Immune-Mediated Glomerulonephritis in Dogs

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 in two broad ways: immune-mediated and non-immune mediated.

• In immune-mediated cases, immune complexes (mixtures of antibodies and antigens) are filtered out of the bloodstream and become trapped in the glomeruli. When these complexes are trapped, the body responds by activating its immune defenses, resulting in further damage to the glomeruli.
• In non-immune mediated cases, the damage to glomeruli is not caused by immune complexes.

This handout focuses on immune-mediated glomerulonephritis.

What are glomeruli?

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. 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 stimulates the immune system for long periods of time can cause glomerulonephritis. Some possible causes include:

• Chronic periodontal (dental) disease
• Cancer
• Heartworm infection
• Ehrlichia infection (a tick-borne disease)
• Lyme disease (a tick-borne disease)
• Pyometra (a bacterial infection in the uterus)
• Endocarditis (a bacterial infection in the heart, often secondary to periodontal disease)
• Chronically inflamed skin
• Immune-mediated diseases (such as lupus)
• Chronic pancreatitis (inflammation of the pancreas)
• Prostatitis (inflammation of the prostate)

In many dogs with glomerulonephritis, the cause cannot be found, and the problem is considered idiopathic (unknown origin).

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. Early signs of protein loss may include nonspecific symptoms, like 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 in the lungs), and peripheral edema (swelling of the limbs). Dogs with nephrotic syndrome have high blood pressure and may develop abnormal blood clots.

Chronic, severe glomerulonephritis can lead to the development of chronic kidney disease (CKD). Symptoms seen in dogs with CKD include lethargy, vomiting, increased drinking, and increased urination.

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 routine urinalysis. The urine may also contain hyaline casts, which are proteins 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; the chemistries will also look for evidence of kidney failure (buildup of waste products)
• 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 (not always performed) to identify glomerulonephritis conclusively and to differentiate it from amyloidosis, which is another kidney disease that affects the glomeruli

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 depends on the underlying infectious, inflammatory, or cancerous disease that is causing the immune system to create immune complexes that are being trapped in the glomeruli. Unfortunately, in many glomerulonephritis cases, no underlying disease can be identified, or if one can be identified, it cannot be cured.

Your veterinarian will recommend the best treatment plan for your dog. Some of the prescribed treatments for glomerulonephritis may include:

• Immunosuppressive drugs to suppress the immune complex formation (generally only used if a kidney biopsy identified an active immune component)
• Anti-clotting agents or a low dose of aspirin, to prevent clotting in the glomeruli
• Omega-3 fatty acid supplementation to help reduce the inflammatory response and prevent clotting
• Specialized prescription diets (in pets with kidney failure or hypertension)
• Angiotensin-converting enzyme (ACE) inhibitors such as enalapril (Enacard®) or benazepril (Fortekor®), to minimize protein loss in the urine and to help control blood pressure
• 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®) to control high blood pressure
• If nephrotic syndrome is occurring, then diuretics such as furosemide (Lasix®) may be required, and it may be necessary to drain fluid from the abdomen or lungs

What is the prognosis for glomerulonephritis?

The prognosis for glomerulonephritis is based on your dog’s specific condition and severity. In general, glomerulonephritis is a potentially serious condition that requires extensive diagnostic tests and treatments. Your veterinarian will discuss a diagnostic and treatment plan for your dog to help you manage this serious condition.