Dogs - Endocrine Conditions
Hyperadrenocorticism / Cushing's syndrome
What is it?
This occurs when the adrenal glands overproduce glucocorticoids, or in a situation where animals have been placed on glucocorticoids for medical reasons for a long period of time. Mostly occurs in middle aged to older dogs.
Why does it occur?
Most cases are due to overstimulation of the adrenal gland to produce glucocorticoids by the pituitary gland in the brain, the other 10-15% of cases are due to tumours of the adrenal gland overproducing glucocorticoids.
How can I recognise this condition?
The onset is of this problem is slow and occurs over a period of months. The initial signs can include the following:
Excessive thirst and urination, often leading to house wetting.
Increased appetite.
Muscle weakness and reluctance to exercise, wasting of muscles may be obvious and may result in a stiff gait and inability to run or climb stairs. The abdomen tends to be enlarged and a 'pot-bellied' appearance is common.
Hair loss over the flanks, with the remaining coat being brittle and sparse. The skin may be thin and bruise easily.
Shortness of breath and excessive panting
Some may present with signs related to diabetes mellitus or neurological signs. Urinary infections are also common.
How can this problem be diagnosed?
This condition causes changes in the cell types in the blood which can be picked up by haematological tests, as well as increased cholesterol and liver enzymes. X-rays can show an enlarged liver and changes in bone density. To conclusively diagnose this problem a test is carried out to assess adrenal gland function. Several tests are available, the two most commonly used are probably the low dose dexamethasone suppression test and the ACTH stimulation test. Other tests may be helpful in deciding whether the condition is caused by abnormalities in the pituitary gland in the brain, or in the adrenal gland itself.
What treatment is available?
Most of these cases are treated medically with a drug such as Mitotane or Lysodren, the active component of this causes a degeneration of the tissue producing the excess glucocorticoids. The drug is given with food until the signs of the disease start to disappear. if the animal should appear lethargic or start suffering from vomiting or diarrhoea then your vet may wish to suspend treatment for a period of time. Most dogs respond to treatment within 2 weeks. For long term treatment once weekly treatment is often sufficient but ACTH stimulation tests should be carried out regularly to monitor progress. Some animals may need to be supplemented with glucocorticoids (using a drug called prednisolone) during treatment. Relapses can occur despite treatment.
A new drug treatment 'Vetoryl' has just been released for Cushingoid dogs.
Other treatment options include surgical correction of the problem by removing the tissue producing the glucocorticoids, this is useful if the disease is being caused by a malignant tumour of the adrenal gland.
Some cases can be complicated by having other concurrent problems such as diabetes mellitus making medical management difficult.
Hypoadrenocorticism / Addison's disease
What is it?
This occurs when the adrenal glands fail to function leaving the animal short of two groups of metabolites, glucocorticoids and mineralocorticoids. It is most common in young to middle aged female dogs, with Bearded Collies particularly susceptible.
Why does it occur?
It occurs as a result of the destruction or degeneration of the adrenal tissue, it is thought to be due to an immune system related problem, some cases may be caused by low levels of the compound ACTH which stimulates adrenal function.
What are the presenting signs of this condition?
Dullness, lethargy, weight loss, vomiting, weakness, and dehydration are all common but can also be caused by a variety of diseases. Animals can present with this condition having been suffering from chronic problems typically with a waxing and waning pattern of illness that improves with rest or basic symptomatic treatment, or in an acute addisonian crisis.
An addisonian crisis develops when the condition has progressed to the extent that the patient presents in severe shock and is collapsed. Treatment with intravenous fluids and the drugs mentioned below needs to be undertaken immediately.
Your veterinary surgeon may also notice a slow heart rate. Various tests can be used to give an indication of hypoadrenocorticism, altered blood levels of sodium and potassium, increased blood urea, creatinine, and calcium levels, altered levels of blood cell types, and some specific changes on an electrocardiogram or chest X-ray may all suggest hypoadrenocorticism. Definitive diagnosis requires an ACTH stimulation test
How can this condition be treated?
