Pyelonephritis: the relationship between infection, renal scarring, and antimicrobial therapy

A prospective study of children with first acute symptomatic E. coli urinary tract infection. Early 99mtechnetium dimercaptosuccinic acid scan appearances

Between 1985 and 1987 102 children, age 0-14 years, presented with a first acute symptomatic E. coli urinary tract infection. Investigations included early 99mtechnetium dimercaptosuccinic acid (DMSA) scan (which was performed at a median of 27 days), ultrasonography, micturating cysto-urethrography and indirect voiding radionuclide cystography using 99mTc DTPA. Follow-up DMSA scan was carried out after 6 months. Twenty-one of 102 of initial DMSA studies showed diminished uptake of radionuclide and 12 showed cortical scarring. Twenty-nine patients had significant vesicoureteral reflux (VUR). The finding of diminished uptake on the initial scan was significantly associated with fever, systemic upset, length of symptoms and a peripheral blood leucocytosis, (p less than 0.05). In addition the finding was associated with fever and loin pain in the older child. Both diminished uptake and scarring were more common in refluxing kidney units. We propose that, in children with UTI, diminished uptake on early DMSA scan localises infection in the renal parenchyma.

Relationship between neutrophil-mediated oxidative injury during acute experimental pyelonephritis and chronic renal scarring

Previous experiments with rats have suggested that pyelonephritic scarring after acute ascending Escherichia coli pyelonephritis partly results from excessive polymorphonuclear leukocyte (PMN) infiltration and activation in the kidney parenchyma. We have studied the role of PMN oxidative metabolism in generating tissue injury during acute pyelonephritis. Rats with acute pyelonephritis were treated with dapsone (25 mg/kg twice daily for 3 days), a compound known to prevent PMN oxidant damage. In vitro, levels of dapsone easily achieved in vivo inhibited myeloperoxidase (MPO)-mediated reactions involving the oxidation of halides to reactive cytotoxic hypohalites (such as MPO-mediated iodination and luminol-enhanced chemiluminescence). In contrast, dapsone had no effect on superoxide production, lysosomal enzyme release, or bacterial killing by activated PMN. In vivo, dapsone treatment had no significant effect on acute pyelonephritis with respect to (i) bacterial counts, (ii) inflammatory swelling, and (iii) PMN infiltration. However, dapsone-treated animals sacrificed 2 months after acute pyelonephritis had a 65% reduction of renal scars when compared with controls. Since dapsone had no antibacterial effect, this protection is compatible with the hypothesis that dapsone prevented oxidant-generated tissue injury due to the extracellular release of the MPO system by activated PMN during acute suppurative pyelonephritis.

99mTc dimercaptosuccinic acid (DMSA) scan in patients with established radiological renal scarring

The findings on 99mTc dimercaptosuccinic acid (DMSA) scans were examined in 54 patients aged 3 to 33 years in whom renal scarring had been diagnosed radiologically in childhood after urinary tract infection. There was no recent history of infection. Vesicoureteric reflux had been present in 48 patients and had stopped in 23 at the time of the DMSA scan. In six of the 72 radiologically scarred kidneys, the DMSA scan appeared normal but scarring would have been overlooked in only two of the 54 patients. DMSA scan changes are non-specific and underestimated individual scars in 21 kidneys. The intravenous urogram and the DMSA scan showed good correlation but should be regarded as complementary investigations in these patients, giving morphological and functional information, respectively. On DMSA scans the timing of any preceding urinary tract infection must be considered in order to differentiate diffuse potentially reversible defects in isotope uptake after urinary tract infection from those due to permanent renal scarring.

