pets disease

The organs of the immune system include the bone marrow, the thymus, the spleen, and the various lymph nodes and aggregates of lymph tissue spread throughout the body.
Bone marrow
As mentioned before, all cells of the immune system originate within the bone marrow. Many stay put and undergo maturity right where they are; other cells are shuttled off to the thymus.
The spleen
The spleen is an organ most have heard about; its various functions include filtering blood and providing a storehouse for blood cells.

This type of diabetes should not be confused with diabetes mellitus, which involves abnormal glucose metabolism. Diabetes insipidus involves abnormal water metabolism, and it occurs when there is a lack of the antidiuretic hormone (ADH). ADH is normally produced by the hypothalamus of the brain, yet it exerts its effects on the kidneys, causing water to be recaptured from the kidney tubules rather than being lost in the urine. As a result, the delicate water balance within the body is maintained with this hormone’s influence.
Too little ADH may be produced by the hypothalamus as the result of an inherited defect or due to head trauma that damages the hypothalamus. In addition, defects present in the kidneys at birth or acquired later in life can make the kidneys unresponsive or only partially responsive to the effects of ADH. If any of these conditions occur, then diabetes insipidus results.
Pets with diabetes insipidus exhibit increased urinations, incontinence (especially at night), and an increased water consumption. Routine laboratory work usually reveals nothing too significant except for very low urine specific gravity (dilute urine). However, a laboratory workup will help rule out other potential causes of the clinical signs seen, such as diabetes mellitus, Cushing’s disease, and kidney disease. If these are ruled out, then a tentative diagnosis of diabetes insipidus becomes more likely. To obtain a definitive diagnosis, special laboratory tests, such as water deprivation tests, plasma ADH determinations, and ADH trials, are required.
Diabetes insipidus caused by poor ADH production from the hypothalamus can be treated by administering a natural or synthetic ADH supplement. These can be administered by injection or drops applied directly into the eyes. Such treatment will be required on a daily basis to control the clinical signs. Therapy is usually for life. Diabetes insipidus caused by kidneys that are nonresponsive to ADH is more difficult to control. Special drugs can be utilized to slow water loss and reduce thirst in pets so affected.

Diabetes mellitus is one of the more common endocrine diseases affecting both dogs and cats. The condition is caused by a deficiency in (or in some cases, a resistance to) the hormone called insulin, which is created by special cells within the pancreas. Insulin is responsible for regulating the uptake of blood sugar, or glucose, into cells and tissues of the body for use as energy. Any disease involving the pancreas, including chronic pancreatitis, can cause deficiencies in this hormone. In addition, autoimmune disease, in which the pet’s body creates antibodies against its own insulin, has also been known to occur. Overweight pets, especially obese cats, are at high risk for diabetes mellitus. Finally, there is evidence that, in dogs, a risk for diabetes can be inherited. Middle-aged female dogs seem to be more at greater risk.
When a deficiency in insulin does occur, the transfer of glucose fromthe bloodstream to the tissues does not occur; hence, blood glucose levels become elevated. At the same time, the cells, tissues, and organs of the body don’t receive the proper nutrition needed to maintain their function, and they start to look for other sources of energy in the body, namely, proteins and fats. And this is where the problems start.
Dogs and cats with this disease will exhibit an increase in water consumption and, consequently, urination. As the body calls on these alternate sources of energy, pronounced weight loss results. In addition, as body fat stores are called on and metabolized for energy, an excess of ketone bodies, by-products of fatty breakdown, accumulate within the body. In large amounts, these ketone bodies have the ability to damage the liver and to depress the nervous system, leading to depression and coma. Over time, the increased glucose levels within the blood can lead to cataracts and blindness.
Diabetic pets have a decreased resistance to infection; as a result, they often suffer from chronic skin and bladder infections. Damage to small capillaries within the body caused by diabetes mellitus can lead to secondary kidney disease, blindness, and gangrene of the skin and extremities.
