Pyelonephritis/ Perinephric abscess

I. What every physician needs to know.

Acute pyelonephritis is an infection of the upper structures of the urinary tract including the ureters, renal pelvis and renal parenchyma. The infection is usually due to bacteria ascending via the urethra into the bladder and collecting system. Eighty percent of cases of acute pyelonephritis are caused by Escherichia coli. Other causes include other members of the family Enterobacteriaceae, and enterococci.

Acute pyelonephritis is considered uncomplicated if the infection is caused by a typical pathogen in an immunocompetent patient who has normal urinary tract anatomy and renal function. Those who do not fit into this category are considered to have complicated acute pyelonephritis.

A perinephric abscess is a collection of infected material in the perinephric space. The infection usually is a result of the rupture of an intra renal abscess or chronic/recurrent pyelonephritis, especially in the setting of obstruction. It can also be due to hematogenous seeding of the renal parenchyma due to endovascular infection. Escherichia coli and other Enterobacteriaceae, and Staphylococcus aureus are the most common causes of perinephric abscesses.

II. Diagnostic Confirmation: Are you sure your patient has Acute Pyelonephritis/Perinephric Abscess?

Acute pyelonephritis patients present with fever, chills, flank pain and/or tenderness; and have a positive urinalysis, urine microscopy, and urine culture.

The diagnosis of a perinephric abscess can be difficult as the onset is often insidious. Symptoms can be similar as with pyelonephritis, however, typically do not resolve with empiric therapy alone. It often takes exam, laboratory data and radiologic data to make the diagnosis.

A. History Part I: Pattern Recognition:

Acute Pyelonephritis

Since acute pyelonephritis is an infection of the upper structures of the urinary tract the symptoms are more systemic than in a lower urinary tract infection. Patients can have a wide spectrum of presentation from a mild illness to sepsis.

Symptoms can include:

Fever
Chills
Flank pain/abdominal pain
Nausea and vomiting
Sepsis
Symptoms of cystitis – dysuria, urinary bladder frequency and urgency and suprapubic pain

One caveat of the above is the presentation of the elderly. They can be afebrile, but have other symptoms including alteration in mental status, as well as gastrointestinal or pulmonary complaints that predominate.

Perinephric Abscess

Perinephric abscesses present with a slower onset. Patients usually are ill for 2 or more weeks. Their presentation can be similar to acute pyelonephritis with:

Fever
Chills
Flank pain
Nausea and vomiting
Dysuria

B. History Part 2: Prevalence:

Acute uncomplicated pyelonephritis occurs in women. Risk factors for acute uncomplicated pyelonephritis in women include – recent sexual intercourse, use of a spermicidal agent or a diaphragm, and history of a previous urinary tract infection.

Acute complicated pyelonephritis can occur in both women and men. Risk factors for acute complicated pyelonephritis include:

1. Obstruction – enlarged prostate, nephrolithiasis, increased post void residual, neurogenic bladder

2. Immunosuppression – diabetes, sickle cell disease, organ transplant, human immunodeficiency virus, steroid use

3. Metabolic – nephrolithiasis, gout, hyperparathyroid

4. Anatomic or functional abnormality – single kidney, foreign body (stent, catheter), polycystic kidney, vesicoureteral reflux

5. Treatment – failure to respond, resistant organisms, recent invasive instrumentation

6. Other – pregnancy, extremes of age

Factors that predispose patients to perinephric abscesses include:

1. Obstruction – nephrolithiasis, increased post void residual, neurogenic bladder

2. Immunosuppression – diabetes, renal transplant, steroid use

3. Metabolic – nephrolithiasis

4. Anatomic or functional abnormality – polycystic kidney, vesicoureteral reflux

5. Treatment – recurrent or chronic urinary tract infections

6. Endovascular infection risk – chronic vascular access (i.e., dialysis, parenteral nutrition), intravenous drug abuse, prosthetic material, dental disease

C. History Part 3: Competing diagnoses that can mimic Acute Pyelonephritis and Perinephric Abscess.

The differential diagnoses for acute pyelonephritis and perinephric abscess is wide and includes diseases that can cause fever, chills and flank pain:

Cholecystitis
Appendicitis
Pancreatitis
Perforated viscus
Tubo-ovarian abscess
Ectopic pregnancy
Nephrolithiasis
Lower lobe pneumonia
Pelvic inflammatory disease
Urethritis
Prodrome of herpes zoster

D. Physical Examination Findings.

Physical exam for both acute pyelonephritis and perinephric abscess is usually positive for the following: fever, tachycardia, tenderness over the costoverterbral angles and abdomen on deep palpation.

