Glomerulonephritis remains an important cause of renal disease in dogs

Glomerulonephritis remains an important cause of renal disease in dogs

Mar 01, 2004

Q: How does one diagnose and manage dogs with glomerulonephritis?

Johnny D. Hoskins, DVM, Ph.D., Dipl. ACVIM
A: Dr. Shelly L. Vaden at the 21st American College of Veterinary Internal Medicine Forum in Charlotte, North Carolina, gave a lecture on diagnosis and treatment of glomerulopathy in dogs. Some relevant points in this lecture are provided.

Glomerular disease is an important cause of renal disease in dogs. The incidence of some forms of glomerular disease may increase with age. There are both immunologic and non-immunologic mechanisms of glomerular injury that can lead to the various forms of glomerular disease. Glomerulonephritis is generally considered to be the most commonly occurring glomerular disease in dogs and is the result of immunologic glomerular injury. Immune-complexes that have become deposited in the glomerulus or have formed in-situ initiate glomerular damage.

Cell-mediated immune mechanisms also take part in the pathogenesis of glomerular inflammation. Once glomerular damage is initiated, the activation of complement, the coagulation cascade and resident cells, influx of neutrophils, monocytes and platelets, release of proteolytic enzymes, synthesis of cytokines or other growth factors, generation of proinflammatory lipid mediators and alteration of hemodynamic factors contribute to glomerular injury.

It can be very difficult to differentiate non-immunologically from immunologically mediated glomerular diseases with the limited diagnostic techniques that are generally used in the evaluation of proteinuric dogs.

In general, there is no gender predisposition for glomerular disease in dogs; however, the clinical manifestations of X-linked hereditary nephritis are more severe in affected male dogs. Glomerular disease can develop in any age dog but appear to be more common in middle-aged to older dogs.

There are several breeds of dogs known to have familial glomerular diseases; some of these diseases are manifested at an early age (Bernese Mountain dog, Bull Terrier, Cocker Spaniel (especially English), Dalmatian, Doberman Pinscher, Newfoundland, Chinese Shar-pei, Soft-Coated Wheaten Terrier).

Dogs with glomerulopathies may be asymptomatic, may have non-specific signs of disease (weight loss, lethargy), or may present with signs consistent with chronic renal failure or uremia (polyuria, polydipsia, anorexia, vomiting, malodorous breath). Signs of fluid retention (abdominal enlargement consistent with ascites, subcutaneous edema) or thromboembolism (dyspnea, decreased or absent peripheral pulse, loss of limb function) will occasionally be the primary complaint at presentation. Other dogs may have non-specific evidence of systemic disease such as poor body condition or poor hair coat. Dogs with advanced disease may have oral ulcerations and pale mucous membranes.

Proteinuria says glomerular disease Historically, a urine protein: creatinine ratio (UPC) >1 in a urine sample that is free of macroscopic hematuria or inflammation has been considered abnormal. However, the UPC in healthy dogs probably does not exceed 0.5. There is no magic value of UPC that is diagnostic for any one disease. Dogs with amyloidosis, in general, have the highest UPCs while those with tubulointerstitial disease have normal values or values that are in the lower part of the abnormal range.

Dogs with glomerulonephritis can have UPCs as low as 1 or in excess of 40. Microalbuminuria is detected prior to increases in UPC, and the magnitude of microalbuminuria increased over time in dogs that eventually developed overt proteinuria as detected by increased UPC.

A dog with persistent microalbuminuria of increasing magnitude should be assessed as having an injurious process to the glomerular filtration barrier and may eventually develop overt proteinuria.

Isosthenuria is a variable finding in dogs with glomerulopathies; the urine concentrating ability remains intact in many dogs. In dogs with glomerular disease, casts, if present, are most often hyaline but can be granular, waxy or fatty. Other abnormal findings may include hypoproteinemia due to hypoalbuminemia, hypercholesterolemia, azotemia, hyperphosphatemia and nonregenerative anemia.

Thrombocytosis is common. Antithrombin III activity is predictably decreased in dogs that have a serum albumin of less than 2.0-2.5 g/dl. Probable risk factors for thromboembolism in dogs include serum albumin <2.0 g/dl and antithrombin III <70 percent of normal.

The kidneys may look normal on abdominal radiography or appear small and irregular. Some dogs may have enlarged kidneys. Similar changes in shape and size can be seen by ultrasound but increased echogenicity of the cortex and loss of corticomedullary distinction may also be noted.

The renal pelvis may be mildly dilated if polyuria is present or fluids are being given. The kidneys may appear normal by ultrasound. During radiographic or ultrasonographic evaluation of the abdomen, attention should also be given to other organs in search of another disease process. Thoracic radiographs should also be evaluated in middle to advanced age dogs.

Hypertension is common in dogs with glomerulopathies. Uncontrolled hypertension is a risk factor for progressive renal injury. Every dog with persistent proteinuria should have blood pressure measured on a regular basis (every three to six months). Renal biopsy provides a definitive diagnosis of glomerular disease but may not be needed if treatment of a potential underlying disease leads to resolution of the proteinuria. When renal biopsies are required in the diagnostic evaluation of dogs with glomerular disease, tissue specimens should be submitted for light microscopy.