Why We Should Pay Attention to Concurrent Diseases in Diabetic Dogs:
Often, diabetes is not the only disease in a diabetic dog. Diabetes may be associated with other disease(s) that your vet will necessarily have to take into account for establishing the animal’s treatment. These diseases are called diabetes concurrent diseases or comorbidities.
Some diseases are more frequently diagnosed in diabetic dogs than in non-diabetic dogs, although the links between these pathologies are not understood. The veterinarian has to suspect the presence of these diseases in any diabetic dog and make complementary examinations to rule out or ascertain their presence.
The most commonly identified concurrent disorders in diabetic dogs include hyperadrenocorticism (Cushing’s), urinary tract infection, dermatitis, otitis, acute pancreatitis, neoplasia, and hypothyroidism (1)
Canine hyperadrenocorticism (Cushing’s syndrome)
Hyperadrenocorticism results from chronic excessive production of cortisol hormone by the organism. This over secretion may originate from different causes:
– Tumor(s) of the pituitary gland. The pituitary gland is a small gland located at the base of the brain. It is responsible for the secretion of many important hormones. One of them is the adrenocorticotropic hormone (ACTH) that triggers cortisol production and secretion by the adrenal glands. A tumor of the pituitary gland increases its mass and consequently increases ACTH production. Increased levels of ACTH induce increased secretion of cortisol by the adrenal glands. This mechanism accounts for 80-85% of hyperadrenocorticism cases in dogs.
– 15-20% of hyperadrenocorticism come from benign or malignant tumors of the adrenocortical gland(s). The adrenal glands are situated on the anterior part of the kidneys. The adrenal cortex is responsible for the production and release of hormones: cortisol, aldosterone and testosterone. Tumors increase the adrenal mass and therefore the production of cortisol.
– Long term administration of glucocorticoids (common anti-inflammatory medication) may result in iatrogenic Cushing’s disease.
Hyperadrenocorticism affects mainly aging dogs over 9 years old and slightly more females than males.
In diabetic dogs, excess of cortisol induces a resistance to insulin. As a consequence, the vet will have to increase the insulin dose in order to achieve a good glycemic control.
Like diabetic dogs, dogs with hyperadrenocorticism are often polyuric (excessive urination), polydipsic (excessive drinking) and polyphagic (excessive hunger). In most cases, these dogs also present with a characteristic abdominal enlargement in a potbelly form. Weakness of abdominal muscles and increase in abdominal contents (enlarged liver and bladder, redistribution of fat in the belly) result in a pendulous abdomen.
The muscle weakness also concerns the other part of the body: the dog loses its abilities to exercise and may even limp slightly.
Hyperadrenocorticism is also associated with hair loss, pruritus and respiratory disorders (panting).
Suspicion of hyperadrenocorticism is based on symptoms observation. Then, a series of routine examination (complete blood count (CBC), urine and blood analysis) permits to see whether further investigations are needed.
If the preliminary tests are consistent with the presence of hyperadrenocorticism, the veterinarian surgeon will perform a “Low Dose Dexamethasone Screening test” (LDDS). It consists of injecting the dog with a low dose of dexamethasone and of measuring blood cortisol 8 hours after injection. Abnormal high dose of cortisol indicates a high probability of hyperadrenocorticism. This test may be completed by an ACTH stimulation test and/or a urinary cortisol test.
Your vet may want to know more about the reason for the hyperadrenocorticism and try to discriminate between pituitary origin and adrenocortical tumor. In this case, the LDDS test may indicate a pituitary origin if the cortisol concentration decreases 4 hours after dexamethasone injection. If not, she will have to perform a “High Dose Dexamethasone Screening test” (HDDS).
Treating a dog with hyperadrenocorticism is not an emergency issue. The signs develop slowly and the disease may remain unnoticed for a long period of time before it leads to a vet consultation.
The veterinarian surgeon may well not try to investigate the cause of hyperadrenocorticism and propose you to proceed right away to the treatment. Trilostane (Vetoryl®) is registered for hyperadrenocorticism of both origins. Alternatively, she may prescribe (op’DDD), off label. The results of the treatment are often excellent and allow the vet to evaluate the accuracy of her diagnosis.
Surgery requires differentiating between a pituitary tumor and an adrenal hyperplasia. It can be contemplated mainly for Adrenal Tumor Hyperadrenocorticism (ATH) for which it is the ideal treatment. On the other hand, surgery is much more questionable for dogs with Pituitary Dependent Hyperadrenocorticism (PDH): the size (very small) and the location (very close to the brain) of the pituitary gland make surgical intervention only achievable to very experienced veterinarian surgeons.
The thyroid is composed of two large glands located just under the larynx, on both sides of the trachea. It produces and secretes the thyroid hormones: triiodothyronine (T3) and thyroxine (T4).These hormones play a central role in the regulation of the global metabolism in the organism. They increase basal metabolism, heart rhythm, ventilation rate, generate body heat…
More than 95% of hypothyroidism cases in dogs are caused by thyroid glands atrophy. It results in a decreased secretion of the thyroid hormones. This simple mechanism is called primary hypothyroidism.
Weight gain results from a metabolic disorder. Exercise intolerance, lethargy, dullness and a propensity to gain weight without eating more are the most frequent signs of hypothyroidism. The owner may not notice them early because of their progressive apparition.
Skin disorders are less frequent but easier to detect. Hypothyroid dogs lose their ability to regrow their hair. Alopecia progressively develops, especially in skin regions exposed to friction. Other dermatologic signs may develop: impaired wound healing, bruises, increased sensitivity to infections.
Hypothyroidism also causes many neuromuscular disorders. The most frequent are facial nerve paralysis, weakness, muscle wasting.
Once the clinical symptoms have been identified, the initial screening test consists of measuring the blood basal level of the thyroid hormone thyroxine (T4). A successful treatment with levothyroxine sodium confirms the diagnostic accuracy.
Some clinicians prefer getting more information on the disease causes before starting the treatment. They can use numerous types of tests that measure the blood concentration of thyrotropin (TSH = hormone that is secreted by the pituitary gland and that is the major modulator for the secretion of the thyroid hormones), of triiodothyronine (T3) thyroid hormone or of different forms of the T4 hormone.
Synthetic levothyroxine is the mainstay of the treatment of hypothyroidism. It is administered orally once to twice a day. It restores of the thyroid hormones level back to normal. The symptoms should resolve within the 2 months after the beginning of the treatment. The first symptoms that improve are general behavior, alertness and willingness to exercise. Your vet will regularly monitor the thyroid hormones level to check the effectiveness of the treatment and adjust the doses.
Liothyronine sodium may be prescribed when the treatment with levothyroxine does not prove clinically effective even after several dose adjustments.
In case of primary hypothyroidism, i.e. the disease is caused by an atrophy of the thyroid glands, the dog can live a normal life if well treated. If the disease affects a puppy, or if the disease comes from a disorder of the pituitary gland (secondary hyperthyroidism), the prognosis ranges from guarded to severe and the life expectancy of the animal will be shortened.
A neoplasia consists of the abnormal development of tissues into neoplasms [http://medical-dictionary.thefreedictionary.com/neoplasm], such as tumors. These tumors may be benign or malignant (cancer).
Get to the next section: treatment of diabetes in dogs(1) Hess R. S. et al. Concurrent disorders in dogs with diabetes mellitus: 221 cases (1993–1998). Journal of the American Veterinary Medical Association. 2000, Vol. 217, No. 8, 1166-1173 [divider]