Page 271 - Medicine and Surgery

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Chapter 6: Urinary tract infections 267

Acute pyelonephritis Blood culture.
Renal USS and plain KUB X-ray may be performed

Definition
if response to treatment is slow, or in suspected com-
Acute upper urinary tract infection, which causes in-
plicated cases, to exclude any underlying renal tract
flammation of the interstitium of the kidney.
abnormality, and the presence of stones. If there is any
evidence of obstruction this requires rapid drainage
Aetiology (see page 256). Some stones are not radio-opaque,
Bacterial infection, either ascending from the lower uri- and will be missed with these tests, in which case an
nary tract or, less commonly due to haematogenous IVU or CT scan is more definitive.
spread in bacteraemia or septicaemia. The most com-
mon organism is E. coli,as for other UTIs.
Management
Mild cases may respond to oral antibiotics as for urinary
Pathophysiology
tract infection, but many require intravenous therapy
Predisposing factors to ascending infection include
suchasgentamicinandciprofloxacin.Inhospitalisedpa-
pregnancy (progesterone dilates the ureters), diabetes
tients, once clinically improving and able to tolerate oral
mellitus (does not increase incidence of UTI’s but does
medications, i.v. antibiotics and fluids can be converted
seem to make them more likely to be severe), urinary
to oral. Antibiotics should be tailored to the sensitivity
stasis due to obstruction, dilatation or neurological
and specificity, and continued for 10–14 days (longer
causes and reflux.
courses in patients who were more unwell, complex, im-
munosuppressed or responded slowly).
Clinical features
Fever >38 C, rigors, loin pain and tenderness with or
◦
withoutlowerurinarytractsymptoms.Nauseaandvom-
iting are common. Features may be less specific in the Renal or perinephric abscess
elderly.
Definition
An abscess that forms in the kidney, or in the perinephric
Macroscopy/microscopy fat,astheresultofascendinginfectionorhaematogenous
The kidneys appear hyperaemic, and tiny yellow-white spread. These have become less common, due to more
spherical abscesses may be seen in the cortex. There is effective antibiotic treatment of pyelonephritis.
neutrophilic infiltration, and bacteria may be seen.
Aetiology
Complications
As with other urinary tract infections, the most common
Gram negative septicaemia causing shock is uncom-

organisms are E. coli and Staphylococcus.
mon in young, otherwise healthy patients, but may
lead to multiorgan failure. Necrotic renal papillae due
to inflammatory thrombosis of the vasa recta, can be Pathophysiology
shed, causing obstruction and acute renal failure. Commonly the infection ascends via the lower urinary
Recurrent infections cause renal scarring and im- tract to cause pyelonephritis. In most cases, there is an

paired renal function, which may cause hypertension. underlying renal abnormality such as reflux, stone(s) or
See also perinephric abscess (see below). apolycystic kidney that predisposes to a focal area be-

coming walled off to form an abscess. Haematogenous
Investigations spread accounts for ∼25% of cases, e.g. in infective en-
Urine microscopy and culture. Urinalysis is usually docarditis, or other cause of bacteraemia. Perinephric

abnormal, but may not be grossly so. abscesses may arise due to infection spreading from the
FBC and differential. U&Es and creatinine (assess hy- kidney into the perinephric fat, or by direct haematoge-

dration and renal function). nous spread.