VetInfo Digest April 2000
This Month:
Rumors and Fads in Veterinary Medicine
Changing Information Sources
Some Stuff I Know Even Less About Than Most Things
Neutrophil Functions and Disorders
I found it necessary in this issue to point out that I am a general practitioner, with a smaller than average small animal practice. For some reason, it seems to many people that I am an expert in one area of medicine or another and it is really important that people understand that this is simply not true.
Information access has changed since I have been in practice, though. Previously, it was hard for a rural veterinarian to keep up with current veterinary information. Travel expenses and journal fees made it hard to keep current. Then the Veterinary Information Network became a part of America Online and after that came the World Wide Web. A rural practitioner with a little time to learn to search the web could suddenly compete with almost any vet in obtaining current information. I latched on to this opportunity quickly and the result is www.vetinfo.com.
Last month I was asked to be the speaker at a continuing education seminar on computer use in veterinary practice. So finally, I might really be an expert in something! It just isn't a particular disease or species, it is computers and searching the Internet for information relating to pet health care, something most of you already understand.
Rumors and Fads in Veterinary Medicine
How do you know if your pet is just being treated for the latest "fad" in medicine? How do you know if the latest rumor about a deadly pet disease is real ?
Everyone has heard of urban rumors by now, probably. These are the stories that circulate quickly because they have enough truth in them to make people believe they might be totally true but they are dramatic enough to make people tell their friends and neighbors. An example is the doberman with the burglar's fingers stuck in his throat. Many people have heard this story but the exact location of where it occurred and who was involved is always pretty fuzzy.
There are lots of situations in veterinary medicine that seem to develop along the lines of urban rumors. Among these are rumors of special susceptibility to anesthetic death among many dog or cat breeds, the recent publicity over suspected toxicity of Fabreeze (tm) that was untrue and constant rumors of "new strains" of parvovirus causing severe outbreaks of this disease that might be coming to an area near you, soon.
In addition to rumors that circulate, there is a tendency among veterinarians and their clients to participate in fads in medical therapy. Since I have been in practice there have been a couple of really big fads. The first one was hypothyroidism. For a couple of years, almost anything that went wrong with a dog could be attributed to hypothyroidism and often was. This fad was supported by the lack of a really good test for hypothyroidism and by a tendency among dogs to develop nice haircoats when thyroxine is administered, whether they need it or not. Another popular fad was the diagnosis of Lyme disease. Considering the great difficulty in establishing this diagnosis, I am constantly amazed at the number of people who claim to have it and the number of pets who are treated for it, or vaccinated to protect from it, in areas of the country where the incidence is very low. It was awfully tempting to tell people their pet had Lyme disease when it was hard to come up with another diagnosis. Most clients were satisfied with this diagnosis and treatment is nonspecific enough that many of the pets managed to get better whether they actually had Lyme disease, or not. One of the current fads is the use of glucosamines and chondroitin for arthritic conditions. While there is a lot of anecdotal information supporting this use, there isn't really very much scientific data to back it up, despite several years of use. The safety of these products has made most veterinarians look past the efficacy issue and go ahead and recommend them. While this may turn out to be good medicine in the long run, right now I'd have to call it a fad, even though I am one of the vets that does recommend trying these products in many cases.
The flip side of this problem are the rumors that turn out to be true and the fads that turn out to look like good medicine even ten or fifteen years later. When the link between cat food diets deficient in taurine and cardiomyopathy was made, there were a lot of people who felt vindicated in their claims that cat food must be harming their cat. It seemed almost unbelievable when the first mention of tumors arising in cats at vaccination sites was made. But over time, it became apparent that this was a real phenomenon, even if it is relatively rare. Sight hounds really are more susceptible to barbituate anesthetic agents, even though most breeds with reported anesthetic sensitivities really don't have them. Rimadyl (tm) can cause death if patients are not carefully monitored and clients are not fully informed of this risk.
So how do you determine if your pet is being treated for the latest fad or if the big news about a new strain of flesh-eating bacteria on the Internet is for real?
Just about every vet hears the following statement sometime in veterinary school; "When you hear hoof beats, think horses, not zebras." What this means is that it is important to think about the probability of various conditions occurring and then decide if the latest worry really seems to apply to your pet. If you are doing this right, when the problem is likely, you are hearing hoof beats from horses. If it seems unlikely you are hearing hoof beats from zebras. This might also explain why you hear about zebras on "ER", sometimes!
