggers this, but it can be a primary, idiopathic problem, or it can be secondary to something else that has revved up the immune system, like a recent infection, a vaccine, or even cancer.
Immune-Mediated Hemolytic Anemia (IMHA)
What is it?
In IMHA, the immune system attacks and destroys the body's own red blood cells. "Hemolytic" means the destruction of red blood cells, and "anemia" means a low red blood cell count.
Red blood cells are responsible for carrying oxygen from the lungs to the rest of the body. Without enough of them, the body becomes starved of oxygen. IMHA is a very serious and life-threatening disease with a mortality rate as high as 50%.
Signs of IMHA:
The signs are those of severe anemia:
- •Extreme Lethargy and Weakness: The dog may be unable to even stand or lift its head.
- •Pale Gums: The gums will be white or very pale pink instead of a healthy pink.
- •Jaundice or Icterus: The skin, gums, and whites of the eyes may have a yellow tinge. This is because the massive destruction of red blood cells releases a large amount of bilirubin (a yellow pigment).
- •Rapid, Weak Pulse.
- •Rapid Breathing.
- •Dark, Orange-Colored Urine.
Diagnosis and Treatment:
- •Diagnosis: Bloodwork will show a severe anemia. A "slide agglutination" test can be done, where a drop of blood is mixed with saline. In a dog with IMHA, the antibody-coated red blood cells will clump together.
- •Treatment: This is a true medical emergency that requires intensive hospitalization. The treatment has two goals:
- •Stop the Destruction: High doses of immunosuppressive drugs, mainly steroids like prednisone, are used to shut down the immune system's attack. Other immunosuppressants like cyclosporine or mycophenolate may also be used.
- •Support the Patient: The dog will need one or more blood transfusions to provide them with enough red blood cells to carry oxygen while they are waiting for the immunosuppressive drugs to work. They will also need IV fluids and other supportive care.
Immune-Mediated Thrombocytopenia (ITP)
What is it?
In ITP, the immune system attacks and destroys the body's own platelets. "Thrombo" means platelet, and "penia" means a low count.
Platelets are the tiny cells in the blood that are responsible for forming a blood clot. Without enough platelets, the dog cannot clot its blood properly, which can lead to spontaneous and uncontrolled bleeding.
Signs of ITP:
- •Petechiae: This is the hallmark sign. These are tiny, pinpoint bruises that are most often seen on the gums or the belly.
- •Ecchymoses: Larger, blotchy bruises.
- •Nosebleeds (Epistaxis).
- •Blood in the Urine or Stool.
- •Prolonged Bleeding from a minor cut.
- •Lethargy.
Diagnosis and Treatment:
- •Diagnosis: Bloodwork will show a severely low platelet count. A normal platelet count is over 200,000. In a dog with ITP, it can be less than 10,000. Your vet will also need to rule out other causes of a low platelet count, like certain tick-borne diseases.
- •Treatment: Just like IMHA, ITP is an emergency that requires hospitalization.
- •Immunosuppression: High doses of steroids are the cornerstone of treatment. A drug called vincristine is also sometimes given, as it can stimulate the bone marrow to release more platelets.
- •Transfusions: If the dog is actively bleeding, they may need a platelet transfusion or a whole blood transfusion.
- •Strict Rest: The dog must be kept very quiet and confined (cage rest) to prevent any bumps or bruises that could lead to bleeding.
Prognosis
Both IMHA and ITP are very serious diseases. Even with aggressive treatment, they can be fatal. The first few days are the most critical. If a dog can survive the initial crisis, they will need to be on immunosuppressive medications for several months, and the dose will be slowly tapered down. Relapses are possible.
These are scary diseases, but a rapid diagnosis and aggressive treatment can give your dog the best possible chance of survival.
Sources & Further Reading:
- •VCA Animal Hospitals - Immune-Mediated Hemolytic Anemia (IMHA) in Dogs and Immune-Mediated Thrombocytopenia (ITP) in Dogs
- 1Merck Veterinary Manual - Immune-Mediated Disease in Small Animals