Internal Medicine

Open 24/7 403.770.1340

Internists deal with the vast array of medical disorders that affect our pets. Cardiac disease, kidney disease, endocrine disease, gastrointestinal disease and respiratory disease are just a few examples. Most diseases are diagnosed through the acquisition of historical information, thorough physical examination, and specific diagnostic tests.

Our internal medicine specialists are:

  • Debby Henderson, DVM, BSc, Diplomate ACVIM
  • Chantal McMillan, DVM, BSc, Diplomate ACVIM
  • Serge Chalhoub, DVM, BSc, Diplomate ACVIM
  • Casey Gaunt, DVM, MVetSc, Diplomate ACVIM

Feline Leukemia Virus (FeLV) & Feline Immunodeficiency Virus (FIV)

Feline leukemia virus (FeLV) and feline immundeficiency virus (FIV) are two important contagious viral organisms that infect cats.  They affect the immune system and can cause increased susceptibility to many diseases and cancers (including lymphoma, squamous cell carcinoma, and several forms of leukemia).  FeLV infection is also associated with bone marrow disorders (anemia, myelodysplasia) and reproductive disorders.

Feline Leukemia Virus (FeLV)

Feline leukemia is transmitted both from cat to cat and from mother to offspring. The most common route of infection is through contact with infected body fluids (blood, saliva, etc.).   Cats exposed to these viruses may 1) be able to fight off the infection, 2) develop a hidden/latent infection, or 3) become infected and continuously infectious to other cats.  Those animals that have a latent infection cannot transmit FeLV to other cats unless stress or immunosuppression (such as the administration of steroids) places the virus back into circulation.   Outside the cat, the virus dies quickly in a dry environment.   The virus can survive twenty-four to forty-eight hours in a moist environment and so can potentially be transmitted to another cat by shared litter boxes and food dishes.
The screening test for FeLV infection is a blood test called an ELISA antigen test.  All positive tests should be confirmed with either the submission of another more specific test called an IFA test or by repeating the ELISA test in three to four months.   To confirm a negative test after exposure, an ELISA antigen test can be repeated in three months.  It is important to realize that cats with latent infection will test negative, but may still develop associated disorders later in life.

Vaccination does not interfere with testing

Feline Leukemia vaccinations have been available for many years.   The vaccine is not one hundred percent effective.  The vaccine has also been associated with the development of an aggressive cancer at the site of vaccination called fibrosarcoma.  The risk of vaccination should be weighed against the risk of exposure and infection.  If vaccination is to be performed, test before vaccinating, as there is no benefit to vaccinating a FeLV positive cat.

Feline Immunodeficiency Virus (FIV)

There are five different types of FIV:  A, B, C, D and E.  In the United States, most cats are infected with subtype A on the West Coast and B on the East Coast.  The most common mode of transmission is through saliva and bite wounds.  The majority of FIV-positive cats are outdoor males.  FIV survives outside the body for only a few minutes and is unlikely to be transmitted by shared litter boxes and food dishes.  Most infected cats will test positive within sixty (60) days after exposure.  Kittens can test positive due to maternal antibodies, but usually become negative later.  Kittens should be re-tested at six (6) months of age.
FIV infection is associated with neurologic disease, chronic renal failure, cancers (especially lymphoma and squamous cell carcinoma), stomatitis (mouth and gum disease), respiratory conditions, diarrhea, urinary disorders, and wasting syndromes.

Unlike the FeLV test, the FIV test is an antibody test instead of an antigen test.  The viral antigen levels in FIV infection are usually too low to detect.  Additionally, antibody levels wax and wane.  They can be detected as early as two (2) weeks after infection.  IFA and ELISA are used as the methods for the screening tests.  FIV negative cats are likely to be uninfected.  A Western blot test is the confirmatory test.  Annual FIV testing is recommended for at risk cats i.e., outdoor cats and those living with FIV positive cats.

An FIV vaccine is available.  It is a killed vaccine composed of subtype A & D.  It is reported to be eighty-two (82%) percent effective at preventing subtype A.   There are no data as to the efficacy against subtype B, which is the subtype found on the East Coast.  Vaccinated cats will test positive on all tests including Western Blot tests.  Vaccination cannot be differentiated from infection on the FIV antibody test.  Kittens from vaccinated queens can test positive until eight (8) weeks of age.  Only those at high risk should be considered for vaccination and they should be tested as negative before vaccination. Given that any vaccinated cat may potentially always subsequently test positive for FIV on all available tests, cats receiving an FIV vaccine should be microchipped or in some other way permanently identified just in case they roam or get lost and end up in an animal shelter which tests for FeLV/FIV!