Hypothyroidism is a good example to consider as an example of veterinary fad. In general, hypothyroidism is a disease of older dogs. When someone suggests that your two year old dog with skin disease might have this condition, they are probably wrong. Just going with the odds, an underlying cause like allergies or mite infestation is more likely. This person is hearing a zebra where there is probably a horse. If someone suggests that your ten year old dog with unexplained hair loss and moderate weight gain might have hypothyroidism, they are more likely to be right. They are going with the probability, or listening for horses instead of zebras. This does mean you have to do at least enough research to determine the basic probabilities for various diseases or problems you are hearing about. That is part of thinking these things, through. It is important to remember that both horse and zebras exist in the world, though. When the usual suspects aren't showing up in lab testing or when treatment for common conditions isn't working as anticipated, that is the time to remember that there are other, less common problems that could be occurring.
If a disease or disorder is receiving a lot of press, it is important to remember that it still only affects a portion of the population. Pay attention to the details of reports and learn what portion of the population is likely to be affected. Worry if your pet fits the profile of likely sufferers, but don't think that every disease that gets a lot of press is a risk for your pet. You can help prevent your pet from unnecessary treatment by being wary of fads in veterinary medicine.
When you hear rumors about problems with products or new diseases, the first question to ask the person reporting it to you is, "Do you personally know the person whose pet was affected by this product?", and the next question is "Do you remember the details of the problem?". If the answers are "It happened to a friend of a friend," or "it happened to some cat in the next county" and if the details are sketchy, don't ignore the warning but do take it with a grain of salt. Keep checking into the problem until you are satisfied that it is real or that it isn't. Being a skeptic is usually better for your pet's health when things don't sound entirely right.
A changing view on information sources
I know that we have devoted a portion of several issues of the VetInfo Digest to searching for information. However, every once in a while I notice a change in the way that questions are asked or in the information that subscribers are providing that makes me look for the reasons why.
Recently I have begun using the www.google.com search engine. I am finding that it gives me a little more accurate responses, although there are still a lot of links that aren't truly relevant to most of my searches. In addition to more accurate responses it seems to hit more links at educational facilities than the other search engines. It is possible to find the curriculum notes from many of the veterinary schools. While it is probably hard for nonmedical professionals to read some of these pages without a medical dictionary, the notes are often very current and well organized. To give you some idea of the level of detail is it possible to get, check out these two web addresses: (which I actually originally got from one of our subscribers, but did find easily with www.google.com)
www.vetmed.wisc.edu/dms/james/VMIIN.HTML
www.vetmed.wsu.edu/boeing/small_animal_medicine/dialysis.htm
You might want to check out these sites and learn to look for similar ones, if you need even more detail than we can provide, in your search for answers to your pet's health care problems. I'm sure that most of you realize this, but the "vetmed.XXX.edu" in the address is what you are looking for when trying to find a site from a veterinary school.
Also, don't forget to check out the PubMed web site when you really need to see an abstract of the original references on material related to veterinary (or human) medicine. Go to: www.ncbi.nih.gov/PubMed
What are my personal weaknesses?
For some reason, many people assume that I am an expert on one subject or another. There are a some diseases for which my expertise exceeds most veterinarian's but these are few and far between. Heartworm disease is a major problem in the area I practice in. I feel quite competent discussing heartworm disease even when I am attending seminars that are put on by experts in this field. For some reason, I seem to have a higher percentage of diabetic patients than many practices and I feel reasonable competent in this small area of medicine, as well. I like internal medicine and I do all the general surgery for a very small practice but I am just a general practitioner, not a specialist in either of these fields.
In practice I have a couple of obvious weaknesses. One is reading X-rays. I tend to see things that aren't there and to miss things that are there, despite trying to carefully and systematically read X-rays. For this reason, we do send more radiographs to radiologists for review than many practices. Fortunately, my wife, who is also a veterinarian, is better at reading X-rays than I am, so I do have a backup.
Behavioral problems are difficult for me to consult with clients about. Even though I spend a lot of time reading about behavioral medicine and have good references to review, I can't shake the feeling that there just isn't enough objectivity to this area of medicine, at the present time, and that recommendations that can be made are not really backed by scientific studies. In addition, there is a strong temptation to try for an easy fix since clients are often frustrated by the time they are willing to mention a problem. Pharmaceuticals are available for a limited number of behavioral problems but there isn't a lot of clinical data that supports or refutes their effectiveness. This is just a difficult area of medicine for a veterinarian who really likes to have strong supporting evidence for treatment methods. I will try to help with behavioral issues online and even in the VetInfo Digest but it is important that people recognize that I am reporting the consensus of opinion, based on reading literature about this field, not speaking from rich personal experience.
