Acute pyelonephritis

Acute pyelonephritis is more common in females, especially during childhood, at puberty, soon after marriage (as a complication of ‘honeymoon cystitis’), during pregnancy and during menopause. It occurs more on the right and is frequently bilateral.

Clinical features

There may be prodromal symptoms of headache, lassitude and nausea but the onset of pain is usually sudden, often with a rigor and vomiting. There is acute pain in the flank and hypochondrium. In a few cases the pain resembles renal colic. The temperature rises to 38.8 or 39.50C and is remitting. The symptoms of cystitis set in soon after the onset with urgency, frequency and scalding dysuria. On examination, there is tenderness in the hypochondrium and in the loin. Rarely in cases of severe bilateral pyelonephritis, especially when there is an associated obstruction, the damage to renal function may be sufficient to cause uraemia.

Bacteriological examination of the urine

A midstream urine should be collected into a sterile container; the urine is centrifuged and the sediment examined microscopically. In early acute pyelonephritis there are usually a few pus cells and many bacteria. The macroscopic appearance of the urine may be misleadingly clear, until the infection becomes established when the urine is cloudy and full of pus. Culture and sensitivity testing of the causative organisms allows a rational choice of antibiotic, but parenteral treatment with a broad-spectrum antibiotic should be started before the results are available.

Severe cases

There are repeated rigors and the temperature rises to 400C or more, often without a corresponding rise in pulse rate. There is vomiting, sweating and thirst; the patient feels awful. The blood culture is usually positive, especially if the specimen has been taken during a rigor.

Differential diagnosis

When the symptoms and signs are typical the diagnosis is straightforward. In other circumstances it may be difficult to be sure that the patient does not have pneumonia, acute appendicitis or acute cholecystitis. The urgent need is to distinguish acute pyelonephritis from appendicitis, and the site of pain and the presence of marked peritonism are usually helpful in identifying the latter. A plain abdominal radio­graph may show the outline of a swollen kidney and, if the infection is severe, a skilled ultrasonographer may be able to detect the typical appearances of pyelonephritis.

Pyelonephritis of pregnancy

Pyelonephritis of pregnancy usually occurs between the fourth and sixth month of gestation in women who have a past history of recurrent uri­nary infection. In about 10 per cent of cases the disease runs a severe and protracted course and occasionally leads to abortion or premature birth.

Urine infection in childhood

Urine infection in childhood is important to recognise because it may endanger the function of the growing kidney. In young children, there may be few symptoms but the child passes cloudy or offensive urine. The possibility of urinary sepsis should always be considered if a child fails to thrive, fails to eat or suffers unexplained pyrexia. Pain or screaming on micturition may occur. The older child may complain of loin pain and may develop urinary frequency and nocturnal incontinence.

Up to 50 per cent of children with urinary infection have an under­lying anatomical abnormality. Once the diagnosis has been confirmed by examination of a clean-catch specimen or by a specimen obtained by suprapubic needle puncture, a full urological investigation is essential.

Vesicoureteric reflux of urine is detectable in about 35 per cent of children with recurrent urinary infection. In some patients the reflux is caused by high pressure in a neuropathic bladder. It may be intermittent and is often more marked when there is active infection. Renal damage results from the combination of reflux and urinary infection early in life and reflux nephropathy is the most common cause of end stage renal failure in the UK. Once the diagnosis has been confirmed by micturating cystography, the urine should be cleared by means of an appropriate antibiotic. Long-term prophylactic antibiotic treatment has become the favoured treatment for recurrent urinary infections resulting from reflux. Surgical reimplantation of the ureters is reserved for those in whom conservative measures fail. Reimplantation in these patients often fails to cure reflux.

Acute pyelonephritis associated with urinary retention

Acute pyelonephritis is a relatively uncommon complication of chronic urinary retention. Often the organisms are introduced during instrumentation and, in the days of unsterile catheterisation, the condition was known as ‘surgical kidneys’. Patients who have significant post-micturition urinary residue should be given prophylactic antibiotics to cover transurethral procedures.

Treatment of acute pyelonephritis

The treatment of acute pyelonephritis should be prompt, appropriate and prolonged. A full investigation to exclude underlying abnormalities in the urinary tract should be undertaken as soon as the attack is controlled.

The patient will usually feel like lying in bed. While awaiting the bacteriological report and the results of sensitivity tests, an antimicrobial with a wide range of activity, such as amoxycillin or gentamicin, should be administered, parenterally if necessary. If the urine is acid, as it is in the common coliform infections, alkalinisation of the urine by potassium citrate may help by inhibiting the growth of these organisms and relieving dysuria. When pain is severe a morphine-like analgesic drug may be necessary if nonsteroidal anti-inflammatory agents are not effective. The patient should be encouraged to drink copiously; if this is not possible because of nausea and vomiting, an intravenous infusion should be set up.

Most urinary infections acquired outside hospital are sensitive to relatively cheap agents such as trimethoprim and amoxycillin. Hospital-acquired infections are much more likely to be resistant and more expensive second-line antibiotics may be needed. Gentamicin and carbenicillin are suitable for combating infections with more resistant strains of Pseudomonas pyocyanea, Proteus sp. and Klebsiella sp. Ciprofloxacin is particularly useful against Pseudomonas sp. in patients who do not have septicaemia. Despite the efficacy of modern antibacterial drugs, recurrent infection is likely if there is an untreated underlying abnormality of the urinary tract such as a stone, vesicoureteric reflux or retention of urine.