Treatment for FIV and FeLV

Treatment for FIV and FELV positive cats typically targets the treatment of the secondary diseases and supporting the immune system.  Good nutrition and management are important components of therapy.  Immunodulators such as the staphylococcal protein A, Acemannan, and interferon alpha have been used with varying degrees of anecdotal success.  Antiviral drugs such as AZT are also available.  Only the antiviral drugs have clinical data to support their efficacy but unfortunately have been found to cause adverse side effects.

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Diabetes Mellitus

Diabetes mellitus is a common disorder of both cats and dogs. While the exact sequence of events leading to development of diabetes may be somewhat different, the signs of the disease and its treatment remain very similar for both species.

Diabetes mellitus, or sugar diabetes, is a hormone disorder which causes a persistent elevation of blood and urine sugar called glucose. Persistent glucose elevations induce the signs of the disorder, which are excess thirst and increased urination. Insulin therapy remains the most common and effective treatment for cats and dogs with diabetes mellitus. Insulin is a hormone normally produced by the body and released into the bloodstream to prevent elevations of blood and urine sugar. Insulin therapy involves the pet owner injecting the hormone under the skin with a needle and syringe once or twice daily. There is no form of insulin available that can be given by mouth or added to the pets food.

Important facts regarding diabetes mellitus in pets:

  • With few exceptions, diabetes mellitus is a permanent disorder which requires treatment for the rest of your pet’s life.
  • With proper treatment, diabetes can be effectively controlled over the normal lifespan of your pet. In addition to insulin therapy, effective treatment may include strict diet and exercise regimens, use of special diets, administration of oral hypoglycemic drugs and frequent followups with your veterinarian.
  • Left untreated, diabetes mellitus is fatal. Additionally, diabetes can cause cataracts, severe metabolic toxicity (ketoacidosis), nerve and muscle weakness, rapid weight loss, increased susceptibility to infection, and damage to the kidneys, eyes, and brain.

A close cooperative effort with your veterinarian is critical to successful regulation of your pet’s diabetes. The number of and length of visits to your veterinarian’s hospital and the annual costs of your pet’s health bills will increase. What your pet gains from this cooperative effort is good health with a minimally restrictive lifestyle and a normal lifespan. Treatment of a pet with diabetes is not easy and certainly not practical for every pet owner. However, the treatment is very rewarding and worthwhile if the time and effort required can be provided.

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Addison’s Disease

Addison’s disease is a condition that occurs when the adrenal glands stop producing hormones. The symptoms tend to be non-specific and may include lethargy, weakness, and gastrointestinal upset. It is common for the signs to wax and wane over a period of time before a diagnosis is made.

Some dogs with Addison’s disease are not diagnosed until they are critically ill (an Addisonian crisis). This life-threatening stage of the disease results in collapse and shock—it must be treated as an emergency.

There is no cure for Addison’s disease, but it can usually be treated with replacement hormones, giving the dog a normal life span and quality of life. It is diagnosed (and monitored, once treatment has begun) with blood tests. The drugs most commonly used to treat Addison’s disease are called prednisone, Florinef, and DOCP—a dog may require only one or a combination of these medications.

Most cases of Addison’s disease are diagnosed in middle-aged dogs (the median age of diagnosis is 4-5 years), although it has been reported in animals as young as 2 months and as old as 14 years. Female dogs are disproportionately affected (about 70% of cases), with sexually intact females at greatest risk and intact males at the lowest risk. About one third of cases are mixed-breed dogs, but there appears to be some breed predilection, with poodles, Portuguese water dogs, Great Danes, Leonbergers, German shepherds, and rottweilers among those thought to be predisposed.

The prognosis for dogs diagnosed with Addison’s disease is excellent as long as they are carefully managed. They can be expected to live out a normal life span with few if any limitations, but they do require life-long medication.

The typical signs of Addison’s disease are vague and non-specific and are often seen in other, more common disorders. They can also vary widely in severity. Affected dogs may show lethargy, anorexia, vomiting, diarrhea, weight loss, shaking/shivering, or excessive thirst and urination. A characteristic feature of Addison’s is that the signs tend to follow a waxing and waning course and improve dramatically when the animal is treated with fluids and/or steroids.

