| Addison's Disease (Hypoadrenocorticism) |
| Feline Hyperthyroidism |
| Feline Immunodeficiency Virus |
| Mast Cell Tumors |
| Tylenol (Acetominophen) Poisoning |
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Mast Cell Tumors in Dogs and Cats
Very few tumors present in such a wide variety of clinical signs: they are indeed the great impostors! They can look like anything and behave differently depending on the histologic type, location and the extent of the disease. The following is a brief discussion about these tumors. Some highlights are as follows: Mast cell tumor granules do not stain well with Diff Quick type stains unless they are "soaked" in the alcohol for several minutes prior to staining. Some important prognostic indicators include duration of presence, location and histologic type in the dog. Mast cell tumors tend to metastasize to nodes, liver spleen and bone marrow ...rarely to lungs. Radiation therapy is extremely effective for controlling local disease. Prednisone and vincristine when used as single agents induce a remission (partial or complete) in about 23% of the tumors. Vinblastine and prednisone appear to be effective. HISTORY AND CLINICAL SIGNS Mast cell tumors may exist in cutaneous or extracutaneous locations. The most common sites in the dog for mast cell tumors are the skin of the trunk and perineal region (50%) and the skin of the extremities (40%). The remaining 10% arise from cutaneous sites of the head and neck. Mast cell tumors are reported to arise in multiple cutaneous locations in approximately 11% of the cases. The majority of mast cell tumors are found in the head and neck region in the cat. Occasionally, the mast cell tumors are located strictly in the spleen of cats. Occasionally mechanical manipulation during examination of this tumor will result in degranulation of mast cell which results in erythema and wheal formations. DIAGNOSIS OF MAST CELLS TUMORS Diagnosis of mast cell tumors often can be made by a fine needle aspiration cytology but excisional biopsy is required if accurate histologic grading of the tumor is desired. Mast cell tumors are classified as round cell tumors along with lymphosarcoma, histiocytomas and transmissible venereal tumors. Diagnostic work ups of mast cells usually includes a number of procedures. These include a complete blood cell count (CBC), serum chemistry profile, and urinalysis. 1n addition, tine needle aspiration of the lesion, regional lymph nodes and examination of huffy coats or bone marrow helps to determine the extent of tumor involvement. A CBC is valuable in assessing animals with mast cell tumors because those animal patients with systemic mastocytosis occasionally have peripheral eosinophilia and basophilic in addition to circulating mast cells. Mastocytemia is a more common clinical phenomenon in the cat than in the dog. The CBC may also give evidence of gastrointestinal bleeding or gastrointestinal perforation. In general, mastocytosis associated with primary cutaneous tumors is more easily detected by examination of the huffy coat or bone marrow than by examination of peripheral blood. Care must be exercised in interpreting buoy coats since mastocytemia has been reported in a variety of acute inflammatory diseases of the dog including parvo virus infections. Peripheral mast cell counts may be high in cats with mastocytosis and have accounted for up to 25% of the total white cell count. Buffy Coat Smears and Bone Marrow Aspirate Buffy coat smears of blood samples may be examined microscopically for the presence of mast cells but bone marrow smears appear to be more sensitive and are not associated with as many false positives. Bone marrow evaluations should be performed in animals with mast cell tumors. Recent studies have demonstrated that normal clogs have less than 1 mast cell per 1,000 cells in the bone marrow. Veterinary investigators suggest mast cells in greater concentrations than 10/1,000 cells is abnormal. Lymph Node Aspiration Any animal patient with mast cell tumors should be carefully examined for lymphadenopathy in areas draining the primary tumor. Enlarged lymph nodes should be examined for the presence of mast cells as evidence of tumor spread. Such findings have important implications with regard to therapeutic strategies. Radiology Abdominal radiographs may be useful in evaluating dogs and cats. This is especially true in cats because of the high incidence of splenic involvement in this species with mast cell tumors. Chest radiographs rarely identify the presence of pulmonary metastases. In cases of mast cell tumors that involve the hind limbs, perineal or preputial area, abdominal radiographs may be helpful in detecting metastatic lymphadenopathy in the iliac and sublumbar lymph nodes. Miscellaneous Tests Occult blood tests may be useful in evaluating patients with mast cell disease. The stools of dogs with mast cell tumors should be examined for the presence of gastrointestinal bleeding as evidence of GI ulceration. In many cases, feces may contain small amounts of blood that are insufficient to produce melena. Gastrointestinal bleeding can be identified by chemical tests based on blood peroxidase activity that involves catalyzing the conversion of hydrogen peroxide to water and oxygen. The most sensitive test contained orthotoluidine or benzidine as a chemical oxidizer to a color product. These tests are so sensitive that false positives may