IMHA – a common cause of anemia in dogs
IMHA is a serious and life threatening condition that affects both dogs and cats. IMHA stands for Immune Mediated Hemolytic Anemia. In essence, this means that your pet’s immune system, which typically fights of invaders and infections, is now fighting your pet’s own red blood cells. This results in the red blood cells being destroyed, causing anemia, as well as inflammation (damage) around your pet’s whole body.
IMHA is a disease that has been reported in small animals for over 80 years and unfortunately as yet, we do not have a perfect treatment for the condition. Nevertheless, there are now many newer drugs and treatment options for your pet, which means that they have a much better chance of survival than they used to. With careful treatment, up to 75% of dogs with IMHA can make a full recovery and go on to lead a normal life.
Symptoms of IMHA
Signs of IMHA may include collapse, weakness, increased breathing rate, yellow or pale gums. Some dogs will present with red or black urine. Many dogs have a fever, and most feel unwell, with a poor appetite or even vomiting.
How do you diagnose IMHA?
Diagnosis is usually straightforward – your vet will often notice the tell-tale signs on physical examination and recommend a blood test. This is usually called a “PCV” (Packed Cell Volume) which gives you a quick count of your dog’s red blood cells, reported as a percentage. Normal is between 35 and 55%, anything less than 35 means that your dog is anemic. If your dog is anemic, your vet will usually recommend follow up blood tests to determine why your dog is anemic. There are several classic signs that can be seen on a blood test that can confirm IMHA although occasionally additional tests need to be performed to ensure that the diagnosis is correct.
Why does my dog have IMHA?
In many cases, we cannot explain why a dog has developed IMHA. There may be some trigger (such as a virus) that has long gone, but has disturbed the immune system and caused the disease. However, we usually recommend that dogs diagnosed with IMHA have screening tests performed to look for a trigger, such as cancer, infection, or ingestion of toxins, as treatment of the trigger may resolve the disease. Some drugs can trigger IMHA, and there is a suggestion that vaccines could cause IMHA although many studies have failed to prove this. Your vet may recommend that x-ray or ultrasound tests are performed to try to look for an underlying cause, especially if your dog is older.
How do you treat IMHA?
Treatment for IMHA has evolved over the years and we now have many more options available.
The traditional, and first line medication is prednisolone (or dexamethasone). This is a steroid that quickly suppresses the inflammation and the immune-system’s attack on the red blood cells. Steroids do have side effects when used for long periods of time at high doses, so this medication is typically tapered over 3-6 months as your dog recovers.
Other drugs are often used to help treat IMHA or to reduce their dependence on steroids. These are drugs that are typically used to suppress the immune system, such as those used after a transplant in humans. They include Cyclosporine, Azathioprine and Mycophenolate. These are all oral medications (tablets or capsules) that can be given both in hospital and at home. They are usually well tolerated by dogs, although some monitoring is required to ensure that they are not causing any side effects.
Most dogs with IMHA require at least 1 blood transfusion, and many require two or more. Each blood transfusion has to be appropriate for your dog’s particular blood type and carefully administered over 4 hours to prevent transfusion reactions. While there are risks associated with blood transfusions, they are only used when absolutely required and can be life-saving. We obtain blood from healthy donor dogs; it is typically concentrated into “Packed Red Cells” to ensure that your dog gets the blood it needs as quickly and safely as possible. At VRH we have blood stored on-site ready to be given to your dog as soon as required.
Blood clot prevention
A common and often fatal complication of IMHA is the formation of blood clots. Dogs with IMHA have sticky blood that tends to clump together and form blood clots, or “thrombi”. These can travel to the lungs, brain, or other blood vessels and block blood flow. Prevention of blood clots has been one of the biggest improvements in treatment of IMHA over the past 10 years, with anti-coagulant therapy (blood thinners) being standard practice now. While it is still hard to completely prevent blood clots, we now have many newer injectable and oral medications that can be used such as “Clexane” (an injection), “Plavix” or “Xarelto” (tablets). These medications are usually used in hospital and may also be given at home during your dog’s recovery.
Newer or alternative treatments
Other treatments that have been tried for IMHA include IV infusions of human antibodies (Known as IVIgG) which help block the immune-system attack. This is unfortunately very expensive and can be hard to obtain as it is preferentially used for humans. Its efficacy is variable between dogs.
“Plasmapheresis “ is a treatment that has been around for many years but is experiencing a resurgance in popularity for IMHA in dogs. Recent articles have shown effective removal of the attacking antibodies and resolution of agglutination with the treatment. Access to plasmapheresis is limited currently, however in the future hopefully this will be more readily available for pets.
“Splenectomy” is a treatment commonly used in humans with IMHA. The spleen is an organ in the abdomen that helps “clean” the blood, and is involved in destroying damaged red blood cells in IMHA. Removing the spleen can help slow down the removal of red blood cells. It is not routinely used in dogs with IMHA unless they have failed more traditional treatments, or they have a problem found in their spleen on ultrasound.
Dogs with IMHA are usually very sick and require around-the-clock monitoring and support. Some dogs require IV fluids (a “drip”) to keep them hydrated and others require additional oxygen support. Our ICU can provide all these supportive treatments to your dog while they recover from IMHA. We may also give them pain relief or anti-nausea medications to help keep them comfortable.
How long does it take to treat IMHA?
Most dogs with IMHA require hospitalization for around 5 days. Some may respond sooner, and some will require up to 2 weeks of hospitalization depending on whether they have complications or require multiple blood transfusions. It can be a worrying time for you and we keep you frequently updated and informed as to the progress your pet is making. We encourage owners to visit and spend time with their pets while they are in hospital to help improve their pet’s morale and reduce stress. Once your pet’s red blood cell count has stabilized and started to increase, we will send your pet home, as long as they are eating and able to take medications. Your pet will be sent home with medications for you to give. These medications will be discontinued gradually over time, usually over a 3-6 month period.
Follow up checks are required which involve examining your dog and performing blood tests. This ensures that your dog is recovering as expected without side effects from medications.
While IMHA can be a serious disease, many dogs go on to make a full recovery and return to a normal quality of life, making it a very rewarding disease to treat.