Additional clinical signs that your veterinarian may observe on physical examination include: poor body condition, weakness, dehydration, weak pulses, a slow heart rate, and blood in the stools. Blood work may indicate: anemia, electrolyte imbalances (i.e., elevated potassium, low sodium, and low chloride), low blood sugar, elevated calcium, acidosis, and elevation of liver and kidney values.

Approximately 35% of dogs with this disease present in what is known as Addisonian crisis; this is a true emergency and immediate treatment is required to save the dog’s life. These animals have the classic signs of shock: mental dullness, pale mucous membranes, weak pulses, and cold extremities. In addition, they have an abnormally slow heart rate due to elevated blood potassium levels.

Mechanisms and Causation

The adrenal glands are paired glands that sit near the kidneys. They are made up of two layers, an outer cortex and an inner medulla, that are structurally and functionally distinct. The cortex produces three types of hormone: mineralocorticoids, glucocorticoids, and androgens, which are collectively known as steroids. Addison’s disease occurs when the adrenal cortices are destroyed and the body loses its ability to produce these hormones; the medical term for it is hypoadrenocorticism. There may be no clinical signs of disease until 90% of the adrenal cortex has ceased to function.

It is not well understood what causes the destruction of the adrenal cortices. In most cases the cause is thought to be autoimmune (the result of an over-active immune system) or idiopathic (unknown). Rarely, there may be other causes, such as bleeding disorders, infectious disease, or metastatic cancer. Addison’s disease may also occur when a dog that has being treated for a long period of time with steroids is abruptly withdrawn from the medication or when a drug called Lysodren is given, however, this form of the disease is usually reversible (fewer than 2% of these cases are permanent).


While the clinical signs may strongly suggest Addison’s disease, it can be definitively diagnosed only by means of a blood test called an ACTH stimulation test. A baseline blood sample is drawn, then ACTH (a hormone that stimulates the adrenal glands) is given by injection and a second blood sample is taken 1-2 hours later. The blood samples are analyzed to determine the level of adrenal hormone present; if the dog has shown little or no response to the ACTH administration, the test confirms Addison’s disease.


If an animal presents in Addisonian crisis, shock (i.e., low blood pressure and low blood volume) poses an immediate threat to his life and must be treated before the underlying disease is addressed. The most critical aspect of the initial treatment is intravenous fluid replacement; this restores blood volume and pressure and also helps to correct some of the biochemical abnormalities. An ACTH stimulation test should also be conducted at this time—it can be done concurrently with the fluid therapy. Fluids are administered at a high rate (shock dose) for approximately the first hour, then lowered to a rate determined by individual needs once the dog’s heart rate, pulse quality, and attitude improve. The dog often will improve rapidly with fluid therapy. The heart rate and rhythm, electrolytes, and other parameters will begin to normalize over the next 12-24 hours. During this time the dog will also begin to be treated with injectable steroids. Most dogs that present to the clinic in a crisis will spend at least 24-48 hours in the hospital; the length of hospitalization will depend on the individual dog’s condition and response to therapy.

Maintenance treatment for Addisonian patients consists of life-long hormone replacement to compensate for the body’s inability to produce glucocorticoids and mineralocorticoids. For dogs that present in crisis, this treatment can begin once they are stable and able to take food and water by mouth—for the others, it begins as soon as they are diagnosed. Glucocorticoid replacement is accomplished with prednisone, given orally on a daily basis.

There are two options for mineralocorticoid replacement, an oral medication called fludrocortisone (Florinef) and an injectable one called DOCP (Percorten-V). Florinef is usually more expensive than DOCP. Florinef must be given daily, and it has some glucocorticoid activity in addition to its mineralocorticoid activity, so dogs that take it may or may not need to take prednisone as well (about 50% of dogs will need prednisone). It is not unusual for a dog’s Florinef dose to rise gradually over the first 2 years or so of treatment, but it usually stabilizes after that. DOCP injections are given approximately every 25 days, but DOCP has exclusively mineralocorticoid activity, so dogs that take this drug will usually require daily prednisone as well. The response to DOCP is variable, so the actual dosing schedule must be tailored to the individual dog.

Stressful situations (e.g., travel, hospitalization, surgery) increase the body’s need for glucocorticoids, so you should keep a small supply of prednisone on hand to use as needed (your veterinarian will advise you on the appropriate dose for your dog).

