Evans Syndrome in Dogs
In 1951, Dr. Robert Evans and associates studied the relationship between autoimmune conditions affecting red blood cells and autoimmune conditions affecting platelets in people, developing the first list of diagnostic criteria for Evans syndrome, a dangerous condition that can affect both humans and our pets.
While not super common in canines, Evans syndrome in dogs is a serious and life-threatening medical condition, and we want you to be prepared to help your dog should the symptoms arise. Here, we’ll explain what Evans syndrome is, symptoms to watch for, and treatment options.
What Is Evans Syndrome?
Evans syndrome is the name given to the condition that arises when the immune system is attacking and destroying both the dog’s red blood cells and platelets.
When the body attacks only the red blood cells, which are important for carrying oxygen throughout the body, this is called immune-mediated hemolytic anemia (IMHA). When the body attacks only the platelets, which are essential for clotting, this is called immune-mediated thrombocytopenia (IMTP). With Evans syndrome, you have both IMHA and IMTP concurrently.
When Evans syndrome occurs, damaged cells are removed from the bloodstream by the liver and spleen. The destruction and removal of these cells leaves the dog at severe risk for significant anemia and spontaneous bleeding.
This is absolutely a medical emergency! Your pet will need emergency care at a veterinary clinic, so don’t watch and wait if you’re concerned about Evans syndrome.
Causes of Evans Syndrome in Dogs
Your dog may have no known underlying cause of Evans syndrome, which is called primary or idiopathic Evans syndrome. When the syndrome has a known trigger, it’s considered secondary.
Potential causes of secondary Evans syndrome include:
- Infection, often diseases transmitted by ticks
- Recent vaccination
- Starting a new medication
In these situations, the immune system has been stimulated and over-reacts, targeting the pet’s own red blood cells and platelets.
In some cases, genetics may play a role. Dog breeds more likely to develop Evans syndrome include Cocker Spaniels and Old English Sheepdogs. Dogs whose relatives have had Evans syndrome may be at an increased risk. However, any breed of dog can develop Evans syndrome, including mixed breed pups and those with no family history of Evans syndrome.
Symptoms of Evans Syndrome
Dogs with Evans syndrome are usually critically ill. If you’re noticing symptoms of Evans syndrome, you need to get your pet to an emergency veterinarian as soon as possible.
- Pale mucous membranes (pale gums, conjunctiva around eyes, genitals)
- Lethargy and weakness
- Rapid breathing
- Bruises in the skin or mouth (can be pinpoint or larger)
- Bleeding from the nose or mouth
- Blood in the urine or feces
With Evans syndrome, we are seeing symptoms of both anemia (typical of IMHA) and bleeding or bruising (typical of IMTP).
Diagnosing Evans Syndrome in Dogs
The emergency veterinarian will perform a quick but thorough physical exam of your pet. Signs they may notice that suggest Evans syndrome include bruising, lethargy, pale mucous membranes, a high heart rate, a heart murmur, high respiratory rate, fever, and blood on rectal palpation. Your veterinarian will want to rule out exposure to anticoagulants (rat bait, human medications) and trauma (hit by a car).
Testing for Evans syndrome can include:
- Complete blood count (CBC) and blood chemistry
- Looking at blood under a microscope
- Coagulation testing
- Slide agglutination test
- Direct Coombs test
- Screening for tick-borne disease
- X-rays of the chest and abdomen
- Ultrasonographic exam of the abdomen
Your dog’s CBC would show low red blood cell numbers, low platelet numbers, and potentially high white blood cell numbers (as the immune system is overreacting). On review of a microscopic slide, your veterinarian may notice that there are very few platelets, that some red blood cells appear abnormally small (spherocytosis), and that young red blood cells are being released into circulation to replace dying red blood cells (reticulocytosis).
Your pet’s lab work may also provide evidence of abnormal organ function, such as elevated liver enzymes. This is often due to the stress of anemia on the organs, which require oxygen and good blood flow to function appropriately.
A slide agglutination test can indicate whether your dog has IMHA but does not definitively diagnose Evans syndrome (both IMHA and IMTP). A drop of blood from an EDTA anticoagulant tube is placed on a slide with 1-2 drops of saline and gently rocked back and forth. With IMHA, the blood cells will clump together (agglutinate), forming a speckled appearance on the slide. The veterinarian will examine the slide under a microscope to confirm. While a positive slide agglutination test can be indicative of IMHA, a negative slide agglutination test does not rule out IMHA.
A direct Coombs test (also called a direct antiglobulin or DAT) identifies antibodies on the surface of red blood cells. If the CBC and chemistry results are suggestive of IMHA and your dog has a positive Coombs test, they will be diagnosed with IMHA. False negative tests do occur. Like the slide agglutination test, the direct Coombs test can’t tell you if the pet has concurrent IMTP, which is a component of Evans syndrome.
Ticks carry diseases that can cause Evans syndrome in dogs. Ruling out these diseases involves laboratory testing of blood and examining the blood cells under a microscope. You may have also heard of a 4Dx SNAP test. This test screens not just for heartworms but also for Lyme disease, ehrlichiosis, and anaplasmosis, three diseases that are transmitted by ticks.
