Splenomegaly, or the enlargement of the spleen, is one of the biggest question marks in ferret medicine today. As a veterinary pathologist, over 15% of my surgical biopsies from ferrets involve enlarged spleens. As a ferret owner, I have seen the spleens of several of my ferrets wax and wane in size over the years. In truth, one of my ferrets, who is now seven, has had an enlarged spleen for most of his life.
Fact -- we don't know what causes splenomegaly in the ferret. There are several theories, and I have come to my own conclusions (which I'll discuss in a moment), but nobody really knows for sure. Remember, as compared to dogs and cats, we actually know very little about ferret disease. While our knowledge about this species grows daily, it will be many years before we amass the amount of knowledge about ferrets that we have about more traditional companion animals.
First of all, what does the spleen do? The spleen actually has several functions. Its most important function is to act as a filter for the blood, ever sifting the blood for bacterial agents or evidence of inflammation against which its high population of white blood cells may mount an attack. Additionally, the spleen may act as a storehouse for blood - in some species, the spleen holds as much as 15-20% of the total blood volume in reserve, so that it is immediately available in times of stress. Additionally, the spleen filters out old red blood cells, which are trapped and subsequently digested by the white blood cells that live there - the iron in these cells is reclaimed, and may be used again if necessary, or it may be stored in the spleen against future needs. Finally, the spleen, in many species, and especially in the ferret, is where new blood cells, of both the red and white varieties, may be made, in addition to the bone marrow. Generally, this process occurs only where there is a greater than normal need for these cells, (i.e., after hemorrhage, or during systemic infections.)
All this is fact. Here's another fact: only five percent of the enlarged spleens that I see in my pathology work are the result of some type of neoplasm - lymphosarcoma being the most common neoplastic cause of splenomegaly. By far, the most common cause of splenic enlargement in ferrets is an accumulation of massive numbers of developing red and white blood cells (known as "extramedullary hematopoiesis") .
What causes splenic hematopoiesis? Well, that's where the theories begin.
Certainly, all spleens with lymphosarcoma or any other type of neoplasm should come out immediately. Veterinarians can tell when a spleen has a neoplasm in it without taking it out - they can aspirate cells from it with a needle and light anesthesia, or take a small piece of it during exploratory abdominal surgery. Qualified veterinary pathologists with experience with ferrets can then look at the cells in the biopsy to determine whether they are compatible with lymphosarcoma, other neoplasms, or are more consistent with a proliferation of immature blood elements.
In situations where a neoplasm is not present, the pros and cons of splenectomy should be discussed with your veterinarian. If an animal simply has a large spleen, but shows no signs of illness or discomfort, it is safer for the animal to leave it in. However, if the animal shows signs of discomfort, such as lethargy and a poor appetite, or a decrease in activity, then the spleen may come out. Finally, if the spleen is especially large, and the animal is very active, there is a risk of splenic rupture, and once again, splenectomy should be considered.
As of yet, the jury's still out on big spleens in ferrets. However, we do know that all of these cases should be investigated by your veterinarian, and appropriate steps taken to insure your pet's health and well-being.
Bruce Williams, DVM
Dr. Williams is available to help with diagnoses and answer questions.
The vast majority of enlarged spleens are benign problems that do not threaten your ferret's health, however, about 5% overall can be due to tumors, the most common being lymphosarcoma.
95% of splenic enlargements are due to a massive proliferation of red and white blood cell precursors. This change is due to the presence of a chronic smoldering infection, the most common of which is gastric infection with a bacteria called Helicobacter mustelae (which almost every ferret has).
Usually, this problem is worked up by examining the animal and seeing if other signs of a chronic infection are present - bloodwork, and occasionally, an aspirate of the spleen itself with a needle, which can be examined under the microscope. That often gives you at least a preliminary diagnosis of hematopoiesis vs. lymphosarcoma.
I generally recommend splenic removal only if a) the animal has become lethargic due to the presence of the enlarged spleen, and b) an infection is not identified. Removal of the spleen in ferrets is a relatively simple operation, and they tolerate life without spleens better than any other type of animal....
Bruce Williams, DVM, DACVP
Dr. Williams is available to help with diagnoses and answer questions.
1. Splenomegaly is a very common finding in the ferret, especially in those over 3 years of age. It is not always possible to find a specific reason for the enlargement, and it indeed, may be a benign finding. Often the spleen is just congested or hyperplastic for unknown reasons. However, there are a number of diseases that are associated with splenomegaly and diagnostic tests should be performed to rule out these problems, the following is a list of diseases to be considered in a differential. [Many of the other diseases listed have their own FAQs.]
2. Causes for splenomegaly: Lymphosarcoma, insulinoma, cardiomyopathy, adrenal neoplasia, Aleutian disease, eosinophilic gastroenteritis, systemic mast cell neoplasia, hemangiosarcoma, splenitis, and hypersplenism.
3. Splenitis has been seen in our practice and responded to a splenectomy and antibiotic therapy. Hypersplenism is a "catch-all" term that refers to a condition that presents with a high fever, leukopenia, erythrocytopenia and depression. The condition responds to splenectomy and corticosteroid therapy at .50 - 2 mg/kg. Unknown etiology, but it is this author's guess that this may be early lymphosarcoma.
Although it is probably just benign changes in the spleen, very enlarged spleens can cause a variety of weird blood values and cause profound lethargy. I have had a few spiking fevers also. Treatment is to remove the spleen. I have done this in 1-2 cases where the ferrets were feverish with no complications. Other than that, the goal is supportive in nature and try to reduce the fever (either by tepid water baths or medications).
Although splenectomy is an abdominal surgery it is straightforward. When isoflurane is used for anesthesia the ferrets wake up quickly after surgery and can usually go home the same night (if surgery is performed early) or the next day. Post operatively we recommend limited activity for 7 days (don't encourage playing and separate the ferret that had surgery for at least 2-3 days). When the patient comes home it is usually best to feed him small amounts 3-4 times a day for the first day or two. Suture removal in 10-14 days. The potential complications include bleeding (usually within the first 24 hrs.) and infection (within first 48-72 hrs.). Warning signs indicating complications include gums that are pale (rather then pink), poor appetite, lethargy, swelling or inflammation at suture line.
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