Treatment involves administering drugs to replace the glucocorticoids and mineralocorticoids the body usually produces of its own accord. This is done using two drugs, prednisolone and fludrocortisone acetate (Florinef). Blood testing may be carried out to monitor the sodium and potassium levels in order to give an indication of the success of treatment.
Pituitary Dwarfism
Most common in the German Shepherd dog. A lack of growth hormone from the pituitary gland in the brain results in retarded development. The condition is inherited through a recessive gene causing cysts to develop within the pituitary gland.
Affected cases do not show abnormality until around the age of 8 weeks, the coat remains soft and woolly, often with balding areas and thin scaly skin. There is a lack of stature and absence of adult tooth eruption.
The diagnosis can be confirmed by use of a growth hormone stimulation test or by measurement of insulin-like growth factor, but often the clinical signs are sufficient to allow a presumptive diagnosis to be made. Often these cases can suffer from other endocrine problems such as hypothyroidism, or hypoadrenocorticism.
Treatment is not often feasible, growth hormone supplementation is expensive and often results in diabetes mellitus developing, there is also a risk of hypersensitivity reactions.
Diabetes Insipidus
What is it?
This is a relatively uncommon condition in dogs which is caused by either the failure to produce a hormone (called antidiruetic hormone or ADH) which controls fluid loss in the kidney, or a failure by the kidney to respond to this hormone. The end result is that the animal is less able to control fluid loss and increases its water intake to compensate.
What are the signs of it developing?
Animals affected by this disorder have an excessive thirst and produce large volumes of urine. The normal amount of water that a animal should require to drink in one day is shown in the table below, the actual amount they choose to drink will vary depending on the water content of the diet.
Weight in Kg |
Normal Water Intake |
Maximum Normal Intake |
5 |
300 ml |
500 ml |
10 |
500-600 ml |
800 ml |
20 |
1-1.2 Litres |
1.6-1.8 Litres |
30 |
1.5-1.8 Litres |
2.4-3 Litres |
40 |
2-2.5 Litres |
3.2-3.5 Litres |
How can the diagnosis of this problem be confirmed?
Your vet will wish to rule out other causes of increased thirst by blood and urine testing and will carry out a water deprivation test to assess whether the animal has the ability to concentrate its urine, affected animals continue to produce weak urine even when they are becoming dehydrated. Following this a test known as an ADH response test can be carried out to confirm the diagnosis.
Can this condition be treated?
The form of the disease which results from kidney insensitivity to the hormone is not treatable, the form created by hormone deficiency is treatable using a drug called desmopressin acetate which is administered once or twice daily for the remainder of the the patients life.
Diabetes Mellitus
What is it?
This is a disease that results in a low blood glucose level. It can be be caused by several problems, but is basically due to an insufficient level of insulin, either because the body cells stop responding to insulin and require a higher amount to extract the same response or because insufficient insulin is being produced.
It is important not to confuse this condition with another called diabetes insipidus which is relatively rare in dogs and causes an excessive thirst but has no effects on glucose metabolism.
Why does it occur?
Insulin is produced by the pancreatic tissue and released into the blood as required, the insulin in the blood binds to the cells allowing them to absorb glucose. Diabetes can be caused by a failure to produce insulin in the pancreas perhaps as a result of diseases such as pancreatitis, immune problems, deficiencies of the islet cells that manufacture insulin, pancreatic cancer, or due to problems causing insensitivity to the insulin in the body tissues such as obesity or hormonal antagonism (high levels of some other substances act against insulin). In cases of hormonal antagonism if the substance which is causing the insulin insensitivity can be identified and removed then it may be possible to cure those cases, for example bitches at a certain stage of the reproductive cycle produce an excess of progesterone which acts against insulin, neutering these bitches at an early stage of the problem can be curative.
Which animals are most likely to suffer from this problem?
