IMHA: When Your Pet’s Immune System Goes from Friend to Foe

When it comes to our immune system, it can either be our best friend or our worst enemy. When our pet’s immune system is healthy, it does an excellent job as the body’s defense system. When infections and diseases attempt to infect the body, the immune system’s job is to fight and prevent them from wreaking havoc.
Sometimes, however, the immune system can get out of control and begin attacking things in the body that it shouldn’t. This is the case when it comes to the immune-mediated disease known as immune-mediated hemolytic anemia, also commonly known as IMHA.

What is IMHA?

IMHA has been documented in people, dogs, cats and a wide range of other species. The disease occurs when a patient’s own immune system starts to attack the body’s red blood cells (RBCs). Once too many red blood cells have been destroyed, the patient becomes anemic. With the primary function of red blood cells being to transport oxygen to tissues, a significant decrease in their number can lead to serious complications.

What Causes IMHA?

IMHA can have no identifiable cause (idiopathic) or can be secondary to other infections occurring inside the body. Other secondary causes are drug reactions, blood parasites, cancer, and inherited red blood cell defects.
The disease is seen more commonly in dogs than cats, with female dogs being diagnosed more frequently than males. While any breed of dog can be affected with primary IMHA, certain breeds (cocker spaniels, poodles, Irish setters, and Old English sheepdogs) seem to be affected more than others. In cats, IMHA is often associated with certain underlying infections including feline leukemia virus (FeLV) and red blood cell infections (bacterial, mycoplasma, bartonella, etc.).
The age of onset for IMHA can vary but is commonly seen in young to middle-aged pets.
Signs and Symptoms of IMHA
Symptoms of IMHA can vary from mild, to severe and life-threatening. Clinical signs depend on the severity of the anemia and the underlying cause. Owners should seek veterinary care for their pets if any of these symptoms are noted:
• Pale gums
• Weakness
• Lethargy
• Jaundice (yellow gums and/or skin and eyes)
• Vomiting
• Diarrhea
• Weight loss
• Pica (eating abnormal items such as dirt)
• Dark red or brown urine
• Labored breathing

A physical exam by a veterinarian may also detect an elevated heart rate, fever, a heart murmur, or an enlarged spleen. It’s important for pet owners to seek care as soon as signs of anemia are suspected, as the symptoms can progress from mild to life-threatening quickly.

How is IMHA Diagnosed?

In addition to a complete medical history and a thorough physical exam, a veterinarian will perform a standard blood test known as a packed cell volume (PCV) if anemia is suspected. Once the diagnosis of anemia is made, additional testing that may follow is a complete blood count, chemistry profile, and infectious disease testing. These tests are useful in confirming IMHA to be the cause of the anemia and determining if the body is producing new red blood cells. Ultrasound and radiographs can assist the veterinarian in evaluating your pet’s organs and search for other underlying causes (like cancer).

How is IMHA Treated?

When beginning treatment for IMHA, there are three main goals of therapy:
1) Stabilize the patient
2) Treat any underlying cause for the IMHA, if detected
3) Suppress the immune system to stop its attack on the patient’s red blood cells

Depending on the severity of the disease process, intensive care hospitalization with red blood cell transfusions may be necessary. High doses of steroid medications are often given to suppress the immune system and control its attack on the red blood cells. Additional immunosuppressive drugs, antibiotics, and anticoagulant drugs (red blood cell destruction can result in blood clots) may also be given. Once immunosuppressive therapy is started, response to treatment is expected within one to seven days if the medications are effective. Other medications may be added as the veterinarian deems necessary.

Follow-up care generally includes repeat labwork and physical exams. It is extremely important to never stop or change your pet’s medication regiment without consulting your veterinarian first. Doing so could lead to severe crisis or relapse of the disease. Owners who have a pet that has bene diagnosed with IMHA should be prepared for the possibility of long-term medical management. Some pets will require medications for weeks to months, while others may require life-long medical management. This is decided on a case-by-case basis.

What’s the Prognosis?

IMHA is a serious disease, and mortality and humane euthanasia rates can be high. For patients that respond quickly to immunosuppressive therapy and do not require repeated transfusions, the prognosis can be good. However, if the patient requires repeated transfusions and their bodies quickly destroy transfused red blood cells, or if they have complications with blood clots, they will have a much poorer prognosis.


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