Evans syndrome in dogs is a condition that occurs when the dog’s immune system attacks the red blood cells and platelets. The end result is anemia (low red blood cell counts) and poor clotting ability due to low platelets. To help dog parents navigate this scary diagnosis, integrative veterinarian Dr. Julie Buzby explains the causes, symptoms, diagnosis, treatment, and prognosis for Evans syndrome in dogs.
One of the first things veterinarians check in dogs and cats who aren’t feeling well is their gum color. In a healthy animal, the gums should generally be a nice, bubblegum pink color. Or in a dog with pigmented gums, a mottled pinkish-brown appearance can be normal, too.
What vets hope never to find are pale, grey, or yellowish gums, as this can be a red flag for a number of diseases. One is a severe immune-mediated condition known as Evans syndrome.
What is Evans syndrome in dogs?
Evans syndrome is a life-threatening condition that causes anemia and reduced clotting ability due to the destruction of both red blood cells and platelets. More specifically, the dog has a combination of immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP).
A dog develops Evans syndrome when the immune system mistakenly attacks the body’s own red blood cells (causing anemia) and platelets (causing thrombocytopenia—low platelets). This occurs because the immune system starts seeing the red blood cells and platelets as foreign. Since more than one cell line is targeted, Evans syndrome could be considered a “double whammy” of immune-mediated diseases.
How do dogs get Evans syndrome?
Evans syndrome can be a primary (“stand-alone”) disease, or it can develop secondary to another problem. Primary Evans syndrome is an idiopathic disorder. This means there’s no known underlying cause for the targeted destruction of the red blood cells and platelets.
Less commonly, dogs may develop secondary Evans syndrome as a result of:
- Underlying infections: Leptospirosis, distemper, tick-borne diseases in dogs, intestinal parasites, heartworms, etc., can trigger Evans syndrome.
- Recent vaccinations: The link between vaccinations and Evans syndrome is tentative. Please consult with your vet to determine which vaccines are right for your dog.
- Drug reactions: Certain antibiotics or other medications may trigger Evans syndrome.
- Certain types of cancer, like leukemia or lymphoma.
- Inflammatory diseases or other autoimmune conditions: Pancreatitis in dogs, UTI in dogs, SLE in dogs, etc., may be linked to Evans syndrome.
- Snake bite on a dog or bee stings.
Evans syndrome itself isn’t contagious since it is caused by an abnormal immune reaction. However, some of the triggers of Evans syndrome, such as infectious diseases, are contagious.
Which dogs are prone to Evans syndrome?
A breed predilection to Evans syndrome exists in Cocker Spaniels, Old English Sheepdogs, and Poodles. It also seems to occur more commonly in middle-aged dogs.
What are the symptoms of Evans syndrome in dogs?
Symptoms of Evans syndrome often develop quickly and stem from the effects of having low platelets and low red blood cells. Dogs can often become acutely ill. Common clinical signs include:
Sudden weakness or collapse
Evans syndrome involves the destruction of red blood cells (hemolysis), which carry oxygen to all of the body’s vital tissues and organs. The reduced oxygen delivery to the tissues can make the dog weak and low on energy.
In severe cases, the dog may collapse and be unable to get up again. This is an emergency.
Pale gums
Red blood cells help give the gums their bubblegum pink color. Thus, anemia in dogs can cause pale pink or white gums.
Yellow discoloration to gums, skin, and eyes
When red blood cells break apart, they release hemoglobin (Hb). The liver converts hemoglobin into bilirubin, a yellow pigment that the body normally excretes in the bile. With rapid red blood cell destruction, excess bilirubin accumulates in the tissues more quickly than the liver can excrete it. This causes a yellowish discoloration of the gums, whites of the eyes, and skin.
Due to the presence of bilirubin, the urine may be a dark yellow or orange color.
Bruising
Bruising can occur when platelet destruction interferes with the body’s normal ability to clot blood. These bruises may show up as large, singular areas of discoloration (hematomas). Or they may be clusters of tiny spots or patches (petechiae or ecchymoses) on your dog’s skin or gums.
Spontaneous bleeding
The dog may experience bleeding gums, dog nose bleeds (epistaxis), blood in the urine (hematuria), or blood in the feces (hematochezia).
Blindness
Bleeding within the eye can lead to increased intraocular pressure and damage to the retina. The end result may be vision loss.
