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 bloodstream. 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.
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 from the 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.
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. Providing free access to water at all times is the most important therapeutic measure for all pets suffering from diabetes insipidus. Doing so will help prevent dehydration and its undesirable effects from setting in as a result of the excess water loss through the kidneys. The prognosis for most pets with diabetes insipidus is good to excellent, assuming that medical therapy and free access to water are provided. Because these pets are prone to dehydration, any signs of illness such as loss of appetite, vomiting, or diarrhea warrant prompt veterinary attention.