Perinephric abscess can have a flank or abdominal mass as well.

E. What diagnostic tests should be performed?

There are no particular maneuvers that confirm the diagnosis but the presence of fever, tachycardia and tenderness over the costoverterbral angles and/or abdomen on deep palpation in absence of other findings points towards the diagnosis of acute pyelonephritis and/or perinephric abscess.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

The following tests should be done to confirm the diagnosis of acute pyelonephritis. If positive they point towards a diagnosis of acute pyelonephritis.

Urinalysis – positive for signs of pyuria which include nitrites and leukocyte esterase, can be positive for hematuria (nitrites are only present when infections are caused by the Enterobacteriaceae).
Urine microscopy – white blood cells, white blood cell casts, red blood cells.
Urine Gram stain – bacteria are seen.
Urine culture – 10,000 colony forming units (CFU) per cubic millimeter (mm³).
Complete blood count – elevated white blood cell count (WBC) is seen.
Blood cultures – only obtain if the diagnosis is in question, the patient is immunosuppressed or a hematogenous source is suspected.

The diagnosis of perinephric abscess is more difficult. The diagnosis is usually made based on radiologic studies. The following laboratory studies can be obtained:

Urinalysis – white blood cells and protein
Complete blood count – elevated WBC and possible anemia
Urine culture – can be positive, though potential false negatives if the abscess is isolated from the urinary stream
Blood culture – can be positive
Abdominal imaging via ultrasound or computed tomography (CT)

The main pitfall in the diagnosis of acute pyelonephritis and perinephric abscess is excluding other possible diagnoses. The following tests can be done to rule out other diagnoses that can present similarly. If positive they point away from the diagnosis of acute pyelonephritis and perinephric abscess.

Liver function tests
Lipase
Pregnancy test
Abdominal ultrasound
Pelvic ultrasound
Abdominal CT scan
Chest radiography (CXR)

Urine cultures can be negative in the setting of a perinephric abscess, especially if it is not continuous with the urinary drainage system. Ensure imaging is available to avoid missing the diagnosis.

Urine cultures can be falsely positive if poorly collected. Look for the full constellation of symptoms. A negative urinalysis and unusual symptoms should prompt an evaluation of alternative diagnoses.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

Renal ultrasound or non-contrasted abdominal CT via kidney ureter bladder protocol (CT KUB) can be used to evaluate the kidney in the setting of acute pyelonephritis. There are a few categories of patients who requiring imaging:

Those who have not responded to appropriate treatment within 48-72 hours should be imaged to evaluate for obstruction, abscess or complications of acute pyelonephritis.
Women with recurrent infections or a history or childhood infections or renal stones.
All men.
Any patient with clinical symptoms of obstruction or stones.
Severely ill patients.
Patients who have had recent instrumentation or procedures related to the urinary system.

Radiologic studies are the key to diagnosing perinephric abscesses:

CT with contrast – this is the preferred method of testing. It will identify the extent of the abscess and its relationship to the structures around it.
Magnetic resonance imaging (MRI) – will provide similar information as a CT scan with contrast, but is typically not used unless contrast is contraindicated.
Ultrasound – can potentially be performed quickly, at bedside, without contrast and radiation, however, may not be able to differentiate between abscesses and other structures.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.

None

III. Default Management.

The treatment of acute pyelonephritis can be divided into inpatient and outpatient treatment.

Those for whom inpatient treatment should be considered include patients with: persistent vomiting/inability to maintain hydration and take oral medication, progression of uncomplicated urinary tract infection (UTI), suspected sepsis, uncertain diagnosis, severe pain or debilitation, failure of outpatient treatment, lack of follow up or compliance, pregnancy, urinary obstruction, severe comorbid illness and any case of complicated acute pyelonephritis.

All others can be considered for outpatient treatment.