Seizures
Neurologic signs, such as seizures in dogs, may develop if bleeding occurs in or around the brain.
Increased heart rate and respiratory rate
You might notice your dog breathing fast or his or her heart beating faster. These are signs the body is trying to compensate for the decreased blood volume and a lack of oxygen-carrying red blood cells in circulation.
Heart murmur
When a dog is anemic, the blood becomes thinner than usual. Instead of the vet hearing the normal steady “lub-dub” of the heartbeat, the thinner blood causes a soft “whooshing” sound superimposed over the heartbeat as it flows through the heart. This is a heart murmur in dogs.
Blood clots
Dogs with IMHA may be prone to forming blood clots (thromboembolisms). These clots can obstruct normal blood flow to vital organs like the liver, kidneys, and lungs.
Additionally, dogs can develop a life-threatening condition called disseminated intravascular coagulation (DIC). In DIC, the body first forms many clots, then loses the ability to continue clotting. Sadly, DIC has the potential to cause organ failure and death in some cases.
Organ failure
Organ failure may develop if vital organs like the lungs, liver, and kidneys go without oxygen for too long. Oxygen deprivation results from blood clots and/or insufficient oxygen-carrying red blood cells in circulation.
If you see these signs, head to the vet
If your dog starts showing some of these symptoms at home, bring him or her to your regular veterinarian or emergency vet immediately. Evans syndrome can be life-threatening. The sooner your dog receives a diagnosis and starts treatment, the better.
How will the vet diagnose a dog with Evans syndrome?
At the visit, the veterinary team will go over your dog’s medical history, including any recent vaccinations and current medications. The vet will also perform a complete physical exam. This allows him or her to evaluate your dog’s gum color, check the heart and respiratory rate, listen for a heart murmur, look for bruising or bleeding, and detect other abnormalities.
Diagnostic tests
Then the vet will discuss the recommended diagnostic tests. Evans syndrome often requires several tests to make an accurate diagnosis.
- Baseline lab work: Often, the vet will want to run blood tests for dogs, including:
- Complete blood count: This test measures your dog’s red blood cell (RBC), white blood cell (WBC), and platelet counts. It is not uncommon for Evans syndrome to cause decreased RBC and platelet levels, but a significant increase in WBC levels. The CBC also helps rule out infections or certain types of cancer, like leukemia or multiple myeloma.
- Chemistry panel: The chemistry panel helps screen for damage to the kidneys, liver, or other organs and gives the vet an overall snapshot of the dog’s health status.
- Clotting tests: In dogs with bleeding issues, clotting tests help give a better overall picture of what is going on with the various components that play a role in blood clotting.
- Coombs test: This is a specialized test that identifies the presence of red blood cell antibodies in cases of immune-mediated RBC destruction. A positive Coombs test points to IMHA.
- Tick titers: If you live in an area where ticks are common, your vet may recommend testing for tick-borne diseases like Ehrlichiosis, Lyme disease, or Rocky Mountain Spotted Fever (RMSF). Those diseases can trigger Evans syndrome or have similar symptoms.
- Bone marrow aspirate: The bone marrow is responsible for producing stem cells, which mature into the RBCs, WBCs, and platelets that circulate in the bloodstream. Evaluating a bone marrow sample helps identify abnormal cell development and screens for cancer cells. This procedure requires sedation and a local block for additional pain relief since sample collection can be very uncomfortable.
- Imaging: X-rays, CT scans, or abdominal ultrasound are valuable diagnostic tools if the vet suspects cancer is the underlying trigger.
What is the treatment for Evans syndrome in dogs?
Treatment for Evans syndrome focuses on suppressing the body’s abnormal immune response to slow (or ideally stop) the destruction of red blood cells and platelets. Plus, it will be important to address the underlying cause (if present) and support the dog while the medications take effect.
Severely affected dogs may need to be hospitalized for intensive monitoring and treatment. This might occur at your family veterinarian’s office or a 24-hour specialty hospital. Then once the dog is stable, he or she can go home for continued treatment.
Immunosuppressive medications
Steroids such as dexamethasone or prednisone for dogs are typically the first line of defense in treating Evans syndrome. However, your vet may prescribe other immunosuppressive medications (cyclosporine, azathioprine, mycophenolate, leflunomide) if your dog experiences adverse side effects from the steroids or does not respond sufficiently.
