IMHA in dogs – how treatable is it really?

If your vet has diagnosed your dog with IMHA, or is considering a diagnosis of IMHA, you will likely be feeling very worried about what this disease with lots of complicated language is all about. This article aims to give an overview of the disease so that you can make the best treatment decisions for you and your pet.

What is IMHA and how serious is it?

IMHA stands for

Immune-Mediated (meaning the body’s own defences are what is causing damage)

Haemolytic (meaning breakdown of red blood cells)

Anaemia (meaning a reduced number of red blood cells in the body)

…in short, the body is attacking its own red blood cells, breaking them down in increased numbers and leading to a reduced ability to carry vital oxygen around the body, and overloading the body with the waste products from this process.

It is a serious disease, especially if it comes on quickly. It is treatable in many cases, but needs rapid veterinary input to give the best chance of survival, and left untreated it is fatal.

In 60-75% of cases, IMHA is classed as primary, meaning there is no cause other than the immune system over-reacting of its own accord. There is no known genetic link for this disease, but we know that Cocker spaniels, Springer spaniels, Irish setters, Poodles, Collies and Old English Sheepdogs are more likely to develop the disease than other breeds.

The other 35-40% of cases are secondary, meaning that there is an underlying cause. These are more commonly related to certain types of cancer, but also seen with drug reactions, blood transfusion reactions and some types of parasite that live in red blood cells. Parasites are considered a very rare cause in the UK, but with more dogs being imported from abroad, vets are having to consider this more often.

What is happening in my dog’s body if they have IMHA?

Red blood cells are produced in the bone marrow, and have a natural lifespan which ends when they become too stiff to move through the tiniest blood vessels. The recycling of old red blood cells is carried out by the spleen, liver and bone marrow, which recognise a protein on the cells surface which marks it out for destruction. When this happens, the iron inside the cells is sent to the liver in the form of bilirubin, which is yellow, and the proteins are broken down to be used again. Some red blood cells do not have the marker on them, and simply burst inside the blood cells when their useful life is over.

In IMHA, too many red blood cells are marked for removal. This leads to:

anaemia (too few red blood cells) and the body cannot carry enough oxygen around the body.

the oxygen carrying protein haemoglobin just floats around the bloodstream, which can cause damage to the kidneys.

the liver is overwhelmed by all the extra work it is being given to do, so the yellow bilirubin builds up, causing jaundice.

the protein markers on the outside of the red blood cells activates the complement system, which can rupture red blood cells in the blood vessels without needing to take them to the liver.

This cascade of events ultimately leads to the body’s clotting systems malfunctioning, and life threatening blood clots can form in the blood vessels

What signs might I see if my dog has IMHA?

Not all dogs show all signs in IMHA, and signs vary from mild to obviously an emergency, but be concerned if your dog:

Looks Pale

If you lift up your dogs lip, the tissues, tongue and gums should be a nice salmon pink colour. If they appear paler than usual or white, they do not have enough oxygen in their blood.

Is lethargic

Without the oxygen they need, your dog will be sluggish and sleepy.

Is breathing faster than normal and their heart is beating faster

This is their body trying to make up for the lack of oxygen.

Is looking yellow

Jaundice (or icterus as vets say) is when the gums, skin and whites of the eyes all appear yellow from too much bilirubin. IMHA is not the only cause of this. It can vary from very subtle to bright neon yellow.

Very yellow or deep red coloured urine

This is due to the increased bilirubin broken down either inside the tissues or inside the blood vessels.

What will my vet be looking out for?

There are other signs that your vet might find when they examine your dog:

Heart Murmur

If the heart sounds are ‘whooshing’ rather than clear, it might be a sign of anaemia; although this is also associated with many other conditions, especially heart disease.

Bruising of the gums and skin

If your dog’s platelets (a type of clotting cell) are also being destroyed (something called Evans Syndrome when seen together with IMHA), then they may develop bruises, anywhere from tiny pin pricks to large splodges.

Breathing difficulty, odd behaviour, pain in a leg, cold legs

These symptoms are signs of blood clots and mean the disease is at an advanced stage

What will my vet do if they think my dog has IMHA?

Your history and their examination will give your vet a good idea as to if they suspect IMHA, and they will want to take action quickly.

The first step will always be blood tests, where they can look for the numbers of red blood cells, any signs that the body is trying to replace those cells, any signs of infection, and to see how the liver and kidneys are coping. These tests can be done on the same day in most modern veterinary practices.

Your vet may also want to perform an in-house test on the blood sample called the saline agglutination test, where they mix the sample with salt water and then use a microscope to look for any clots that form – sometimes you do not need the microscope at all!

A urine sample can be useful to see if there is any free blood or haemoglobin in it.

Your vet may also want to send a sample to an external laboratory for a Coombs test (which looks for the protein marker on the red blood cell surface), or flow cytometry, which can assess just how much of the protein marker there is in the blood (which can be useful for monitoring treatment).

If your vet is suspicious of a secondary cause, imaging such as X-rays, ultrasound scans or CT scans may be recommended, as the treatment may be different for primary and secondary IMHA.

What treatments are available for IMHA and how successful are they?

Treatment of IMHA focuses on reducing the over-active immune response with immunosuppresants. In the first instance this is usually high dose steroids (given by injection and then by mouth), but if these are not effective quickly enough or on their own, your vet may use other immunosuppressant drugs such as mycophenolate, cyclosporine and azathioprine. All of these drugs should be handled with care by humans (especially those with a weak immune system) and do come with side effects, but treatment of IMHA without them is impossible.

If your dog is very weak, they may need hospitalisation for supportive care, including intra-venous fluids, oxygen, and maybe even a blood transfusion. All vets can provide fluid therapy, not all will be able to do a blood transfusion. In both cases, overnight care will be required for careful monitoring of your dog, and you may be sent to an out-of-hours centre for this.

Other medications such as anti-clotting drugs and ones that protect the stomach and intestines may also be needed to protect your dog from other effects of both the disease and the medications needed to treat it.

What is the long term prognosis for my dog if they have IMHA?

There is a very wide range of reported survival rates for IMHA, all depending on how sick they were when they first got to the vets and how well they responded to treatment. The faster the disease comes on, the more serious it usually is, and if they have developed signs of clotting problems the prognosis is much worse as damage has already been done to multiple organs.

Treatment needs to be prompt and aggressive, and even with a good response will need to be carried on for several weeks before being gradually reduced. Fatalities are often seen when treatment is stopped too soon or reduced too quickly, and the IMHA comes back.

With dogs that survive, recurrence of the condition is reported at 11-15% (meaning that for every 100 dogs with the condition that survive, 11-15 of them will be seen with signs again in the future).

Summary

IMHA is a serious disease in dogs that can have impacts on many systems in the body, and left untreated is fatal. Diagnosis in practice can be reasonably straightforward but may require referral for additional tests, supportive hospitalisation and more specialist care such as blood transfusions. Prompt treatment and milder signs can lead to a good outcome, but owners should be aware that treatment can be lengthy and will require multiple repeat blood tests to monitor response, which will increase the costs involved.