Diabetes Insipidus in Dogs

Diabetes insipidus (DI) is a rare disorder that affects water metabolism, preventing the body from conserving water and releasing too much of it. This condition is characterized by increased urination, dilute urine (so-called insipid, or dull urine), and increased thirst and drinking. This disease is not related to diabetes mellitus (insulin diabetes).

Symptoms and Types

There are two main types of DI that affect dogs: neurogenic (or central diabetes insipidus) and nephrogenic diabetes insipidus. In neurogenic DI, the cause is due to a lack of the hormone vasopressin, which regulates the body's retention of water. The release of vasopressin is produced and regulated by the hypothalamus (in the brain), so a dysfunction in its release may be due to a head injury, or to a tumor in the brain. Vasopressin is produced in the hypothalamus into the connected pituitary gland, and is then released into the bloodstream. A lack of vasopressin may be due to a failure in the hypothalamus, or a failure in the pituitary gland. A significant number of cases is idiopathic.

Nephrogenic DI, meanwhile, can be caused by a deficiency of antidiuretic hormone (ADH), which functions to stimulate the capillary muscles and reduce the flow of urine, effectively conserving water for the body's various functions. The cause is found in the kidneys and their inability to respond appropriately to ADH, allowing too much water from the body to escape into the urine.

This is typically an acquired condition, and may be due to amyloidosis of the kidney, cysts on the kidney, or an imbalance of electrolytes.

Other common symptoms seen in dogs with DI include:

• Increased urination (polyuria)
• Increased drinking (polydipsia)
• Decreased urination with dehydration
• Housesoiling—occasional
• Poor hair coat 

Causes

Inadequate secretion of antidiuretic hormone ADH

• Congenital defect
• Unknown causes
• Trauma
• Cancer

Renal insensitivity to ADH

• Congenital
• Secondary to drugs
• Secondary to endocrine and metabolic disorders
  
  • Hyperadrenocorticism - overactive adrenal glands
  • Hypocalemia - low calcium levels in the blood
  • Pyometra - bacterial infection of the uterus
  • Hypercalemia - Increased levels of calcium in the blood
• Secondary to renal disease or infection
  
  • Pyelonephritis - bacterial infection of the kidneys
  • Chronic kidney failure
  • Pyometra - bacterial infection of the uterus

Diagnosis

Your veterinarian will perform a complete physical exam on your dog and ask you a series of questions to determine its state of health and the onset of symptoms. He or she will also order a blood chemical profile, a complete blood count, a urinalysis and an electrolyte panel.

Plasma ADH levels, for example, can be directly tested to differentiate between neurogenic, or central diabetes insipidus, and nephrogenic diabetes insipidus.

Magnetic resonance imaging (MRI) or computed tomography (CT), meanwhile, are useful for locating pituitary tumors and/or kidney disorders. A modified water deprivation test and/or an ADH supplementation trial can also be done to monitor body water loss.