Hyposthenuria in Cats
Hyposthenuria is a clinical condition in which the urine is chemically imbalanced. This may be due to trauma, abnormal hormone release, or excessive tension in the kidney.
The normal concentration and regulation of urine normally depends on an elaborate interaction between antidiuretic hormone (ADH), the protein receptor for ADH on the renal tubule (the tube that plays a role in the filtering, reabsorption, and secretion of solutes in the bloodstream), and excessive tension of the tissue within the kidney.
Abnormalities may also occur due to interference with the synthesis, release, or actions of ADH, damage to the renal tubule, and altered tension (tonicity) of the tissue within the kidney (medullary interstitium).
Symptoms will depend on the underlying cause of the disorder. Some of the more common ones include:
Any disorder or drug that interferes with the release or action of ADH, damages the renal tubule, causes medullary washout, or causes a primary thirst disorder.
Your veterinarian will perform a thorough physical exam on your cat, taking into account the background history of symptoms and possible incidents that might have led to this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis, with emphasis on determining the urine specific gravity.
The latter test reveals the functional capability of the kidney in its capacity to eliminate waste molecules without eliminating excess nutrients or water. These tests may confirm a urinary condition, with a low urine specific gravity of 1.000 to 1.006 g/ml, and excessive amounts of alkaline phosphates (ALP) in the blood serum, which would suggest hypoadrenocorticism or primary liver disease. High cholesterol is another common finding in cats with hyperadrenocorticism.
In cats suffering from pyometra (a disease of the uterus) or pyelonephritis (urinary tract infection), leukocytosis, a type of white blood cell, will be raised and will be present in the urine sample, along with abnormal amounts of protein in the urine, a condition called proteinuria. Proteinuria is common in patients with pyelonephritis, pyometra, and hyperadrenocorticism. If an underlying condition of pyelonephritis is present, the urinalysis will also show inflammatory sediment or bacteria in the urine (bacteriuria).
Other laboratory tests your doctor may want to conduct are adrenocorticotrophic hormone (ACTH) level checks in order to determine the cause of the hyperadrenocorticism, if found. That is, your veterinarian will want to distinguish a pituitary dependent versus an adrenal tumor. Visual imaging, using X-ray, may also be included to determine if the kidneys or surrounding urinary tract organs are damaged in any way. An intravenous pyelogram is the most accurate diagnostic technique for a visual examination of the kidneys, ureter, and urinary bladder. This is a minimally invasive procedure which uses an injection of contrasting material into the bloodstream, where it then collects in the kidneys and urinary tract and illuminates them on the X-ray.
An ultrasonography can be used to assess adrenal size, kidney and liver size and architecture, and uterine size (abnormal findings in the size of one or more of these organs may confirm an infection or reaction to infection). In addition, a magnetic resonance imaging (MRI) or computed tomography (CT) scan can be used to assess a pituitary or hypothalamic (which links the nervous system to the endocrine system via the pituitary gland) mass, which can be an associated cause of central diabetes insipidus or hyperadrenocorticism.
Treatment for the hyposthenuria will depend on the underlying disorder. Even if your cat is urinating excessively, or is having trouble making it to the litter box in time, do not restrict your cat's water intake unless it is appropriate to the definitive diagnosis and has been recommended by your veterinarian.
Living and Management
Your veterinarian will schedule follow-up visits to monitor your cat's urine specific gravity, hydration status, kidney function, and electrolyte balance. Dehydration is a possible complication with hyposthenuria, and can quickly become a life threatening condition, so care must be taken to ensure that your cat is properly hydrated at all times.