result if the diet has contained red meat for up to three days before testing. Therefore, careful examination of GI bleeding should be made in mast cell cases and indeed, many patients are routinely treated to block the effects of mast cell hyperhistaminemia or that results in increased gastric acid secretion in GI ulceration. THERAPY Surgical considerations include wide surgical margins with at least 3 cm of normal looking skin around the tumor should be removed when possible. The 3 crn recommendation is a guideline and might not be feasible when the tumor is located on the face, lower limbs or in the inguinal region. It should be remembered that most mast cells extend laterally to adjacent tissue rather than deep into underlying muscles. All excised tumor should be examined histologically for the completeness of excision. Extension of the tumor beyond the surgical borders should prompt either wider excision or radiation therapy of the tumor bed. Approximately 50% of the mast cell tumors recur at the surgical site traditionally. Histologic grade is an important factor in predicting recurrence at the surgical site. Those that are undifferentiated tend to have a higher recurrence rate. Cats with mast cell tumors with splenic involvement often will benefit from splenectomy. Survival times of 10 weeks to 30 months have been reported following splenectomy, even in patients with evidence of systemic mastocytosis. Glucocorticoid therapy frequently results in partial or occasionally complete remissions in canine mast cell tumors. However, cats appear to be less responsive to glucocorticoid treatment. The effect of glucocorticoids is to reduce markedly the number of mast cells in the mast cell tumor. The exact mechanism by which glucocorticoids exert their cytotoxic effects on mast cell tumors is unknown although it may be similar to the effects of glucocorticoids on lymphocytes. The susceptibility of mast cell tumors might depend on the presence of intracytoplasmic glucocorticoid receptor sites. Glucocorticoid receptor sites have recently been found in the cytoplasm of canine mast cell tumors. Although sex steroid receptors for progesterone and estrogen have been recently described in dogs with canine mast cell tumors, the role of sex steroids in the treatment of canine mast cell tumors has yet to be investigated. The type of glucocorticoids administered appears to be unimportant but it has been suggested that intralesional corticosteroid may be more effective than systemic therapy for local disease. Fewer Cushnoid side effects have been seen with short acting glucocorticoids such as prednisone or prednisolone when used in the dog. The usual dose of prednisone is .5 mg/kg orally administered once daily and that of triamcinalone is 1 mg for every crn diameter of tumor intralesionally, administered every two weeks. Remission times are usually 10 to 20 weeks. Dogs that are tumor free after six months however have a low incidence of recurrence and therefore therapy is usually discontinued at this time. Tumor resistance may be caused by the emergence of mast cells with fewer or ineffective glucocorticoid receptors. Survival data based on histologic grade correlates with various chemotherapeutic regimens has not been reported. Ancillary drug therapy is important with canine mast cells. Animals with mastocytosis or palpable mast cell disease should receive H2 antagonists. Cimetidine (Tagamet) reduced gastric acid reduction by competitive inhibition of the action of histamine on H2 receptors of the gastric parietal cells. Ranitidine (Zantac, Glaseo? Inc, Fort Lauderdale, FL), a newer H2 antagonist that requires less frequent administration, is in some clinics. The objective of the therapy is to prevent gastrointestinal ulceration associated with elevated levels of histamine and to treat ulcers already present. Some new evidence indicates that cimetidine may also alter the immune response to this tumor as well as activation of certain alkylating agents. Dogs and cats with evidence of gastrointestinal ulceration and bleeding might also benefit from sucralfate Karafate, Marion Labs Ire, Kansas City, MO) therapy. Sucralfate reacts with stomach acid to form a highly condensed viscous adherent paste like substance that binds to the surface of both gastric and duodenal ulcer sites. The barrier formed at the ulcer site protects the ulcer from potential ulcerogenic properties of pepsin, acid and bile allowing the ulcer to heal. Because sucralfate interferes with absorption of cimetidine, these two drugs should be given at least two hours apart. The usual dosage of sucralfate is 1 gm given orally. Histamine antagonists such as benadryl should be used along with cimetidine prior to and following surgical removal of canine mast cell tumors to help prevent the negative effects of local histamine release on fibroplasia wound healing. HI antagonists also should be used with cryosurgery or hyperthermia therapy. Lomustin (CCNU) is a chemotherapeutic also use in the treatment of mast cell neoplasia. Side effects are bone marrow suppression, hypersensativity in certain dogs, and liver disease. It is recommended to continue with prednisone and cimetidine. Misoprostil has also been used in treatment of this disease. Another recommended ancillary medication is an antiserotonin agent (cyproheptidine). The use of this drug is controversial since serotonin has only been identified in rat and mouse