Pyelonephritis

Question 1

What is it?

Answer 1

Pyelonephritis refers to inflammation of the kidney resulting from bacterial infection. The inflammation affects the renal pelvis (join between kidney and ureter) and parenchyma (tissue).

Risk factors for pyelonephritis are:

Female sex
Structural urological abnormalities
Vesico-ureteric reflux (urine refluxing from the bladder to the ureters – usually in children)
Diabetes

Question 2

Causes?

Answer 2

Escherichia coli is the most common cause, as with lower urinary tract infections. E. coli are gram-negative, anaerobic, rod-shaped bacteria that are part of the normal lower intestinal microbiome. It is found in faeces and can easily spread to the bladder.

Other causes:

Klebsiella pneumoniae (gram-negative anaerobic rod)
Enterococcus
Pseudomonas aeruginosa
Staphylococcus saprophyticus
Candida albicans (fungal)

Question 3

Presentation

Answer 3

Diagnosis can be made clinically with a history and examination.

Patients have a similar presentation to lower urinary tract infections (i.e. dysuria, suprapubic discomfort and increased frequency) plus the additional triad of symptoms:

Fever
Loin or back pain (bilateral or unilateral)
Nausea / vomiting

Patients may also have:

Systemic illness
Loss of appetite
Haematuria
Renal angle tenderness on examination

Question 4

Investigations

Answer 4

Urine dipstick will show signs of infection, including nitrites, leukocytes and blood.

Midstream urine (MSU) for microscopy, culture and sensitivity testing is essential to establish the causative organism. The sample should ideally be collected before starting antibiotics.

Blood tests will show raised white blood cells and raised inflammatory markers (i.e. CRP).

Imaging may be used to exclude other pathologies, such as kidney stones or abscesses. This could be an ultrasound or CT scan.

Question 5

Management of Pyelonephritis

Answer 5

Referral to hospital if there are features of sepsis or if it is not safe to manage them in the community.

NICE guidelines (2018) recommend the following first-line antibiotics for 7-10 days when treating pyelonephritis in the community:

Cefalexin
Co-amoxiclav (if culture results are available)
Trimethoprim (if culture results are available)
Ciprofloxacin (keep tendon damage and lower seizure threshold in mind)

Patients admitted to hospital with sepsis require the sepsis six; with three tests and three treatments.

Three tests:

Blood lactate level
Blood cultures
Urine output
Three treatments:

Oxygen to maintain oxygen saturations of 94-98% (or 88-92% in COPD)
Empirical broad-spectrum IV antibiotics (according to local guidelines)
IV fluids

Two things to keep in mind with patients that have significant symptoms or do not respond well to treatment are:

Renal abscess
Kidney stone obstructing the ureter, causing pyelonephritis

Question 6

Chronic Pyelonephritis

Answer 6

Chronic pyelonephritis presents with recurrent episodes of infection in the kidneys. Recurrent infections lead to scarring of the renal parenchyma, leading to chronic kidney disease (CKD). It can progress to end-stage renal failure.

Dimercaptosuccinic acid (DMSA) scans involve injecting radiolabeled DMSA, which builds up in healthy kidney tissue. When imaged using gamma cameras, it indicates scarring or damage in areas that do not take up the DMSA. They are used in recurrent pyelonephritis to assess for renal damage.