Your veterinarian will recommend a specific monitoring plan for your dog, but typically it will include blood work every 5-7 days until the electrolytes have stabilized in the normal range (or for the first month if you are using DOCP), then monthly (or at the time of each subsequent DOCP injection) for the next 6 months and every 3-6 months thereafter.

An Addisonian dog needs to be carefully managed and faithfully medicated for the rest of his life, but as long as you do this, his prognosis is excellent for a normal lifespan and quality of life.

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Feline Hyperthyroidism

What is feline hyperthyroidism?

Hyperthyroidism is one of the most common disease diagnosed in cats eight years of age or older. In 95-97% of cats, the hyperthyroid condition is due to a benign (not cancerous) tumour of the thyroid gland. Only about 3% of cats have a malignant tumour causing their disease.

Symptoms of hyperthyroidism vary between cats; however, the most common signs are weight loss, increased appetite, failure to groom and an increase in water consumption, urination and activity. Some cats may also become aggressive and irritiable.

Why should hyperthyroidism be treated?

Hyperthyroid cats that are not treated usually become progressively more ill. Aside from the weight loss and the decreased quality of life through muscle deterioration, the excess thyroid hormone can cause elevated blood pressure, which may strain the heart and damage organs such as the kidneys.

Because hyperthyroid cats tend to be older, and some of their symptoms can also be compatible with other disease processes, complete laboratory testing is recommended to help diagnose any concurrent disease processes.

How is hyperthyroidism treated?

There are four treatments available for hyperthyroidism and each has advantages and disadvantages:

  1. Medical therapy with methimazole (also known as Tapazole) – This is an oral or transdermal medication that is readily available and is very effective in controlling the hyperthyroid state. Disadvantages include that it must be administered twice daily for the rest of your cat’s life, frequent monitoring with blood tests is required at least initially, 15-20% of cats develop vomiting and diarrhea or an itchy, scabby face and other side effects such as liver and bone marrow toxicity can occur.
  2. Surgical removal of the thyroid gland – This surgery is not difficult and does not require special equipment. However, hyperthyroid cats tend to be geriatric and may have other diseases that make them unstable patients for anesthesia and surgery. Additionally, the surgery can damage the parathyroid glands that are responsible for calcium regulation and serious calcium abnormalities can occur.
  3. Hill’s PrescriptionY/D diet – This is an iodine free diet. Because thyroid hormone is made of iodine, giving an iodine deficient diet causes a deficiency of iodine so the thyroid hormone cannot be made. Only this diet is fed to the hyperthyroid cat. No other food, treats or even some medications can be given because if these other items contain iodine, thyroid hormone production can begin again. It can also be difficult to use this food in a multi-cat house hold; non-hyperthyroid cats need supplementation with at least 2 tablespoons of other food per day. Monitoring by blood and urine tests is also required during the first few months of feeding this diet.
  4. Radioactive iodine therapy – This treatment requires only one injection of radioactive iodine, it resolves hyperthyroidism quickly, it does not require anesthesia, generally no medication is needed after therapy and it targets all thyroid tissue in the body. It does not damage the normal part of the thyroid gland or the parathyroid glands. It is definitive therapy. The disadvantage of this treatment is that it requires 7 days of hospitalization in radioactive isolation.

What tests are needed prior to radioactive iodine treatment?

Prior to scheduling a consultation to discuss radioactive iodine therapy, your family veterinarian will send a referral form and recent laboratory and examination results to us. Most cats will have had a complete blood count, biochemical profile, thyroid level and urinalysis performed before they are referred and these are the results we need. Many cats will have been treated with either the Y/D diet or methimazole and have had repeat laboratory tests repeated. We also need these results.

What happens at the initial consultation?

Based on the initial consultation, additional tests may be recommended prior to I 131 therapy. These may include an abdominal ultrasound, chest radiographs, blood pressure measurement, additional laboratory tests and sometimes, a cardiac ultrasound.During the initial consultation, Dr. Henderson will examine your cat, the laboratory results and discuss specifics of the radioactive iodine therapy with you. This consult usually occurs a week or two before the actual treatment; however, if you live out of the Calgary area, the consultation can occur the same day as the treatment, if special arrangements are made with Dr. Henderson.

The kidneys and the thyroid gland-what is the connection?