mast cells and definitive studies in the dog and cat are lacking. The use of drugs that stabilize mast cells (sodium chromoglycate) have been described in the treatment of human patients with mastocytosis but not in animals. Radiotherapy has been used alone or in combination with other treatment modalities. Most reports indicate remission rates of 48 to 77%. Doses of 3,000 to 4,000 rads were used in these studies. Total radiation therapy is usually fractionated and delivered over a period of three to four weeks. The use of radiotherapy is somewhat expensive and is confined to referral centers. Mast cell tumors in regional lymph nodes and bone marrow appear to be more resistant to the effects of radiotherapy than those confined to the skin. Response of mast cell tumors to radiation therapy may correlate to histologic grade but has not been studied. PROGNOSIS The natural behavior of mast cells suggests prognosis of this tumor depends on the species, breed, histologic grade, humor location, clinical stage and growth rate. In general, cutaneous mast cell tumors carry a more guarded prognosis in the dog than in cat. Mast cell tumors in the boxer arc usually of a lower histologic grade than when found in other breeds. Mast cell tumors in Siamese are of the less malignant histiocytic type. Histologic grade has been shown to correlate with survival following surgical excision by at least two investigators. The higher the histologic grade (more undifferentiated tumor), the poorer the prognosis. This criteria has not had universal acceptance however, probably due to the precise nature of histologic grading as well as tumor heterogeneity. Clinical staging and the extensiveness of microscopic tumor masses beyond what might be detected clinically also plays an important role in the failure of universal acceptance of the histologic grading system. In the cat, in addition to the histologic grading system described for the dog, the histiocytic mast cell variant tends to carry a better prognosis than the traditional mast cell. Tumor location is considered by many investigators to be an important prognostic feature. Tumors located in the perineal or, preputial area are likely to metastasize both locally and to deep lymph nodes. Clinical stage is a clinical means of assessing tumor spread of the disease process. The higher the clinical stage, the more guarded the prognosis. A high histologic grade, however, should increase the clinical stage at least one level. Growth rate but not tumor size is determined also to be an important prognostic indicator. Dogs that have tumors that grow greater than 1 cm per week have only a 25% chance of living an additional 30 weeks. Reference 1. Ogilvie GK, Moore AS. Mast Cell tumors. In: Managing the
Veterinary Cancer Patient: A Practice Manual. Trenton: Veterinary
Learning Systems. 1995:503-514.
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| What is Feline Immunodeficiency Virus? | Virologists classify feline immunodeficiency virus (FIV) as a lentivirus (or "slow virus"). FIV is in the same retrovirus family as feline leukemia virus (FeLV), but the viruses differ in many ways including their shape. FIV is elongated, while FeLV is more circular. The two viruses are also quite different genetically, and the proteins that compose them are dissimilar in size and composition. The specific ways in which they cause disease differ, as well. |
| How common is the infection? | FIV-infected cats are found worldwide, but the prevalence of infection varies greatly. In the United States, approximately 1.5 to 3 percent of healthy cats are infected with FIV. Rates rise significantly-15 percent or more-in cats that are sick or at high risk of infection. Because biting is the most efficient means of viral transmission, free-roaming, aggressive male cats are the most frequently infected, while cats housed exclusively indoors are much less likely to be infected. |
| How is FIV spread? | The primary mode of transmission is through bite wounds. Casual, non-aggressive contact does not appear to be an efficient route of spreading FIV; as a result, cats in households with stable social structures where housemates do not fight are at little risk for acquiring FIV infections. On rare occasions infection is transmitted from an infected mother cat to her kittens, usually during passage through the birth canal or when the newborn kittens ingest infected milk. Sexual contact is not a major means of spreading FIV. |
| What does FIV do to a cat? | Infected cats may appear normal for years. However, infection eventually leads to a state of immune deficiency that hinders the cat's ability to protect itself against other infections. The same bacteria, viruses, protozoa, and fungi that may be found in the everyday environment--where they usually do not affect healthy animals--can cause severe illness in those with weakened immune systems. These secondary infections are responsible for many of the diseases associated with FIV. |
| What are the signs of disease caused by FIV? | Early in the course of infection, the virus is carried to nearby
lymph nodes, where it reproduces in white blood cells known as
T-lymphocytes. The virus then spreads to other lymph nodes throughout
the body, resulting in a generalized but usually temporary enlargement
of the lymph nodes, often accompanied by fever. This stage of infection
may pass unnoticed unless the lymph nodes are greatly enlarged.
