I have been asked to write a little bit about a condition called polycythemia. This is a condition of red blood cells. If we break down the word we can find the definition of the condition.
Poly = Many
Cyt = Cell
Heme = blood.
Literally polycythemia is a condition in which there are too many red blood cells (RBCs) circulating through the body.
Now, you may ask, why is this a bad thing? Blood cells are good, right? They carry nutrients and oxygen to other cells in our body so why is it bad to have too many?
Although the normal number of blood cells can vary based on geographic location and breed, normally this number is around 30-50% of the total blood volume. At this number, the blood is still thin enough to move through the tissues easily and to allow the cells to provide the appropriate nutrients and oxygen. However, if the number of red blood cells increase, the blood actually becomes thicker and this can make it difficult for it to get to the appropriate tissues to do its job. Think of it like this. If you pour milk onto a sponge, the milk quickly penetrates the pores of the sponge. The sponge is like your tissues and the milk, like normal blood. On the other hand, what happens if you pour maple syrup onto a sponge? It takes longer for the syrup to penetrate the whole sponge, if it does at all. The syrup is like blood with extra cells in it. The blood cells cant get to where they are needed and this affects the tissues of the body. The heart, lungs, circulatory system, nervous system and kidneys being hardest hit. The signs that we see when this disease is present are dependent on the underlying cause of the condition as well as the severity.
So, what does cause this condition and how do we determine the cause?
1. The most common cause of polycythemia is dehydration, or a decrease in the amount of fluid in proportion to the red cells. This can be the result of not consuming enough water, or by losing water through diarrhea, vomiting, or loss of fluid through malfunctioning kidneys or into other tissues. Rehydration will correct the polycythemia.
Some of the signs we might see in this instance include:
a) Dehydration from vomiting and diarrhea
b) Changes in behavior such as weakness and lethargy
- Red gums and skin
e) Abnormal bleeding, such as nosebleeds
f) Enlarged blood vessels
g) Difficulty breathing
h) Heart abnormalities
2. Sometimes the polycythemia is temporary and brought on by anxiety, stress, or seizures. In the instance, once the stressor is removed, the polycythemia will resolve.
3. There is a rare disorder of the bone marrow which can also produce polycythemia. (Polycythemia Rubra Vera). This occurs when the bone marrow produces too many red blood cells in an orderly fashion. In this instance the signs that might be seen include
a) Enlarged spleen or liver
- Blood clots
- Occasional seizures
If another disease process restricts oxygen to the tissues the body may compensate by producing more red blood cells to keep up with the demand for oxygen. When this occurs we will see signs related to the underlying cause.
Some of these disease process include:
- Chronic lung or heart disease
- Defective hemoglobin (the component of the blood which carries the blood)
- Brachycephalic breeds (Breeds with very short noses)
- High Altitudes
- Kidney mass
- Hormonal diseases.
Now we know that Polycythemia means that there are too many circulating red blood cells and we know some of the causes of this condition. How exactly does your veterinarian diagnose this condition in your pet and how does she know what is causing the increase in red blood cells?
If your pet is showing any of the above symptoms it is very likely that your veterinarian will want to run some blood tests. Blood is divided into two main portions. The fluid portion and the cellular portion. A CBC or complete blood count, looks at all of the cells in the blood. With this test we can tell what percentage of the blood consists of cells and what percentage is liquid. If the percentage of cells is greater than expected we call that polycythemia. We also look at the cells to see if the cells are young or old, large or small or if there appears to be a problem with the hemoglobin.
We also test the blood to see what the total protein level is in the blood. If the protein is also high than it is likely that the fluid portion of the blood is actually low, rather than an absolute increase in the RBC. This leads us to the most common diagnosis of dehydration and we look to diagnose and treat causes of dehydration.
If the total protein levels are normal than we need to keep looking.
Next we test the oxygen saturation, or how much oxygen is present in the blood. If it is low than we are concerned about those conditions listed in number 4 above. These conditions can rob the tissues of much needed oxygen. When the body realizes that it needs more oxygen it will produce a hormone called erythropoieten, or EPO. This hormone is essential in the production of red blood cells. When it is increased the body produces more RBC. So we can also test EPO levels to help us with a diagnosis of polycythemia. If EPO is elevated, your veterinarian should look for another cause of polycythemia such as heart or lung disease, cancer, hormonal disease etc. Other tests such as x-rays, ultrasound, a bone marrow biopsy and chemical tests on the blood will need to be performed.
If the total protein levels, oxygen saturation and EPO levels are normal and no other cause is isolated we likely have a Primary Polycythemia, known as polycythemia vera. The bone marrow biopsy will also help us come to this diagnosis.
Now that we have a diagnosis what do we do to treat it?
If you have read this far you can see that this is somewhat of a complicated condition with many different causes and factors. Since so many things can result in this condition it is important to come to the correct diagnosis and treat the underlying cause if one exists. If dehydration is the cause your pet will need to be hospitalized on intravenous fluids with specific chemicals called electrolytes to return his hydration to normal. The underlying cause of the dehydration will also need to be addressed.
All other causes of low oxygen levels will also need to be treated.
If dehydration is not the cause, a phlebotomy or blood letting will need to be performed. Some blood will need to be removed and replaced with special medical fluids. This needs to be performed carefully so as not to decrease the blood, oxygen or hydration levels too much or too quickly.
If the cause is polycythemia vera then a chemotherapy drug is indicated as well as the phlebotomy. This drug will help to decrease the excess production of red blood cells. Oxygen therapy may also be needed. During treatment your pet will need to be kept quiet and avoid exercise.
Your pet has been diagnosed and treated in the hospital and now its time to come home. Is everything back to normal or do you need to take some special precautions at home?
If the cause of the polycythemia has not been eliminated, it is possible for it to recur.
Therefore, it is important that you continue to watch your pet closely at home.
In addition to watching for signs of the underlying disease you will want to watch for any signs of:
- Difficulty Breathing
- Bleeding Episodes
- Changes in appetite
- Any signs of infection.
Your pet will also need continued monitoring by your veterinarian to assess progression of the disease as well as any side effects of the medications. This monitoring will likely include:
1. A physical examination
3. Platelet counts
4. Biochemical blood tests, and
5. Iron levels.
These tests will likely be more frequent in the beginning and then as your pet becomes more stable the frequency of these tests may decrease.
The Prognosis or expected outcome of polycythemia varies depending on the cause. Detecting and treating the primary cause of polycythemia will result in a better prognosis. It is best to discuss your individual pets prognosis with your veterinarian as they know your pet and its circumstances best.