The clinical signs associated with diabetes mellitus are similar to those in conditions such as Cushing’s disease, kidney disease, and diabetes insipidus; therefore, a thorough laboratory workup is needed to ensure a correct diagnosis. Blood tests on pets with diabetes mellitus will consistently reveal elevated glucose levels, and evaluation of urine samples will reveal the same. In addition, levels of the blood protein known as fructosamine will be elevated as well, even if blood glucose levels are borderline. Such findings, along with the exclusion of other potential causes of the clinical signs, can lead to a definitive diagnosis of diabetes mellitus.
Diabetes mellitus can be classified as uncomplicated or complicated. Uncomplicated cases might exhibit mild to moderate signs of the disease, yet none are truly life-threatening. In contrast, pets diagnosed with the disease and exhibiting marked depression, vomiting, diarrhea, heavy breathing, and/or severe weight loss should all be considered complicated cases and should always be considered medical emergencies. In most of these cases, the high levels of ketone acids produced as a result of increased fat metabolism lower the pH of the blood sufficiently to cause the harmful effects represented by the clinical signs. These pets usually become severely dehydrated at the same time.
Treatment consists of immediate hospitalization with intravenous infusion of replacement fluids, medications designed to increase the pH of the blood (if indeed the pH is too low), and insulin. The levels of insulin given and corresponding blood glucose must be monitored closely, since too much insulin is even worse than not having enough. If excess insulin is given, the pet could quickly become hypoglycemic and go into convulsions. Good monitoring and careful planning on the part of a veterinarian will help prevent this.
Often, dogs and cats are presented with complicated cases of diabetes mellitus because of some underlying disorder adding to the problem. For instance, many of these pets suffer from coexisting disorders such as obesity, pancreatitis, kidney disease, and heart disease. In order to increase the chances of recovery from a complicated case of diabetes mellitus, these disorders must be addressed at the same time. When a pet finally comes home, it will be the owner’s job to ensure that the proper insulin dosage (as prescribed by the veterinarian) is given each day and that proper adjustments are made (per veterinary instruction) as needed.
Keep in mind that it is better to give a diabetic pet too little insulin than to give too much. Adjustments to insulin dosages need to be made slowly and carefully in these uncomplicated cases. Giving too much insulin can cause insulin shock (hypoglycemia), which can be fatal. Signs of this can include trembling, weakness, incoordination, and if it is not rapidly corrected—seizures. Owners of diabetic pets should always keep a bottle of pancake syrup or honey around in case of insulin shock. Two tablespoons or more given orally should be used if such a reaction is suspected.
Owners must keep accurate records each day as to their pet’s urine glucose readings, insulin dosage, overall attitude and/or clinical signs that day, and appetite. These will not only be useful in regulating insulin levels, but such records can provide a veterinarian with valuable information should a question or problem ever arise. Periodic blood tests by a veterinarian will also be needed to determine the efficacy of treatment.
A large number of uncomplicated cases of diabetes mellitus in cats are non-insulin-dependent and do not require specific insulin therapy. In these instances, feeding high-protein, low-carbohydrate diets and administering oral medications designed to either stimulate insulin release from the pancreas, decrease insulin resistance, and/or slow glucose absorption from the intestines are indicated. However, if ketosis occurs at any time during treatment, insulin therapy will be needed.
Strict feeding schedules for pets with diabetes mellitus must be followed. Rations high in fiber and protein with restricted fat and special carbohydrate sources are ideal for maintaining the diabetic pet.
Diabetic dogs should be kept on a consistent exercise program, since fluctuations in the amount of exercise performed from one day to the next can affect blood glucose levels and make proper insulin dosing difficult. If a dog or cat is obese to start with, it will need to be placed on a weight reduction program.
Finally, intact females that are diabetic should be spayed. By eliminating female hormonal influences on glucose levels in the body, achieving and maintaining proper insulin levels will be greatly enhanced.