An infected cat's health may deteriorate progressively or be characterized by recurrent illness interspersed with periods of relative health. Sometimes not appearing for years after infection, signs of immunodeficiency can appear anywhere throughout the body.
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| How is infection diagnosed? | Antibody tests detect the presence of antibody in the
blood of infected cats.
Positive results
Negative results
Polymerase chain reaction (PCR) tests are designed to detect short segments of a virus's genetic material. While antibody-based tests are ideal screening tests for infection, in certain situations (such as confirming infection in antibody-positive kittens or determining infection of cats vaccinated with antibody-producing FIV vaccines), PCR-based tests, in theory, would be superior. Although PCR testing methods offer promise and are being actively explored, at this time unacceptable numbers of false-positive and false-negative results prevent them from routinely being recommended. |
| How can I keep my cat from becoming infected? | The only sure way to protect cats is to prevent their
exposure to the virus. Cat bites are the major way infection is
transmitted, so keeping cats indoors-and away from potentially infected
cats that might bite them-markedly reduces their likelihood of
contracting FIV infection. For the safety of the resident cats, only
infection-free cats should be adopted into a household with uninfected
cats.
Vaccines to help protect against FIV infection are now available. However, not all vaccinated cats will be protected by the vaccine, so preventing exposure will remain important, even for vaccinated pets. In addition, vaccination may have an impact on future FIV test results. It is important that you discuss the advantages and disadvantages of vaccination with your veterinarian to help you decide whether FIV vaccines should be administered to your cat. |
| I just discovered that one of my cats has FIV, yet I have other cats as well. What do I do now? | Unfortunately, many FIV-infected cats are not diagnosed until after they have lived for years with other cats. In such cases, all the other cats in the household should be tested, as well. Ideally, all infected cats should be separated from the noninfected ones to eliminate the potential for FIV transmission. If this is not possible-and if fighting or rough play is not taking place-the risk to the non-infected cats appears to be low. |
| How should FIV-infected cats be managed? |
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| How long can I expect my FIV-infected cat to live? | It is impossible to accurately predict the life expectancy of a cat infected with FIV. With appropriate care and under ideal conditions, many infected cats will remain in apparent good health for many months or years. If your cat has already had one or more severe illnesses as a result of FIV infection, or if persistent fever and weight loss are present, a much shorter survival time can be expected. |
| My FIV-infected cat died recently after a long illness. How should I clean my home before bringing in a new cat? | Feline immunodeficiency virus will not survive outside the cat for more than a few hours in most environments. However, FIV-infected cats are frequently infected with other infectious agents that may pose some threat to a newcomer. Thoroughly clean and disinfect or replace food and water dishes, bedding, litter pans, and toys. A dilute solution of household bleach (four ounces of bleach in 1 gallon of water) makes an excellent disinfectant. Vacuum carpets and mop floors with an appropriate cleanser. Any new cats or kittens should be properly vaccinated against other infectious agents before entering the household. |
| Can I become infected with FIV? | Although FIV is a lentivirus similar to HIV (the human
immunodeficiency virus) and causes a disease in cats similar to AIDS
(acquired immune deficiency syndrome) in humans, it is a highly
species-specific virus that infects only felines.
A number of studies have failed to show any evidence that FIV can infect or cause disease in people. |
| Why should I have my cat tested? | Early detection will help you maintain the health of
your own cat and also allow you to prevent spreading infection to other
cats.
Under what circumstances should FIV testing be performed?
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