Pyelonephritis (inflammation of the renal pelvis) is a bacterial infection of the renal pelvis that involves the kidney tissue. It is usually caused by bacteria that travel up through the urinary tract into the kidney. For this reason, it is usually accompanied by inflammation of the ureter and the bladder. In rare cases, pathogens reach the kidneys via the lymphatic system or the bloodstream, leading to what is known as excretory nephritis.
The pathogens that cause pyelonephritis through ascending urinary tract infections mainly include:
However, pyelonephritis can also develop from endometritis (=inflammation of the uterus, see related article) or prostatitis (=inflammation of the prostate, see related article) due to ascending bacteria.
In cases of discospondylitis (=inflammation of the intervertebral discs and adjacent vertebral bodies) or endocarditis (=inflammation of the inner lining of the heart), bacteria can enter the kidney via the lymphatic or bloodstream and thus lead to pyelonephritis.
In addition, there are various predisposing factors:
Pyelonephritis is often initially masked by an underlying condition such as urinary tract obstruction or diabetes. Symptoms that may be present, though not always, include:
If cystitis (=bladder inflammation, see related article) is also present, dysuria (=difficult, painful urination) may occur.
If toxins are no longer adequately excreted in the urine and accumulate in the body, uremia (=urine poisoning) develops. This can be recognized by a distinct, urine-like odor on the breath and skin. In the late stages, uremia leads to muscle cramps, neurological disorders, itching, high blood pressure, edema (=fluid retention), as well as impaired consciousness and even uremic coma.
After taking your initial history and performing a general examination, your veterinarian will conduct blood and urine tests. Based on the presence of kidney pain and fever, they can already make a preliminary diagnosis of acute pyelonephritis and distinguish it from a simple bladder infection. This is followed by ultrasound and/or X-ray examinations. In cases of doubt, an excretory urogram is performed, preferably via CT (see related article). For the excretory urogram, your veterinarian will administer a contrast agent into a vein. This is excreted via the kidneys, making the urinary tract visible on X-ray or CT images. In cases that remain unclear, a bacteriological examination of urine taken directly from the renal pelvis provides the necessary evidence. This is done via an ultrasound-guided fine-needle aspiration. This ensures that only bacteria from the renal pelvis are detected.
If acute pyelonephritis goes undiagnosed, it can develop into chronic pyelonephritis. The inflammation then heals through the formation of granulation tissue. The resulting scar tissue leads to what are known as shrunken kidneys, whose lumpy surface can be felt by your veterinarian. This is followed by blood and urine tests to assess remaining kidney function, as well as an ultrasound and/or X-ray examination to evaluate the size and structure of the kidneys.
Pyelonephritis is always considered a complicated urinary tract infection and is treated for six to eight weeks with regular monitoring of kidney function and electrolyte levels. Initially, the animal must be stabilized with intravenous fluids and, if necessary, pain medication. Treatment to combat the bacteria begins immediately after diagnosis with a broad-spectrum antibiotic administered intravenously (into a vein) and is then continued orally (administered by mouth). Following a bacteriological urine analysis with an antibiogram (a laboratory test to determine the bacteria’s sensitivity to various antibiotics), treatment should be switched from the broad-spectrum antibiotic to a specifically effective antibiotic. Bacteriological urine analyses are performed again one week after the start of therapy, as well as one and two months after the end of therapy. This ensures that the treatment was successful.
If necessary, surgical removal of a chronically bacterially infected kidney may be required. However, it must first be ensured that the other kidney is functioning adequately.
In addition, underlying diseases or factors must be treated or addressed.
The prognosis for pyelonephritis is favorable if it is detected early and any underlying conditions or risk factors are treated or eliminated. In advanced cases, the prognosis worsens significantly, as lost kidney function cannot be restored.
Since pyelonephritis often goes undetected in its early stages, annual checkups—including blood and urine tests—are of the utmost importance. If you notice any of the symptoms mentioned in your pet, take it to your veterinarian immediately for an examination. The earlier pyelonephritis is detected and treated, the lower the risk of serious complications.
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