The parathyroid glands, which are closely associated with the thyroid glands in dogs and cats, produce a hormone that is responsible for increasing calcium levels in the blood by drawing stores of this mineral from bone and other regions of the body. Hyperparathyroidism is a condition initiated by a deficiency of calcium within the blood stream. This can result from diet regimens that are high in phosphorus (nutritional hyperparathyroidism), such as all-meat diets, or, more commonly in older pets, from increased phosphorus levels in the body caused by kidney disease. When such a calcium deficiency occurs, the parathyroid glands respond by secreting large amounts of hormone, which draws calcium out of bone in an attempt to normalize blood calcium levels. Over time, these bones become weakened and prone to stress injury.

While Cushing’s disease is caused by too many corticosteroids circulating within the body, Addison’s disease is caused by the exact opposite: inadequate amounts of circulating corticosteroids. This includes not only the glucocorticosteroids produced by the adrenal glands but the mineralocorticoids as well. Because the latter are so vital at maintaining a fluid and electrolyte balance within the body, Addison’s disease can be acutely life-threatening in the affected individual. Like Cushing’s disease, Addison’s disease is primarily a disease of dogs; it is rare in cats.
Causes of this disease in dogs can include tumors, infections, autoimmune diseases, and toxins. It can also occur secondarily to overtreatment with corticosteroids.
The clinical signs seen resemble those exhibited by pets afflicted with viral or parasitic gastroenteritis—namely vomiting, diarrhea, and dehydration. Loss of appetite and weight loss accompany these signs as well, yet there might be an increase in water consumption. Because the levels of sodium and potassium, two electrolytes vital to proper muscle contraction, are disrupted, profound muscle weakness, including a slowing of the rate at which the heart muscle contracts, are also observed. In severe cases, collapse of the entire circulatory system, with shock and then death, has been documented.
Diagnosis of Addison’s disease can made based on the history (i.e., long-term corticosteroid therapy), clinical signs seen, and determining the ratio of sodium to potassium in the bloodstream. Marked increases in potassium and decreases in sodium are indicative of primary Addison’s disease. Physical examination and electrocardiograms will reveal abnormal heart activity in these patients as well.
If Addison’s disease is diagnosed or suspected, treatment should be instituted immediately. Dehydration is combated with intravenous fluids, and injections of mineralocorticoids are administered to stabilize fluid and electrolyte levels.
For cases of primary Addison’s disease, periodic injections with mineralocorticoids will be required throughout the dog’s life to prevent relapses from occurring. If the condition was caused by the sudden cessation of glucocorticosteroid therapy, such therapy is reinstituted and then gradually tapered off over weeks to months.

Steroid hormones, specifically the class known as glucocorticosteroids produced by the adrenal glands, serve over 50 vital functions within the body. Some of the more important ones have to deal with carbohydrate, protein, and fat utilization and with maintaining water and electrolyte balance within the body. Veterinarians fighting allergic reactions or inflammation in dogs and cats rely on glucocorticosteroids for their anti-inflammatory effects when given at low dosages. Similarly, since high doses of glucocorticosteroids can suppress the immune system, they are quite useful in treatment against autoimmune diseases in pets, including pemphigus, a disease that causes severe skin lesions in affected dogs.
Unfortunately, since steroid hormones help maintain a delicate balance within the body, an overproduction of these hormones within the body can upset this balance. This is precisely what happens in Cushing’s disease. An overproduction of glucocorticosteroids from the adrenal glands occurs within the body, usually as the result of a tumor affecting one or both glands, or, more commonly, a tumor affecting the pituitary gland. The disease is most common in dogs over 8 years of age. Furthermore, poodles, boxers, and dachshunds seem to be afflicted with a greater frequency than other breeds. Fortunately, the condition is rarely seen in cats.
Some of the clinical signs seen in dogs with Cushing’s disease include a marked increase in water and food consumption, an increase in elimination activity, lethargy and exercise intolerance, and a generalized reduction in muscle size and tone, which, when it affects the muscles of the abdominal wall, leads to a characteristic pot-bellied appearance.