You may have read or your veterinarian may have discussed with you that treating the hyperthyroidism (with any of the available treatments referred to above) may unmask renal insufficiency. The reason is that there is increased blood flow to the kidneys caused by the hyperthyroidism. When the thyroid function normalizes, the blood flow normalizies and if the kidneys were depending on this increased flow to function properly, dysfunction can result. To test this theory, many cats are treated with a methimazole or Y/D trial and then blood tests are reevaluated to determine if the kidney function is stable once the thyroid is controlled. If the kidneys are stable, then these cats are good candidates for radioactive iodine therapy. If the kidneys are unstable, then your family veterinarian can discuss with you how best to manage your cat’s hyperthyroidism.

If your cat cannot tolerate methimazole and the Y/D diet is ineffective, radioactive iodine therapy can still be performed. We will be glad to discuss this situation with you; please have you family veterinarian send a referral form and all the previous laboratory reports to us.

What happens during the treatment with radioactive iodine?

After admission to the hospital, your cat is housed in the Nuclear Medicine Isolation Ward. We prefer to feed the usual diet and we do not have that diet in our hospital, we ask you to supply it.

A small towel or bed and a toy or two can also stay with your cat but these items will become contaminated with radiation and we cannot return them to you.

We have a TV in the isolation room and we play cat friendly videos. There is also a window which provided natural light. This room houses only 4 cats and there are no dogs present. Each cat is visible via web cam so that you can see your kitty anytime you want.

A single injection of radioactive iodine (about the same amount as a vaccination) is given under the skin. Sometimes, we shave a small area so that we can be sure the needle goes under the skin. After the initial injection, there is no other treatment-we have to wait to send these patients home until they have been with us 7 days and their radiation level is lower than or equal the release criteria set by the Canadian Nuclear Safety Commission.

While your cat is in radioactive isolation, we can change the litter box and give fresh food and water once daily. We cannot remain in the room (due to the radiation level) for longer periods. If your cat becomes ill during confinement, we are not allowed to take him/her out of radioactive isolation until the radiation reading is low enough and 7 days since treatment has elapsed.

Due to Canadian Nuclear Safety Commission regulations, you cannot visit your cat during the period of confinement.

What happens after the treatment?

Once the radiation level is appropriate and your cat has been in isolation for 7 days, he/she will be discharged. There are some simple rules for handling your cat and his/her urine and feces and we will give written instructions regarding this before the treatment so that if you have any questions, you can ask before discharge. The amount of radiation remaining in your cat does not pose a health risk to you.

If your kitty is doing well, no rechecks are needed for one month. At that time, a recheck should be scheduled at your regular veterinarian and blood and urine tests as well as physical examination will be performed. Don’t worry about the test details as we will send a letter to you regular veterinarian detailing what is required.

About 97% of all cats treated with a single injection of radioactive iodine respond to therapy. However, about 3% of these cats may need temporary or sometimes, permanent, thyroid supplementation because they can become hypothyroid. The follow up tests your veterinarian performs will help us determine if supplementation is needed.

Referral information for Radioactive Iodine Therapy

The diagnosis of hyperthyroidism is usually straightforward with a total T4 and routine laboratory tests. If clinical signs and initial laboratory results support a diagnosis of hyperthyroidism and the T4 is normal, then a Free T4 could be performed for confirmation. Pre-treatment tests should include a CBC, biochemical profile, T4 and full urinalysis collected via cystocentesis. These tests should be performed through a reference laboratory.

Once a diagnosis of hyperthyroidism is established, a methimazole trial (starting dose 1.25 mg q 12 hours) or Y/D trial is recommended to help predict renal function once the euthyroid state is attained. The above mentioned tests should be repeated after 2-4 weeks of methimazole therapy or after 1 month of Y/D therapy. If the T4 is normal and renal function is maintained, these cats are good patients for I 131 therapy and can be referred at this time. If initial physical examination reveals a fragile patient, then the therapeutic trial might be continued while the cat gains weight and becomes more stable for radioactive isolation.

Once the repeat laboratory tests are repeated as detailed above, please send a referral form and all laboratory results to WVSEC. We will call the client and set up a consultation with Dr. Henderson at that time. If needed, based on the initial consultation, additional testing such as thoracic radiographs, blood pressure measurement or cardiac ultrasound may be considered.

We generally treat cats with radioactive iodine every Wednesday, but will discuss timing of treatment with the owner at the initial consultation.

We strive to keep you informed of your patients and will send a referral letter and updates as necessary. However, if you have any questions, please do not hesitate to call (403-770-1340).