Your veterinarian may also want to perform X-rays of the chest and abdomen, as well as ultrasonographic examination of the abdomen. Imaging helps to rule out cancer, which can cause Evans syndrome. By using an ultrasound machine to look at the abdomen, your veterinarian can also rule out free blood in the abdomen. In some cases, a bone marrow sample may be recommended to rule out specific cancers.
Treatment for Dogs with Evans Syndrome
Treatment for Evans syndrome will involve hospitalization with fluids, supportive care, and blood transfusions. Steroids, such as dexamethasone injections, are used in addition to other medications that modulate the immune system to halt the body’s attacks on its own cells.
If your dog has an infection, specific antibiotics will be started. Even if testing for tick-borne diseases is negative, some veterinarians may start your pet on doxycycline to cover all their bases.
A single low dose of the chemotherapy agent vincristine given into a vein has been shown to accelerate the return of appropriate platelet levels. This dose is too low to cause the typical side effects seen with chemotherapy agents but can be beneficial if your dog’s platelet levels are low enough to cause spontaneous bleeding.
With Evans syndrome, your dog may experience bleeding in their stomach and intestines. To prevent this or reduce the effects if it’s occurring, your veterinarian will start medications to reduce ulceration and coat the stomach and esophagus, such as omeprazole and sucralfate.
Evans syndrome also increases the likelihood of developing blood clots (thromboembolism). Because of this, your pet may be started on a medication like clopidogrel to reduce the likelihood of dangerous clot formation.
If your dog’s Evans syndrome is caused by an underlying cancer, treatments aimed at the cancer itself could include chemotherapy, surgery, radiation, and other disease-directed treatments.
In the most severe cases, the veterinarian may recommend plasma exchange or plasmapheresis. Your pet’s blood is circulated through a filter to allow their plasma to be cleaned of destructive circulating immune chemicals while preserving red blood cells and platelets. Donor plasma will be returned to the pet.
Evans Syndrome in Dogs Survival Rate
Evans syndrome is life-threatening and certainly more serious than either IMHA or IMTP on their own.
Dogs who survive the first few days after hospitalization and are discharged from the hospital generally have a good long-term prognosis.
Pets with secondary Evans syndrome have a variable prognosis depending on the underlying cause. For example, if the pet has cancer, their prognosis will depend specifically on that cancer, whereas a dog who developed Evans syndrome in response to a vaccination may have a better prognosis if they survive the initial illness and aren’t vaccinated in the future.
Some studies report that Evans syndrome has a mortality rate around 30 percent, while some hospitals report a less than 10 percent mortality rate. Around 40 percent of cases will experience recurrence or a relapse when medications are withdrawn, indicating the importance of long-term management of Evans syndrome in dogs. Survival depends heavily on treatability of the underlying cause and rapid initiation of treatment.
Long-Term Management of Evans Syndrome in Dogs
After your pet survives the onset of Evans syndrome, you’ll work with the veterinarian to determine a long-term management plan.
Many pets will need to be on immunosuppressants for life. The goal will be to reduce the medication to the lowest effective dose. It may take months and many follow-up appointments to achieve long-term control in severe and relapsing cases. Your veterinarian will likely plan a slow taper to find a good long-term dose. Tapering medications too soon or too rapidly can lead to relapse, which is often more severe than the initial onset of Evans syndrome.
Your veterinarian will likely advise against vaccinating your pet in the future, which may reduce your ability to do things like board your dog or see groomers. Your veterinarian may recommend titer testing to see if your pet continues to have protection against dangerous diseases that are typically prevented by vaccination.
Cost to Treat Evans Syndrome
Evans syndrome will require testing for diagnosis and multiple days of hospitalization on fluids, blood transfusions, and immunosuppressants. Although mild cases may be manageable for several thousand dollars, treating Evans syndrome can easily cost over $10,000.
If you are unsure about your ability to afford treatment, you could consider online fundraising or applying for CareCredit to help you pay for your dog’s treatment. Proactively getting pet health insurance can also help you to be covered should Evans syndrome arise.
You can also expect $150-$300 per month to manage the condition long-term. In secondary Evans syndrome, cost of management will depend on the underlying cost. For example, pursuing treatment for cancer will raise the cost significantly.
How to Prevent Evans Syndrome in Dogs
Given that most cases of Evans syndrome have an unknown cause, you cannot always prevent your pet from developing this life-threatening condition. However, there are steps you can take to reduce the risk of secondary Evans syndrome.
Keep your pet on tick prevention to reduce risk of transmission of tick-borne diseases that can lead to Evans syndrome. Consider requesting that your pet get tested for tick-borne diseases at their annual visits. The 4Dx SNAP test is typically run in-house, takes under 15 minutes, and only requires three drops of blood.
Make sure to get your pet their regular wellness exams. Your veterinarian may detect conditions like cancer that can cause Evans syndrome before your pet is symptomatic.
What about vaccinations? Your pet has a higher risk of becoming seriously ill from an infectious disease if they are unvaccinated than they do of developing Evans syndrome from a vaccination. If your pet has no history of Evans syndrome or other autoimmune conditions, vaccination is almost always safe and effective. If your pet does have a history of autoimmune conditions, you may choose to forego vaccinations. In this case, work with your veterinarian to reduce risk to your pet of contracting infectious diseases.
Lastly, because of the familial association of Evans syndrome, breeders should not breed dogs who have developed this condition.