The skin and coat changes that occur in a dog with Cushing’s disease might be the first clues as to the existence of the problem. A generalized thinning of the haircoat and skin will be seen, with flakiness, pigmentation, and secondary infections. Eye problems are common in these dogs, too, with recurring ulcers affecting the cornea. Because high levels of steroids have a suppressing influence on the immune system, secondary infections, especially bladder infections, are often seen in these dogs as well. Finally, if a tumor is present in the pituitary gland at the base of the brain, neurological problems might occur as pressure is increased on the brain.
These signs can lead a clinician to suspect Cushing’s disease, but more extensive blood testing and radiographic X rays are usually required to confirm a diagnosis. Measuring actual blood levels of steroids within the bloodstream is one way to test for Cushing’s disease; other methods include injecting small amounts of special synthetic hormones, designed to alter the production of steroids within the body, into the dog and measuring the body’s response to them. If these hormones cannot alter the steroid production, then a diagnosis can be made.
Once a dog is diagnosed with Cushing’s disease, therapy may be instituted in a number of ways. Surgical removal of the tumor in either the adrenal glands and/or pituitary gland can be attempted, but this is a very difficult procedure associated with many postoperative complications.
Chemotherapy can be employed to target the adrenal glands and reduce the amount of steroids being produced by them. Used correctly, this treatment can reduce or eliminate the clinical signs seen and greatly improve a dog’s quality of life. Close veterinary monitoring for the appearance of side effects during the initial treatment stage is recommended. Therapy is usually required for life.
Because of the intense management required with these modes of therapy, some pet owners prefer to stick to conservative treatment when dealing with this disease in their dogs. In these cases, dogs should be placed on high-protein diets to counteract protein loss caused by the disease. In addition, treating secondary problems as they arise—such as skin infections, bladder infections, and corneal ulceration is necessary. Because the tumors responsible for Cushing’s disease are usually slow-growing, most dogs can live for up to 2 years with this treatment approach alone.

A condition of hyperthyroidism in cats is caused by an increase in circulat ing levels of thyroid hormones, namely, thyroxine (T3) and triiodothyronine (T4). When it occurs, hyperthyroidism is most commonly seen in cats greater than 8 years of age, usually as a result of a tumor involving the thyroid gland. Because thyroid hormone helps regulate the body’s metabolism, the clinical signs seen with hyperthyroidism can be directly related to the exaggerated increase in the cat’s metabolic rate. These symptoms may be mild to severe depending on the amount of excess hormone being secreted. Signs typically include noticeable weight loss in the presence of a voracious appetite, nervousness and hyperactive behavior, and a rough, unkempt haircoat. Other less common signs seen include increased water consumption, regurgitation (due to rapid overeating), panting, and breathing difficulties, especially if the thyroid glands are grossly enlarged. In addition, many cats with elevated thyroid levels also suffer from inflammatory bowel disease (IBD). As a result, vomiting and/or diarrhea related to this may be seen in the hyperthyroid feline as well.
Diagnosis of hyperthyroidism is made through the evaluation of clinical signs, physical exam findings, and special laboratory tests. On physical examination, nodules can usually be palpated in the neck region because of glandular enlargement. In addition, a rapid heart rate and pulse are often detected because of the effects of the thyroid hormones on the heart. This cardiac affect can be especially dangerous in cats suffering from concurrent cardiomyopathy. A diagnosis of hyperthyroidism can also be verified through the use of special tests designed to detect levels of thyroid hormone in the blood.
If this condition is definitively diagnosed, a number of treatment options exist. The type of treatment chosen will depend on the severity of the thyroid hormone elevation and other underlying disease factors (such as the presence of heart disease or kidney disease). Medical treatment for hyperthyroidism involves the administration of special drugs designed to inhibit production of thyroid hormone by the thyroid gland, thereby controlling clinical signs. Side effects from giving such drugs can include anemia, immune cell suppression, decreased appetite, vomiting, weakness, and itching. Since most cats must stay on this medication for the remainder of their lives, close monitoring by and periodic communication with a veterinarian is essential.
