What is glomerulonephritis?
Glomerulonephritis, also known as glomerular nephritis (GN), is a type of renal (kidney) disease characterized by inflammation of the glomeruli. Glomeruli are tiny structures in the kidneys that act as filters for the blood. Glomerulonephritis occurs when immune complexes (mixtures of antibodies and antigens) are filtered out of the bloodstream and become trapped within the glomeruli. When these compounds are trapped, the body responds by activating its immune defenses, resulting in further damage to the glomeruli.
What are glomeruli?
The glomeruli are microscopic structures in the kidney that filter toxins (waste products of normal bodily functions) out of the blood. The role of the glomeruli is to remove all the small metabolic toxins from the bloodstream and leave the larger molecules (specifically blood proteins) in the blood where they belong. The filtration of these waste materials is the first step in the formation of urine. Additional filtering occurs in the kidney tubules where electrolytes, such as sodium and potassium, are conserved or excreted as needed. There are millions of glomeruli within the kidneys. When these structures are damaged, kidney function is greatly impaired and toxins build up in the body, causing serious illness.
What causes glomerulonephritis?
Any condition that causes chronic stimulation of the immune system resulting in the formation of immune complexes can cause glomerulonephritis. Some possible causes include:
- chronic periodontal (dental) disease
- heartworm infection
- feline leukemia virus (FeLV)
- feline immunodeficiency virus (FIV)
- feline infectious peritonitis (FIP)
- pyometra (a bacterial infection of the uterus)
- endocarditis (bacterial infection in the heart, often secondary to periodontal disease
- chronically inflamed skin
- immune-mediated diseases (such as lupus erythematosus or discoid lupus)
- chronic pancreatitis
In many cats with glomerulonephritis, the cause cannot be found, and the problem is considered to be idiopathic (unknown).
What are the clinical signs of glomerulonephritis?
Since the filtering ability of the glomeruli is impaired, there is usually an elevated amount of protein in the urine and a reduced amount of protein in the blood. Due to this loss of protein, mild to moderate clinical signs may include such non-specific symptoms as weight and muscle loss.
More severe clinical signs are referred to as nephrotic syndrome and include fluid in the abdominal cavity (ascites), increased respiratory effort (due to fluid within the lungs), and peripheral edema (swelling of the limbs). Many cats with glomerulonephritis will be lethargic with anorexia (poor appetite) and weight loss. Many will have increased thirst and urination; intermittent vomiting is also very common. Approximately 70% of patients will eventually develop chronic renal failure.
Some cats will demonstrate no clinical signs, and the only early evidence of this disease will be an elevated amount of protein on a routine urinalysis.
"Approximately 70% of patients will eventually develop chronic renal failure."
Some cats may develop symptoms related to thromboembolism (a sudden blockage of a major blood vessel by a blood clot). Vessels commonly blocked include arteries in the lungs, which cause rapid breathing or panting, rapid heart rate, and high body temperature; and the iliac arteries (which supply the back legs), which causes a blockage called a saddle thrombus, with sudden paralysis of the rear limbs. A thromboembolism is a medical emergency and, if you see these symptoms, you should take your cat to your veterinarian immediately.
What is nephrotic syndrome?
Nephrotic syndrome is defined as the combination of significant protein loss in the urine, high serum cholesterol, low serum albumin (serum is the fluid portion of the blood), edema (swelling), or other abnormal accumulation of fluid. Patients with nephrotic syndrome have high blood pressure and may develop abnormal blood clots, resulting in a variety of signs associated with blocked blood vessels, or edema, especially of the legs or abdomen.
How is glomerulonephritis diagnosed?
In most cases, urine tests are sufficient to presumptively diagnose the presence of glomerular disease. Significant proteinuria (protein loss in the urine) is typically found on a routine urinalysis. Often the urine will also contain hyaline casts, which are proteins that are in the shape of the renal tubules, indicating damage to those structures. A urine culture is helpful to eliminate bladder infection as a cause of proteinuria. A test called a urine protein to creatinine ratio (UPC) can be performed on the urine sample to determine the actual amount of protein loss.
Other tests that are necessary to complete the diagnostic workup include:
- complete blood count (CBC) to identify anemia, inflammation, infection, or low platelet count
- serum chemistry tests to identify low blood protein concentration and high blood cholesterol concentration
- blood pressure measurement to identify systemic hypertension
- radiographs (X-rays) or ultrasound of the kidneys to search for obvious masses or abnormal kidney shape and size
- kidney biopsy to identify glomerulonephritis conclusively and to differentiate it from amyloidosis, which is another kidney disease affecting the glomeruli
To summarize, there are many tests required to diagnose glomerulonephritis accurately, and it can take several days to a few weeks to complete the necessary diagnostic workup.
How is glomerulonephritis treated?
"The ideal treatment for glomerulonephritis is determined by identifying the underlying infectious, inflammatory, or cancerous disease..."
The ideal treatment for glomerulonephritis is determined by identifying the underlying infectious, inflammatory, or cancerous disease that is causing the immune system to create the immune complexes that are being trapped in the glomeruli. Unfortunately, in as many as 75% to 80% of the cases with glomerulonephritis, no underlying disease process can be identified or, if one can be identified, it cannot be cured. Your veterinarian will recommend the best treatment plan for your cat.
Some of the prescribed treatments for glomerulonephritis may include:
- immunosuppressive drugs to suppress the immune complex formation
- a very low dose of aspirin to prevent clotting within the glomeruli
- omega-3 fatty acid supplementation to help reduce the inflammatory response and prevent clotting
- specialized diets may be used in some instances (low protein, low phosphorus diets should be fed to pets in kidney failure; low sodium diets should be fed to pets with hypertension)
- angiotensin-converting enzyme (ACE) inhibitors, such as enalapril (Enacard®) and benazepril (Fortekor®), or angiotensin receptor blockers such as telmisartan (Semintra®) to minimize protein loss in the urine and to help control blood pressure
- blood pressure medications, such as amlodipine (Norvasc®) or telmisartan, to control high blood pressure
What is the prognosis for glomerulonephritis?
The prognosis for glomerulonephritis is based on your cat's specific condition and severity. In general, this is a potentially serious condition requiring extensive diagnostic testing and treatments. Your veterinarian will discuss a diagnostic and treatment plan for your cat to help you manage this serious condition.