Middle and older aged animals are more likely to develop diabetes mellitus. Obesity is a major predisposing factor since it can induce insulin insensitivity.
What are the presenting signs of diabetes?
The major indication of diabetes is an increase in thirst and volume and/or frequency of urination, often leading to inappropriate house wetting, increased appetite, weight loss, sweet smelling breath and inability to exercise for a long period of time.
Diabetic animals can develop cataracts leading ultimately to blindness.
How can the diagnosis be confirmed?
All untreated diabetic patients have a high blood glucose level and usually glucose in the urine. Urine glucose can however also be associated with kidney problems and blood glucose can also be raised by stress and some drugs.
Your vet may wish to carry out other blood tests to investigate whether there is any other concurrent disease that may interfere with the treatment of the diabetes.
How can diabetic patients be treated?
Almost all canine diabetics require insulin which has to be given by once or twice daily injections. The insulin available for use in dogs is either short, intermediate or long acting. The preparation and regime most suitable for an individual animal is best decided by the vet and owner on an individual case basis. The amount and frequency of insulin administered is determined by regularly testing either blood or urine glucose levels.
Diet modifications are essential in successful management of diabetic patients. Meals should be of a constant size and constituency and feedings times should not vary from day to day. Most standard pets food are acceptable and should be fed at around 1 to 1 and 1/2 times the normal requirement. Diets with high fibre and carbohydrate levels are best. In obese animals weight loss is an essential part of disease management. It is also advisable to neuter bitches to prevent hormonal interference with therapy.
What are the likely complications of diabetes mellitus for my pet?
Complications of diabetes therapy can involve the development of hypoglycaemia which is a low level of glucose in the blood and manifests as lethargy, weakness, inability to balance and coordinate movement and may progress to seizures
The most serious complication of diabetes is the development of a ketoacidotic state which necessitates emergency treatment by your vet, this situation is created by a high glucose level and the overproduction of ketones which in turn causes electrolyte upsets in the blood and can result in the patient becoming dehydrated, the signs this is developing are lethargy, inappetance, vomiting, and can progress to the extent of the patient becoming comatose. Your vet will normally treat this situation by administering insulin and intravenous fluids as well as treating any concurrent disease.
The longer term complications of diabetes mellitus include cataract formation which is irreversible, although treatment may be feasible in some cases. Neuropathies (nerve problems) can occasionally develop often interfering with the animals ability to walk properly. Relative uncommon problems with the retina in the eye, and with the kidneys can also occasionally develop.
To try and reduce the likelihood of these problems occurring your vet will wish to regularly check your pet by blood sampling of blood glucose and fructosamine levels.
Cancer of the Thyroid Gland
When and how does it occur?
Cancer of the thyroid gland generally occurs in middle aged to older dogs and appears to be more prevalent in the Boxer, Golden Retriever and Beagle. It can affect one or both lobes of the thyroid gland on opposite sides of the throat. Benign tumours do occur but usually remain small and are not noticed during life, the majority of cases presented with thyroid swellings are therefore malignant tumours. Malignant tumours are known as thyroid carcinomas, benign tumours as thyroid adenomas.
What are the clinical signs of this disease?
Most cases will present with a swelling in the throat region which has been noticed by the owner. Because of its location and the tendency of these masses to spread into the chest the clinical signs seen often involve interference with breathing or swallowing, coughing, hoarseness, sometimes vomiting, weight loss and inappetance. For those animals which do not have a palpable swelling in the neck region the reason for presentation is often that they are starting to become hyperthyroid, showing increased thirst, urination, and weight loss despite an increased appetite. Other symptoms such as weakness and restlessness, muscle wasting, intolerance to heat, and increased heart rate can occur.
How can the diagnosis be confirmed?