Another area of great difficulty for us is oncology, the study of causes and treatment of cancers. In this field of medicine the big problem is that there is a great deal of research going on all the time and much of it doesn't become public until long after it is completed. Trying to keep up in oncology without having the time or ability to attend seminars devoted solely to this topic on a regular basis is very difficult. Radiation therapy, chemotherapy and even surgical recommendations change fairly frequently. Often, by the time a chemotherapy protocol is published it has already been modified or replaced in the clinics whose veterinarians published the article.
In order to best attack many cancers, the ideal approach is to biopsy the tumor prior to attempting surgical removal. Once the biopsy report is available a plan for treatment is made using the information on the type of tumor and its estimated grade. It may be necessary to take chest X-rays to look for spread of the tumor, then have an MRI done to evaluate how much tissue the tumor occupies in the local area. An examination of regional lymph nodes, blood work and physical exam is done to try to determine how far the cancer may have spread. This process is referred to as staging the tumor. A tumor that has not spread beyond the tissue it originated from is usually referred to as Stage I. The rest of the staging varies according to the biological behaviors of particular tumors and staging criteria are sometimes different from one tumor to another. Surgery to remove the tumor is planned with all of this information in mind.
Finally, there is a decision on what sort of ancillary treatment to pursue. Chemotherapy is appropriate for some tumors and radiation therapy appropriate for others. The type of chemotherapeutic agent used is based on the type of cancer. Sometimes a single chemotherapeutic agent is quite effective against a tumor type and other times it is necessary to use multiple chemotherapy agents on a rotating basis, according to a set protocol. The mix of and timing of administration for chemotherapeutic agents that is most effective is hard to determine and consequently there are often significant differences in how chemotherapeutic agents are being used at the current time in oncology specialty practices and published information on chemotherapy.
All of this is quite costly and may produce benefits as limited as an additional two or three months of reasonably good quality life. Even when chemotherapeutic regimens work well, as is the case for lymphoma in dogs, there is still a chance that an individual dog won't respond well to therapy. It is hard to advise a client to spend two or three thousand dollars in these circumstances, but many clients do wish to have this option. It is hard to advise my on-line community when the standards of treatment change rapidly and when new information on survival rates may be published at any time. In our private practice we strongly advice our clients to seek the help of a board certified specialist in oncology whenever we have a patient for which this sort of advice seems necessary.
Surgery can be a little difficult to provide advice for online, since new surgical techniques are also developed and often used for some time prior to their inclusion in the literature. Keeping abreast of changes in surgical therapies also sometimes requires attendance at meetings where there is an emphasis on surgery. At the present time the areas of reconstructive surgery and orthopedic surgery seem to be changing more frequently than soft tissue surgery is. I don't actually view this as a big weakness in our practice but it can sometimes be a noticeable weakness online.
I would like to be able to provide knowledgeable first hand advice on all areas of medicine but that really isn't possible. When I feel that I am weak in an area of medicine I will try to let you know that in any replies or publications on a topic. Hopefully that will make it possible for you to understand why we sometimes make the recommendation to consult with a specialist rather than providing more detailed information ourselves and why you might want to heed that advice if you are hearing it from your veterinarian, too.
Neutrophils.
People often send us total white blood cell counts and ask what they mean. The truth is that the total white blood count by itself is often meaningless. The total count needs to be considered in light of the clinical symptoms the pet is experiencing and the counts of the individual white blood cells that make up the total.
The cell that usually makes up the majority of the white blood cell count is the neutrophil. It is becoming apparent that some of the diseases in which immune deficiency is a factor are occurring due to specific deficiencies in neutrophil function. It is likely that more and more of these diseases will be discovered over the next few years as the technology to recognize them improves.
It is necessary to understand how neutrophils are produced and how they are distributed within the circulation and within the body in order to understand the importance of neutrophil deficiencies, excesses and the consequences of poor neutrophil function. Neutrophils are formed in the bone marrow. They originate from a cell known as an hematopoetic stem cell. These undifferentiated cells develop into the precursors for neutrophils, eosinophils, basophils, monocytes, mast cells, red blood cells (erythrocytes) and platelets. This is an important point because drops in neutrophil production alone rarely, if ever, occur. When neutrophils are deficient there should also be a deficiency of other cells arising from the hematopoetic stem cells if the problem has been going on for any length of time. It is important when looking at cases in which it appears that there is a deficiency restricted to neutrophils to realize that this may be an early sign of a total failure of the bone marrow's ability to produce white blood cells.