Yet another form of medical therapy that yields successive results in hyperthyroid felines is called radioactive iodine therapy. This type of therapy selectively destroys malfunctioning thyroid cells using radiation.
Most cats suffering from hyperthyroidism will respond favorably to medical therapy. However, if drug therapy fails to resolve the disorder and radioactive iodine therapy is unavailable, surgical removal of the thyroid gland (partial or complete thyroidectomy) must be performed. If extensive tumor involvement necessitates the removal of the thyroid, then daily thyroid hormone supplementation will be required for the remainder of the cat’s life. Felines placed on such supplementation should have blood thyroid levels checked every 6 to 8 months to ensure that adequate levels are being given.
An inherent risk associated with the surgical removal of the thyroid gland in cats is a complication known as hypoparathyroidism. This condition, characterized by low blood calcium levels, is caused by the inadvertent removal of the parathyroid gland (tightly adhered to the thyroid gland) when the thyroid tissue is removed. Signs of low blood calcium, which normally arise within 3 days of parathyroid gland removal, include profound weakness, muscle tremors and spasms, and in some cases, seizures. Felines suffering from this postsurgical complication require prompt treatment with calcium supplements. These supplements, as well as vitamin D tablets, will be required for life to help maintain proper calcium levels within the body.

The thyroid gland, through production of thyroid hormones, functions to influence nutrient and oxygen utilization within the body, hence affecting overall metabolism. As a result, deficiencies in thyroid hormone or interference with its function can have profound effects on the body. In dogs, immune system malfunctions, iodine deficiencies, incomplete thyroid gland development, and pituitary gland malfunctions can all lead to a condition of hypothyroidism. Predisposed breeds include cocker spaniels, Dobermans, dachshunds, beagles, and golden retrievers.
Clinical signs associated with this disorder are varied, owing to the tremendous scope of thyroid hormone function. Dogs with hypothyroidism tend to be lethargic, sleeping a lot and tiring easily after exercise. Some exhibit a profound intolerance to cold floors or cool environmental temperatures. Puppies so affected might seem to be slow learners when it comes to training. As the skin around the face of these dogs often thickens as a result of the disease, a dog’s voice might change to a lower pitch, and facial features might appear droopy or sad.
In addition, hypothyroid dogs may also have poor appetites, yet still gain weight. Over 50 percent of dogs afflicted with hypothyroidism will exhibit changes to the skin and haircoat. A loss of the undercoat occurs, resulting in a thinned, poor-looking coat. Skin thickening occurs, and secondary seborrhea is not uncommon. Finally, eye problems, neurologic disorders, reproductive infertility, arthritis, and aggressive behavior could all have their roots in a thyroid disorder. A veterinarian can evaluate your pet’s thyroid function right at the office. A simple blood test can be used to screen thyroid hormone levels within the body (Fig. 18.1). If a problem is found, then more extensive thyroid function tests may be ordered to help determine the extent of the problem. If a dog is taking corticosteroid hormones for other problems at the time of the testing, the results could come back falsely low. As a rule, however, if clinical signs correlate with blood test results, then it is safe to assume that a condition of true hypothyroidism exists.
Regardless of the underlying cause, treatment of hypothyroidism in dogs involves daily supplementation with synthetic thyroid hormone tablets. Thyroid hormone levels will need to be monitored during the initial stages of treatment to ensure that the proper dosage is being met. For the most part, this is a medication that affected dogs will need to stay on for the rest of their lives. Clinical response to medicating is usually seen within 2 weeks after initiation, with resolution of signs occurring soon after.

Within the bodies of all mammals, a complex network of glands (the endocrine system) is responsible for the production and secretion of special proteins and lipids (fats) called hormones. In turn, these hormones serve to regulate many vital functions within the body, from growth and development to digestion and utilization of nutrients. Like the nervous system, the endocrine system assumes a regulatory role within the body, and its proper function is essential to the overall health of the animal. Without the endocrine glands and their hormones, a state of chaos would quickly ensue within the body, as the functional harmony existing between the various organ systems would cease to exist.

