Endocrine conditions

By | 2011-11-20

Adult-onset growth-hormone-responsive dermatosis

A poorly-understood syndrome of unknown cause. Basal growth hormone levels are low and unresponsive to stimulation. Other pituitary functions seem normal. The condition is characterised by bilaterally symmetrical areas of alopecia and hyperpigmentation initially in the areas of friction, e.g. the neck.

Central diabetes insipidus (CDI)

A polyuric state caused by a complete or partial lack of antidiuretic hormone (vasopressin) which is normally produced in the neuro-hypophysis of the pituitary. Urine specific gravity is usually hyposthenuric. In the dog, most cases are idiopathic, but the condition may be acquired secondary to trauma, neoplasia or cystic malformations of the neurohypophysis. Although rare, there are a few reports of suspected hereditary CDI.

Congenital nephrogenic diabetes insipidus (congenital NDI)

NDI is a polyuric state caused by the reduced responsiveness of the renal tubules to anti-diuretic hormone. Acquired NDI occurs secondarily to a wide variety of disorders. Congenital NDI is an extremely rare condition of which there are only a few reports in the dog.

Congenital hypothyroidism

Congenital hypothyroidism occurs where there is a congenital defect in thyroid hormone production or transport and results in disproportionate dwarfism. It is suspected it may also be a cause of neonatal death or fading puppy syndrome.

Cushing’s syndrome

See Hyperadrenocorticism.

Diabetes mellitus

Diabetes mellitus occurs where there is hyper-glycaemia resulting from an absolute or relative lack of insulin. Where the blood glucose level exceeds the renal threshold, glycosuria results.

Hyperadrenocorticism (Cushing’s syndrome)

One of the most commonly diagnosed endocrinopathies in the dog, but rare in the cat. Hyperadrenocorticism occurs where there is a sustained and inappropriately elevated secretion of cortisol from the adrenal cortex. Hyperadrenocorticism may be pituitary dependent, where there is excessive adrenocor-ticotrophic hormone (ACTH) secretion leading to bilateral adrenal cortical hyperplasia and increased cortisol secretion, or it may be adrenal dependent where there is a unilateral or bilateral functional adrenocortical tumour.

Hypoadrenocorticism

Hypoadrenocorticism is a condition wherein there is inadequate adrenocortical hormone production leading to a deficiency in miner-alocorticoids and/or glucocorticoids. Primary hypoadrenocorticism (Addison’s disease) results most commonly from immune-mediated destruction of the adrenal cortices leading to deficiencies of all adrenocortical hormones. Whilst there is no apparent breed predilection, a hereditary factor has been suggested in some breeds. It is very rare in the cat.

Hypothyroidism

Hypothyroidism is a common endocrine disease in the dog. There is a deficiency in the secretion of thyroid hormone either as a result of thyroid gland destruction (primary hypothyroidism), inadequate pituitary production of thyroid stimulating hormone (TSH) (secondary hypothyroidism) or inadequate hypothalamic secretion of thyrotropin releasing hormone (TRH) (tertiary hypothyroidism). Many breeds seem predisposed to hypothyroidism, most notably Dobermann Pinschers and Golden Retrievers.

Immune-mediated destruction of the thyroid gland (Lymphocytic thyroiditis) is a common cause of primary hypothyroidism and has been demonstrated to be hereditary in laboratory Beagles and a family of Borzois.

Insulinoma

Insulinomas are functional insulin-secreting tumours of the pancreatic beta cells. Insulin secretion is independent of the normal negative feedback control, resulting in hypoglycaemia. These tumours are generally malignant with a high metastatic potential.

Lymphocytic thyroiditis

See Hypothyroidism.

Phaeochromocytoma

Uncommon in dogs and rare in cats, phaeochro-mocytomas are catecholamine-secreting tumours of the adrenal medulla. Most are slow-growing and benign, but some are malignant and may invade locally, and/or metastasise. The high level of circulating catecholamines produced results in hypertension and tachycardia.

Pituitary dwarfism

Pituitary dwarfism results from a failure of growth hormone secretion in an immature animal. The most striking abnormality is a failure to grow, animals remaining of small stature, but with normal proportional shape (proportionate dwarfism). There may be concurrent failure of other pituitary hormones (panhypopituitarism). The condition is most commonly seen in the German Shepherd Dog but has been identified in several other breeds.

Primary hypoparathyroidism

This is an uncommon condition, wherein lymphocytic plasmacytic destruction of the parathyroid glands results in a deficiency of parathyroid hormone and hypocalcaemia.

Primary hyperparathyroidism

Primary hyperparathyroidism is usually the result of a functional parathyroid adenoma (see also Parathyroid tumours under Neoplastic conditions). The excess of parathyroid hormone results in hypercalcaemia. The Keeshond seems particularly susceptible to the condition.

Thyroid neoplasia in dogs

Most thyroid tumours in the dog are invasive and malignant carcinomas presenting as readily detectable masses in the neck. Adenomas do occur but are usually small and rarely detected during life. Thyroid tumours in the dog are generally non-functional, only 5-20% being functional, producing clinical signs of hyper-thyroidism. Up to 30% of cases become hypothyroid as normal thyroid tissue is destroyed by the tumour. The remainder are euthyroid.