Immune-Mediated Thrombocytopenia (ITP) in Dogs

What Is Immune-Mediated Thrombocytopenia in Dogs?

Immune-mediated thrombocytopenia (ITP) in dogs is a blood disease in which the dog’s immune system attacks and destroys the body’s platelets. ITP is a serious disease and is common in middle-aged dogs.

ITP can be classified as either a primary or secondary disease. In primary, or idiopathic, ITP, there’s no known reason why the immune system is destroying the body’s platelets. In secondary ITP, the immune system destroys platelets in response to an underlying condition, such as cancer, infection, or toxin or drug exposure.

Due to the severity of ITP’s effects, the disease is a medical emergency and should be treated by your dog’s veterinarian or the nearest veterinary emergency hospital as soon as possible.

What Are Platelets?

Platelets are a type of blood cell that play an important role in blood clotting. Platelets are produced in the bone marrow and released into the bloodstream.

Dogs normally have between 200,000 and 500,000 platelets per microliter of blood, but only 20,000 to 50,000 per microliter are needed to prevent spontaneous bleeding and bruising. 

Platelets are stored in the spleen and travel through the bloodstream to areas of blood vessel damage. There, they bind together and form a plug to seal the hole in the leaking vessel. If damaged blood vessels are not repaired quickly by the platelets, bleeding—ranging from a small bruise to serious internal hemorrhaging—can occur.

Platelets are normally removed from the body by the liver if they are not used within eight to 12 days. This, in turn, signals the bone marrow to make new platelets.

Although dogs with ITP produce platelets normally, the platelets are destroyed by the immune system after approximately one day. They aren’t regenerated quickly enough to resolve the symptoms before a dog could succumb to this condition.

Symptoms of Immune-Mediated Thrombocytopenia in Dogs

Since platelets form blood clots to stop and prevent bleeding, a platelet deficiency caused by ITP typically causes internal bleeding and bruising. Signs you may observe in your dog include:

• Abnormal bruising

  • Petechiae: Small pinpoint bruises found on skin and mucosal surfaces (e.g., gums, vulva, or penis)

  • Ecchymoses: Large bruises

• Abnormal bleeding

  • Melena: Black, tarry stool from bleeding in the stomach or upper small intestines

  • Bloody diarrhea or blood in the stool

  • Bleeding from the gums

  • Epistaxis (nosebleed)

  • Blood spots in the eyes

  • Hematemesis (bloody vomit)

  • Bloody vaginal discharge

  • Blood in the urine

• Lethargy

• Reluctance to exercise

• Decreased appetite

• Pale mucus membranes

• Fever

• Enlarged lymph nodes

• Rapid or difficulty breathing

• Anemia, which may develop from blood loss

Causes of Immune-Mediated Thrombocytopenia in Dogs

ITP is a relatively common disease that occurs most often in middle-aged, female dogs.

While any dog breed can be affected by ITP, including mixed-breed dogs, Cocker Spaniels, Standard and Toy Poodles, and Old English Sheepdogs are thought to have a genetic predisposition. A familial predisposition has been seen in families of Cocker Spaniels and Scottish Terriers.

Primary ITP is more common than secondary ITP in dogs. Triggers for secondary ITP include:

• Medications

  • Sulfa, cephalosporin, and penicillin antibiotics

  • Phenobarbital

  • Fenbendazole

• Infectious diseases

  • Tick-borne diseases (e.g., Lyme disease, babesiosis, ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever)

  • Leishmaniasis

  • Leptospirosis

  • Heartworm disease

  • Parvo

  • Canine distemper

  • Salmonellosis

• Cancer, most commonly lymphoma and hemangiosarcoma

• Disseminated intravascular coagulation (DIC)

• Toxins (e.g., zinc and xylitol)

• Venomous snake bites

While it has been suspected that ITP may also be a rare side effect of vaccine administration, studies have not proven an association.

How Veterinarians Diagnose Immune-Mediated Thrombocytopenia in Dogs

If your dog is showing signs of ITP, particularly abnormal bruising or bleeding, your veterinarian will take a complete medical history, including any medications your dog is taking and recent tick exposure. If your dog has a familial connection that predisposes them to ITP, it is important to inform the veterinary team.

Your vet will then perform a physical examination and likely recommend diagnostic testing. Blood work may include:

• A complete blood count (CBC), which includes a total platelet count

• A biochemistry profile, which is the checking of organ function and electrolytes

• Coagulation times, to make sure a dog’s body can perform a blood clot properly

• Tick disease panel, to check for tick-borne diseases such as Lyme

Additionally, a urinalysis and fecal evaluation are typically performed.

Your dog’s blood can also be evaluated under a microscope to confirm low platelet numbers. Additional testing, such as a bone marrow biopsy and imaging techniques, including X-rays and ultrasound, can assess for other underlying causes of ITP.

Primary ITP is a diagnosis of exclusion, meaning that all causes of secondary ITP must first be ruled out.

Treatment of Immune-Mediated Thrombocytopenia in Dogs

Dogs with ITP are usually hospitalized for stabilization and treatment. Treatment may include a blood transfusion, especially if a sudden and excessive blood loss occurred, or a plasma transfusion to help increase platelet numbers quickly.

The mainstay of ITP therapy is medication to suppress the immune system, to stop your dog’s body from destroying its platelets. Steroids such as prednisone are often used, and although they can cause undesirable side effects, including increased thirst, urination, and hunger, the benefits outweigh these short-lived effects.

Supportive care measures, such as supplemental oxygen, IV fluids, antibiotics, and anti-nausea medications, may be used depending on your dog’s symptoms. Rarely, if medications do not control a dog’s ITP or the condition recurs repeatedly, a splenectomy—a surgical procedure to remove the spleen—may be performed.

In ITP, a dog’s immune system attacks platelets. The spleen then removes those platelets from the body. If the spleen is removed, then a dog will have more platelets because the organ won't be removing them.

Recovery and Management of Immune-Mediated Thrombocytopenia in Dogs

Once your dog is feeling better and returns home, they will need frequent veterinary rechecks to monitor their progress and therapy.

Immunosuppressive medications are often continued for several months and sometimes for the rest of the dog’s life, depending on the underlying cause of the ITP. With this treatment, the goal is to find the lowest possible dose of medication to keep the immune system at bay.

Most dogs can live a long, happy life after an ITP diagnosis, especially if the underlying cause is treated promptly and aggressively. Full recovery occurs in 70% to 90% of dogs with ITP.

Indications that a dog might not recover completely include:

• Black, tarry stool

• Increased blood urea nitrogen test (BUN)

• Underlying illness severe enough to warrant a blood transfusion

ITP recurrence can be as high as 30% and often occurs two to three months after the initial diagnosis. Removal of the spleen results in remission in 60% of dogs affected with recurrent ITP. 

Unfortunately, for dogs who can’t tolerate immunosuppressive medications, blood transfusions, or splenectomy surgery, ITP can be fatal or may warrant humane euthanasia.

Prevention of Immune-Mediated Thrombocytopenia in Dogs

Some causes of secondary ITP can be prevented. Year-round tick prevention is important for all dogs, and especially for dogs who spend a lot of time outside, particularly in the woods or hiking.

Preventing exposure to infectious diseases and venomous snakes can also help decrease your dog’s risk.