Discussion
The first case of gas-forming renal infection was described by Kelly and MacCullum in 1898, though it was not until 1962 that Schultz and Klorfein used the term 'emphysematous pyelonephritis' to describe a spectrum of disease processes that result in the production of gas in the renal parenchyma. The gas can be focal or diffuse, and can spread to the collecting system or track into the perinephric and paranephric spaces. Although uncommon, with only a few hundred cases reported in the medical literature, the condition is associated with significant morbidity and mortality. Mortality from EPN is primarily attributable to sepsis, and despite improvements in the management of this condition over the past two decades, remains high at 21%. Up to 90% of patients who develop EPN have poorly controlled diabetes mellitus. Other reported factors associated with the development of the condition include alcohol and substance misuse, polycystic kidney disease and immunological impairment. The incidence of EPN is much higher in females than in males, with increased susceptibility to urinary tract infection in females being the most likely explanation for this. Although reported worldwide, EPN appears to be geographically commoner in Asia, with a higher proportion of case reports coming from there. Factors involved in the pathogenesis of this condition include the triad of (1) high levels of glucose within the tissues (2) the presence of gas-forming bacteria, and (3) impaired tissue perfusion, which facilitates anaerobic metabolism. Gram-negative facultative anaerobic bacteria ferment glucose and lactate. This results in the formation of high levels of carbon dioxide and hydrogen which accumulate at the site of inflammation. The majority of patients with EPN present in their fourth or fifth decade, with symptoms suggestive of pyelonephritis such as dysuria, fevers, rigors, nausea, vomiting and flank pain. The commonest physical sign is loin tenderness. Diagnosis of EPN is made radiologically. A plain radiograph of the abdomen may show an abnormal gas shadow in the renal bed raising suspicion of the condition, and CT will confirm the presence of intrarenal gas and define the extent of EPN. Initial management includes resuscitation, optimisation of glycaemic control and treatment of sepsis with appropriate antibiotics. It is important to maintain a systolic blood pressure of > 100 mmHg, with fluid resuscitation or inotropes if required. Gram negative bacteria such as Escherichia coli and Klebsiella pneumoniae remain the commonest causative organisms, so the initial antibiotic regimen should target these. Until the late 1980s the accepted treatment of EPN was emergency nephrectomy or open surgical drainage together with antibiotic therapy, resulting in a reported mortality rate of 40–50%. Significant advances in percutaneous catheters have made PCD a possible treatment option. PCD should be performed on patients who have localised areas of gas and in whom functioning renal tissue is present. The drainage tubes should stay until follow-up CT shows resolution of the EPN features, and until then, if necessary, the tube can be flushed with antibiotic solutions.