Immune-Mediated Thrombocytopenia

Causes of Immune-Mediated Thrombocytopenia in Dogs vs. Cats

IMT can be primary, meaning no underlying trigger or cause could be identified. This is the most common form of IMT in dogs. In dogs, middle-aged females develop IMT more than males. Certain breeds, such as Cocker Spaniels, Miniature Poodles, Toy Poodles, and Old English Sheepdogs are more commonly affected. There is no breed or sex predilection in cats.

IMT can also be secondary, meaning there was another event that triggered the immune system to start to overreact. In dogs, secondary causes of IMT include heartworm disease, leptospirosis, tick-borne diseases, leishmaniasis, systemic fungal infections, canine distemper virus, canine infectious hepatitis, bee envenomation, and systemic lupus erythematosus.

IMT in cats is usually secondary. Secondary causes in cats include bartonellosis (cat scratch fever), FIP, FIV, FeLV, and panleukopenia.

Secondary causes that can occur in both dogs and cats also include cystitis (inflamed bladder), pyelonephritis (infected kidney), certain cancers, IMHA, heartworms, bee envenomation, and certain drugs. There is seems to be less supportive evidence that vaccines can trigger this event.

Symptoms of Immune-Mediated Thrombocytopenia in Pets

Clinical symptoms are unlikely to be seen until the platelet level has dropped to a certain level. Your vet may find low platelets on routine blood work before your pet develops any obvious symptoms. Pets often only have one or a few symptoms.

• Bloody nose (epistaxis)
• Blood in the stool (bright red or black stools)
• Blood in vomit (bright red or coffee-ground appearing material)
• Hematoma formation
• Red dots on the gums or skin (petechia)
• Pale gums
• Blindness
• Blood in the eyes
• Seizures and other neurologic symptoms are possible, but not common
• Lethargy
• Weakness
• Enlarged lymph nodes

What tests are available to diagnose IMT?

After a complete physical exam, your vet will likely start with some routine blood work, including a CBC to look at the red and white blood cell and platelet levels. Pets with severely low platelet counts are more than likely dealing with IMT. Pets with low platelets and low red blood cells have a condition called Evan’s Syndrome.

A blood smear is often done to confirm a low platelet count. This means your vet will look at a blood sample under the microscope to count the platelets and also evaluate the size of the platelets and look for abnormal clotting/congregation of platelets.

Additional clotting function tests may be needed to see if there is a problem anywhere else in the clotting cascade. A bone marrow biopsy may be recommended if your pet has low red and white blood cells. Additional tests for infectious agents may also be recommended, along with a urine test and chemistry profile to see if a trigger for the IMT can be found.

My pet has been diagnosed with IMT. What are the potential treatment options?

Immunosuppressive medications are the main treatment course. Steroids, such as prednisone/prednisolone or dexamethasone are the most common options to start with. If the steroids are not working well enough on their own, additional immunosuppressive medications like cyclosporine and azathioprine (dogs only) are added to the treatment plan. Chlorambucil is another medication that may be used in cats.

A chemotherapeutic drug called Vincristine may be given as an intravenous injection. This often helps boost the platelet levels. This is more commonly used in dogs compared to cats.

Melatonin may also be used to help improve platelet levels.

GI protective medications may also be started. Steroids can cause GI ulceration and we don’t want to start a bleed internally! Antacids and sucralfate are common medications used to decrease this risk, especially when on high doses of steroids.

Your vet will want to monitor the platelet levels daily until your pet has at least 50,000 microliters of platelets present. Spontaneous bleeding rarely occurs at levels over 50,000. Most pets can reach this threshold within 1-2 weeks of starting steroid treatment. Once the platelets are back in the normal range (around 150,000-200,000) your vet will start slowly reducing the medications and checking the platelet level before each dose decrease. It can take 4 to 6 months to fully stop all medications.

Read more:

Immune-Mediated Hemolytic Anemia

Cancer (Neoplasia) in Cats

Vaccine Reactions in Dogs and Cats

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