Outpatient treatment for acute pyelonephritis

Outpatient treatment for acute uncomplicated pyelonephritis consists of oral antibiotics. The Infectious Disease Society of America recommends:

1. Fluoroquinolone:

– First line treatment:

– Ciprofloxacin 500 milligrams (mg) twice day for 7 days, with or without an initial 400 mg dose of intravenous ciprofloxacin

– Levofloxacin 750 mg daily for 5 days

2. Trimethoprim-sulfamethoxazole:

– used if uropathogens in the area are known to be susceptible

– 160/800 mg twice a day for 14 days

3. Oral beta-lactam agents are less effective than other available agents for treatment of pyelonephritis. If an oral agent is used, an initial intravenous dose of ceftriaxone or aminoglycoside should be used. Amoxicillin-clavulanic acid:

– if allergy to the above medications

– 500/125 mg every 8 hours for 14 days

This outpatient therapy can be jump-started by a one-time intravenous dose of:

– 1 gram of ceftriaxone

– Consolidated 24 hour dose of an aminoglycoside (weight based)

Therapy should be tailored according to culture data as resistance to first-line antibiotics is increasing.

Inpatient treatment for acute pyelonephritis

Initial therapy for inpatient treatment for acute uncomplicated pyelonephritis should be based on local resistance data.

Antibiotic choices include:

1. Fluoroquinolone – Ciprofloxacin 400 mg intravenous (IV) every 12 hours

2. An extended spectrum cephalosporin – Ceftriaxone 1 gram IV every 24 hours

3. Carbapenem – Ertapenem 1 gram IV every 24 hours

4. Aminoglycosides with or without ampicillin

After initial inpatient treatment is started, local susceptibility data and/or urine culture data should be used to tailor antibiotics to complete a 10 to 14 day course.

Inpatient treatment for acute complicated pyelonephritis is the same as for acute uncomplicated pyelonephritis, and should consider treatment towards Pseudomonas which can include:

1. Cefepime 2 grams IV every 8-12 hours with or without an aminoglycoside

2. Piperacillin-Tazobactam – 3.375 – 4.5 grams IV every 6 hours with or without an aminoglycoside

Underlying urinary tract anatomic or functional abnormalities should be addressed.

After initial inpatient treatment is started, local susceptibility data and/or urine culture data should be used to tailor antibiotics to complete a 10 to 14 day course.

Treatment of perinephric abscesses

Treatment of perinephric abscesses requires drainage and antibiotic treatment.

Drainage should be done under CT or ultrasound guidance.

Empiric antibiotic therapy should cover broadly cover gram negative bacteria and Staphylococcal bacteria. Choices include the following for gram negative bacteria:

1. Cefepime 2 grams IV every 8-12 hours with or without an aminoglycoside

2. Piperacillin-Tazobactam – 3.375 – 4.5 grams IV every 6 hours with or without an aminoglycoside

Choices include the following for Staphylococcal bacteria:

3. Vancomycin – weight based or to target a trough of 10-15 micrograms/milliliter (mL) (15-20 micrograms/mL if critically ill or concern for abscess/deep-seated infection)

Once culture data has been obtained antibiotics should be tailored and continued for at least 2 weeks. Parenteral antibiotics may be needed to complete therapy especially if the infection is due to a drug resistant organism. If the infection is due to staphylococcal bacteremia, evaluation for endocarditis is essential.

In addition to the above care for admitted patient supportive care of symptoms can be provided:

1. Intravenous fluids (IVF) for dehydration

2. Medication for pain

3. Antiemetic medication for nausea and vomiting

A. Immediate management.

Immediate management for acute pyelonephritis includes:

For diagnosis – physical exam, blood work and urine tests as above.

For treatment – antibiotics and supportive treatment for other related symptoms such as nausea, pain and dehydration.

Immediate management for perinephric abscess includes:

For diagnosis – physical exam, blood work, urine tests and diagnostic imaging preferably via CT scan.

For treatment – antibiotics, drainage, and supportive treatment for other related symptoms such as nausea, pain and dehydration.

B. Physical Examination Tips to Guide Management.

There are no specific physical examination tips to guide management.

C. Laboratory Tests to Monitor Response To, and Adjustments in, Management.

For all patients, cultures should be used to guide antibiotic treatment.

For those patients hospitalized, temperature curve and WBC should be watched daily.

D. Long-term management.

Patients need to complete their antibiotic therapy for acute pyelonephritis. If they have recurrent infections further work up must be done to find the underlying cause.

Patients need to complete their antibiotics for perinephric abscess. They need imaging to make sure the infection has resolved.

E. Common Pitfalls and Side-Effects of Management.

Persistent symptoms for 48-72 hours should prompt an evaluation for causes of complicated pyelonephritis, obstruction or abscess. This evaluation can be done with renal ultrasound and/or CT KUB.

Most common side effects of management are the side effects of the antibiotics chosen to treat the infection.