It should also be noted that lymphocytes were not included in the list of cells produced by the bone marrow. While some lymphocyte production does occur there, the majority of lymphocyte production occurs in other organs, most notably the spleen, thymus, tonsils and lymph tissue in the gastrointestinal and respiratory systems. This is why lymphocyte counts may be unaffected by diseases that destroy the bone marrow's ability to produce other white blood cell lines.
Neutrophils are released from the bone marrow as they mature. In ordinary circumstances the bone marrow releases mostly "segmented" neutrophils, which are the mature form of this cell. When the demand for neutrophils increases due to infectious or inflammatory diseases, the bone marrow releases "band" neutrophils, which are nearly mature neutrophils. In times of severe need, the bone marrow may release even younger neutrophils, known as metamyelocytes, myelocytes or promyelocytes. When young neutrophils are released into the circulation the situation is referred to as a "left shift". A slight left shift indicates a strong need for neutrophils that the body is responding to but is not overwhelmed by. When the left shift is severe enough that metamyelocytes or even more juvenile neutrophils are being released into the circulation the body's ability to respond to a disease may be overwhelmed.
Neutrophils are the foot soldiers of the body's immune system army. They enter the circulation and live there for about ten hours before heading off into the tissues to do battle with foreign invaders. A neutrophil in the bloodstream follows the circulation until it comes into contact with the blood vessel lining. It is attracted to this lining and tends to roll along its surface for awhile until chemical signals from inflamed tissue make it stick to the wall and finally make its way into the tissue by actually dissolving a small portion of the blood vessel wall. Then it follows the chemical trail to do battle with whatever it encounters. Fortunately for the neutrophil, the antibody system often attacks its target first, making it easy to recognize and easier to kill. Bacterial and foreign substances are engulfed by the neutrophil then destroyed using enzyme systems that produce toxic oxygen radicals and hypochlorous acid (similar to dilute bleach). (Brooks and Catalfamo, Kirk's Current Therapy XII). Their total life span is probably no more than two days in most circumstances. Once a neutrophil makes it way into body tissues it does not return to the circulation in the future. Once a neutrophil completes its mission it is destroyed itself by monocytes. When large numbers of neutrophils and other white blood cells die in one spot, the resultant collection of dead white blood cells and debris is referred to as pus.
The pathway that neutrophils follow to get into the tissues leads to a confusing factor in neutrophil counts. There are actually four major groupings of neutrophils in the body, the neutrophils in production in the bone marrow, the neutrophils flowing freely in the circulation, the neutrophils that have already moved out of the free flow of circulation and are rolling along the blood vessel wall or are attached to it and the neutrophils already in the tissues. It is only possible to measure one group of these neutrophils by drawing a blood sample, the group that is freely moving within the circulation.
The group of neutrophils that are not moving freely but remain in the circulation can be looked at as a reserve army, or a marginal pool of neutrophils available in an emergency. In dogs, the marginalized neutrophils are roughly equal in number to the circulating ones. In cats, the marginalized neutrophils outnumber the circulating ones three to one. This would be no problem for veterinarians except that when there is strong tissue demand in one area of the body, the neutrophils that are still in the blood vessels but are not moving freely can change their mind and get back into the flowing circulation again. When this happens in cats, the result can be a very quick doubling of the neutrophil count. One of the reasons that this happens is stress, making blood cell counts drawn in the veterinary office from an unwilling cat subject to this effect. It is not unusual for a cat that is stressed to have an elevated total white blood cell count due to the strong increase in circulating neutrophils.
A decrease in the number of neutrophils in the circulation is referred to as a neutropenia. An increase in the number of neutrophils in the circulation is referred to as a neutrophilia. When there is a rise in neutrophil numbers and no increase in juvenile neutrophils in the blood stream, there is a strong presumption that the rise is due to release of the marginalized neutrophils and is due to stress, cortisone administration or an infectious or inflammatory process that is not creating a demand for more neutrophils than the body can supply. When there are immature neutrophils in the circulation and a rise in neutrophil count a "left shift" is occurring. When there are immature neutrophils and a normal or decreased neutrophil count a "degenerative left shift" has occurred. This usually indicates an infection that is really outstripping the body's ability to respond and is a bad prognostic sign.
There is an unusual neutrophil reaction that can occur, in which there is a big tissue demand for neutrophils which causes a rise in neutrophil numbers without a left shift due to the fact that the body can keep up with the demand. This usually occurs when infection is in a confined space such as the uterus or a kidney, is a response to cancer or when neutrophils in the body are not able to function properly so they are produced but do not enter the tissues for some reason.