Once the dog’s platelet and RBC numbers have normalized and stayed steady, the vet will attempt to wean your dog off the immunosuppressants or get to the lowest dose that keeps the Evans syndrome under control. This process often takes about 4-6 months.
Note: If your dog is on immunosuppressants, do not stop the medication or alter the dose without speaking with your veterinarian. Withdrawing these medications too quickly may lead to a relapse, which is sometimes more severe than the initial episode.
Whole blood transfusion
Depending on the severity of your dog’s anemia, a whole blood transfusion may be necessary. Whole blood supplies red blood cells, white blood cells, and platelets to the body.
Your dog’s immune system may inadvertently destroy some of the newly transfused cells during the initial stages of treatment. However, a transfusion is still beneficial and potentially lifesaving. It buys time for the immunosuppressive medications to start working, allowing the bone marrow to catch up with the demand for new red blood cells and platelets.
Antibiotics or other treatments for the underlying disease
Your veterinarian may prescribe antibiotics like doxycycline if he or she suspects your dog has a tick-borne disease. Or he or she may start other treatments specific to any concurrent diseases your dog has that might have triggered the Evans syndrome.
Anticoagulants
Some vets will put dogs with Evans syndrome on medications like Plavix or aspirin to help prevent the formation of blood clots, which can obstruct the blood vessels. However, in a dog with extremely low platelet numbers, vets may avoid using anticoagulants until the platelet count improves.
Additional therapies for IMHA or ITP
In addition to immunosuppressants, sometimes the vet may suggest treatment options such as:
- Melatonin for dogs: Studies indicate that melatonin may encourage the platelet precursors in the bone marrow to make more platelets.
- Human intravenous immunoglobulin (IVIG): A dose of human IVIG may temporarily decrease the immune system’s destruction of platelets and RBCs.
- Plasmapheresis (therapeutic plasma exchange): Exchanging the fluid portion of a dog’s blood (plasma) that contains the immune system molecules targeting red blood cells and platelets with the plasma of a healthy dog may sometimes be helpful.
- Vincristine: A dose of this chemotherapeutic drug may help boost platelet numbers.
- Romiplostim: One of the medications used for ITP in humans, Romiplostim, may be useful for dogs with ITP, too. In a 2024 Journal of Veterinary Internal Medicine study on Romiplostim for treatment of low platelets in dogs, 18 of 20 dogs with primary ITP who received Romiplostim experienced an increase in platelet count. More research is needed on this treatment, but it is exciting to see what the future may hold.
What kind of monitoring will dogs with Evans syndrome need?
If your dog was diagnosed with Evans syndrome, you can expect to be making frequent vet visits for monitoring, especially at the start of treatment. The vet may want to assess your dog’s red blood cell numbers and platelet numbers every few days once your dog is discharged from the hospital.
As the numbers hopefully normalize, the rechecks can become less frequent. However, you will still need to bring your dog in regularly for monitoring, especially when attempting to wean off the immunosuppressants.
What is the prognosis for dogs with Evans syndrome?
Evans syndrome in dogs can, unfortunately, be life-threatening in some cases. However, there are also dogs who recover well.
In general, more mildly affected dogs with primary Evans syndrome can have a good prognosis with prompt diagnosis and treatment. However, dogs with extremely low cell counts or severe clinical signs and those who don’t respond well to treatment have a poorer prognosis.
In dogs with secondary Evans syndrome, the prognosis varies depending on how well the underlying cause can be treated or managed.
Relapses may develop in as many as 40% of dogs with Evans syndrome after discontinuation of their treatment regimen. Thus, diligent at-home monitoring and regular recheck visits with your dog’s veterinary team are essential. Plus, it is important to keep in mind that some dogs may end up needing to be on immunosuppressants long-term.
Work with your vet
It can be scary to find out your dog has a condition like Evans syndrome and to be facing a lot of uncertainty, medications, and rechecks in the future. However, you don’t have to do it alone. Your dog’s veterinary team (your family vet and the ER or internal medicine vets if you end up at a specialty hospital) will be with you every step of the way.
Catching the signs of Evans syndrome quickly and relying on your veterinary team gives your beloved dog the best chance for recovery and a good quality of life at home. And of course, all the TLC and careful monitoring you provide will help, too!
If you’d like to learn more about the two components of Evans syndrome—IMHA and ITP—check out these two articles:
Has your dog been diagnosed with Evans syndrome?
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