Useful information on whether the mass is a functional (i.e. producing thyroid hormones and causing hyperthyroidism) tumour or non functional (cancerous tissue not producing hormones) can be gained from blood sampling. Those cases with non functional tumours can show increases in levels of the liver enzymes ALT and ALKP along with increased levels of calcium, urea and a mild anaemia. Functional tumours may produce a slightly raised PCV and calcium and an increase in the level of the thyroid hormone T4. Fine needle aspiration will allow some cells to be removed and examined and definitive diagnosis can be obtained by biopsying the mass and carrying out histopathological examination.
How can this condition be treated?
Small tumours can usually be easily removed, larger tumours are more likely to have spread, and if this is the case then removing the original tumour is pointless as it will not improve the life expectancy of the animal. It is important before considering surgery to X-ray the chest to see whether or not there is any evidence of spread.
Those cases which have tumour tissue in both lobes of the thyroid gland present a further problem in that surgical removal of the entire gland will not only mean that thyroid hormones will have to be administered for the remainder of the patients life but also that it may be necessary to also removed both attached parathyroid glands during the surgery, which means lifelong administration of dihydrotachysterol and calcium. For this reason these cases have a poorer prognosis.
If the tumour is of a type known as a follicular carcinoma the treatment can be undertaken using radioactive iodine. This involves administering the iodine to the patient which will then be taken up by the thyroid glands and destroy the cancerous cells. This procedure is limited to a few specialist centres and depends on the ability of the cancer tissue to absorb the iodine.
Additional medical therapy involves administering thyroid hormones during and after treatment and sometimes chemotherapy using doxirubicin, often along with cyclophoshamide and vincristine, the side effects can however be severe.
What is the prognosis?
Complete removal of all tumour tissue usually results in another 2-3 years of life, in those cases where this is not feasible then the life expectancy depends on the rate of tumour development but may be as short as a few months.
Hypothyroidism
What is it?
In dogs the thyroid gland lies in the throat region and consists of two separate lobes. The hormones produced by the thyroid have an affect on many body tissues and regulate the metabolic rate of the body. Hypothyroidism is a deficiency of the thyroid hormones, it is a common disorder in dogs occurring most frequently in middle aged to older animals in the medium to large sized breeds.
What causes this problem?
The disease can be of two forms, the primary form which is the insufficient production of thyroid hormones and is responsible for most cases of hypothyroidism in the adult dog, or the secondary form which develops as a result of a lack of stimulation of the gland by TSH secreted from another gland in the body. The end result in both cases is a low level of thyroid hormone in the body.
How would I recognize this condition in my dog?
There are many signs which can result from hypothyroidism, the condition usually develops slowly. Initially you would expect to see hair loss along the flanks and on the tail, while the rest of the coat is dry and lacks shine. Lethargy and dullness with a reluctance to exercise and a tendency to gain weight can develop along with a tendency to seek warm places. Skin can increase in thickness causing a 'depressed' facial expression.
Your veterinary surgeon may also note signs such as a slow heart rate, some muscular or nerve disorders, eye problems and possibly indications of other concurrent hormonal problems such as hypoadrenocorticism or diabetes mellitus.
How can we confirm the diagnosis?
If the clinical signs support a diagnosis of hypothyroidism then blood testing is necessary to confirm the problem, most cases will have a high cholesterol level, increases in liver enzyme levels, and a specific type of anaemia. The definitive tests involve measuring the levels of thyroid hormone in the blood although this can be complicated by other illnesses or drug treatment and in doubtful cases a TSH stimulation test can be required. This involves measuring the thyroid hormone levels in the blood then injecting a dose of TSH (thyroid stimulating hormone), and repeating the blood measurement 6 hours later. The changes in blood hormone levels can usually differentiate between hypothyroid and normal animals.
A newly developed test for TSH (thyroid stimulating hormone) is proving useful, especially if carried out in combination with the normal thyroid hormone measurement.
What can be used to treat this condition?
A drug known as soloxine is available to treat hypothyroidism. this is usually administered twice daily and may take up to 6 weeks to give improvement. Your veterinary surgeon will probably wish to blood sample your dog 6 weeks after start of therapy to monitor the blood levels of the drug.