Anatomy and Physiology
Hormones can be protein in nature, or they can be fashioned from special fatty components, known as steroids. “Steroid” is one of the most misused and widely misunderstood terms in today’s society. Corticosteroids are a special group of steroids produced by the adrenal glands that are vital to many everyday functions within the body. Synthetic derivatives of this steroid group are commonly used, among other things, to reduce pain and inflammation resulting from musculoskeletal injuries.
Androgens (i.e., testosterone) and estrogens, the sex hormones that influence reproductive activity and secondary sexual characteristics, are also types of steroid hormones produced naturally within the body.
Anabolic steroids, probably the most notorious members of the steroid family, are actually synthetic derivatives of the male androgenic steroid hormones. This is the group that has been largely exploited by athletes for increased muscular strength and size.
Although all the different classes of steroids mentioned above, whether natural or synthetic, share a similar structural design, it is easy to see that their functions and effects differ greatly between each class.
Both protein and steroid-type hormones are secreted directly into the bloodstream from the glands or organs that produce them, and circulate to their specific target cells or organs, where they exert their effect. The amount of hormone required to exert its particular effect is precise. If present in too great a quantity, or if supplies are deficient, abnormal function of its target cells or organs result. As a result, hormonal activities within the body are governed by complex negative feedback mechanisms, which ensure proper blood levels at all times. Unfortunately, certain disease conditions involving the endocrine glands and organs can disrupt this delicate balance, which can pose serious health problems.
The hypothalamus, located at the bottom portion of the brainstem, functions as an integration center between the nervous system and the endocrine system. Nervous system functions of the hypothalamus include regulation of body temperature, emotional behavior and sleep, and control of food and water intake. As an endocrine organ, the hypothalamus secretes the hormone ADH (antidiuretic hormone), which controls the water balance within the body; oxytocin, which stimulates lactation and uterine contractions; and a variety of other hormones that exert control over the pituitary gland.
The pituitary gland produces hormones that have effects on other endocrine glands, such as the thyroid and adrenal glands. In addition, pituitary hormones also influence growth and reproductive patterns. In dogs, Cushing’s disease, a condition characterized by an oversecretion of adrenal gland hormones, is most commonly caused by a tumor of the pituitary gland.
Hormones produced by the thyroid gland control the rate of growthand metabolism within the body, as well as decrease calcium levels within the bloodstream. Closely associated with the thyroid gland are the parathyroid glands, which produce a hormone that counteracts the action of a certain thyroid hormone by increasing blood calcium levels. This balance between the thyroid and parathyroid glands helps maintain proper blood levels of calcium at all time. Too much parathyroid hormone can result in excess resorption of bony tissue, resulting in metabolic bone disease.
The adrenal glands produce a variety of hormones, each exerting unique effects within the body. Among other things, adrenal hormones influence carbohydrate and protein metabolism and storage (cortisol, cortisone), help the kidneys regulate sodium and potassium levels (aldosterone), and control blood pressure and heart rate (epinephrine and norepinephrine). Certain organs can double as endocrine glands. The pancreas is not just responsible for producing digestive enzymes; it secretes two hormones, insulin and glucagon, both involved in carbohydrate (sugar) metabolism within the body. Insulin functions to lower blood sugar by increasing its uptake and utilization by the body organs. Counteracting the effects of insulin, glucagon increases blood sugar levels by decreasing its uptake into the liver and fatty tissue. Diabetes mellitus is a disease in which not enough insulin is produced by the pancreas, prohibiting cells and organs from extracting carbohydrates out of the bloodstream.
Other organs exhibiting endocrine functions include the stomach,which produces hormones that regulate digestion; the ovaries and testicles, which, together with the adrenal gland and placenta (in pregnant females), produce the sex hormones; the kidneys, which secrete hormones that influence blood flow and filtration within the kidneys themselves; and the thymus gland, with hormonal activity that influences the cells of the immune system.