The inflammatory response and tissue damage. The example of renal scars following acute renal infection

Most clinical and experimental evidence suggests that renal scarring occurs following urinary tract infections in those patients with an abnormality of the urinary tract or kidney function. Experimentally, bacterial multiplication within the kidney occurs only in the presence of obstruction, leading rapidly to acute exudative pyelonephritis and invariably to kidney scars within weeks. Various manipulations of the bacterial load and/or of the inflammatory response during acute pyelonephritis have demonstrated that the inflammatory processes, not the bacterial component of pyelonephritis, are responsible for permanent renal tissue damage. Polymorphonuclear leucocytes (PMNLs) infiltrating the kidney tissue during acute pyelonephritis appear to release metabolites that are toxic to the parenchyma. Indeed, both the prevention of PMNL influx into renal tissue, by means of colchicine or cyclophosphamide, and the inactivation of some of their toxic metabolites, by means of dapsone, have led to the prevention of tissue damage and kidney scars. However, the most potent protective activity was observed with early antibiotic treatment, which stopped bacterial multiplication and prevented the early influx of PMNLs, thus preventing tissue damage and scar formation. Similar observations have been made in children with acute pyelonephritic episodes, in whom early and aggressive antibiotic treatment prevented subsequent kidney scars, while delayed treatment did not.

Vesico-uretero-renal reflux and the kidney

The most frequent complications of non-obstructive vesico-uretero-renal reflux (VUR) are segmental renal scars. These scars are confined to segments with intrarenal reflux which are, in addition, exposed to bacterial infection. Primarily, only gaping collecting duct orifices, confined to compound papillae and mainly situated at the kidney poles, allow intrarenal reflux. Scar contraction and obstruction seem to be able to transform closed collecting duct orifices into gaping ones, thereby enlarging the parenchymal area prone to intrarenal reflux and to renal scarring. Contrary to earlier reports, a recent survey has documented that new scars in children develop with significant frequency beyond 5 years of age. There is a greater tendency for scarring to develop with more severe VUR, but new renal scars can develop with all grades of VUR. Early and adequate antibiotic treatment decreases the extent of scarring. The results of experimental studies in which renal scarring developed in piglets with bladder decompensation resulting from intravesical obstruction but without bacterial infection may be relevant to the few children with proximal urethral valves and hypertonic neurogenic bladders but not to the large number with non-neurogenic detrusor instability or detrusor sphincter dyssynergia. Prospective studies have not shown different recurrence rates of urinary tract infections in medically managed compared with surgically managed children. The frequency of acute pyelonephritic attacks decreased significantly after operation.

Management of children with unobstructed urinary tract infection

There are two major considerations when taking care of children with urinary tract infection (UTI): firstly to prevent renal damage and secondly to relieve symptoms. A distinction should always be made between these two aims, since they often concern separate populations that may need different treatment and follow-up strategies. Acute pyelonephritis is a common disorder of infancy and early childhood which is easily overlooked. In all infants and children in whom the cause of fever is not apparent and in all those failing to thrive, urine should be examined by dip slide culture and by an estimation of leucocyte content. With adequate care the immediate and long-term prognosis of acute pyelonephritis is excellent. Thus prevention of kidney damage is mainly a matter of putting existing knowledge into practice. Uncomplicated recurrent lower UTI involves a low risk of renal damage. Short courses of antibiotic treatment easily eradicate most such infections but have no effect on the mechanisms underlying the susceptibility to recurrence. Single-dose therapy should be considered in such instances. Long-term antibiotic prophylaxis is mainly indicated in children with a high risk of renal scarring. Treatment is not recommended for children with asymptomatic bacteriuria.

Symptomatic recurrent urinary tract infections in patients with renal scarring in relation to fecal colonization with P-fimbriated Escherichia coli

We evaluated prospectively 49 women with renal scarring and a history of febrile urinary tract infections in regard to the incidence of recurrent symptomatic urinary tract infection and fecal colonization with P-fimbriated Escherichia coli. During a 3-year followup 26 patients (53 per cent) had symptomatic urinary tract infection (0.036 infections per patient-month), including 8 (16 per cent) who had 9 new episodes of febrile urinary tract infection, while 33 (67 per cent) had Escherichia coli bacteriuria (10(5) bacteria per ml. urine in pure culture). Thus, patients with previous febrile urinary tract infections and renal scarring have a high risk for recurrent infections. For comparison, the incidence of symptomatic urinary tract infection also was determined in 35 women with a recent episode of acute nonobstructive pyelonephritis and with normal kidneys on excretory urography. These patients had 0.031 symptomatic infections per patient-month. The fecal flora were examined twice a year for P-fimbriated Escherichia coli in 48 patients with renal scarring. Of these patients 21 (44 per cent) had at least 1 fecal colonization with a P-fimbriated Escherichia coli strain. However, in only 1 instance was a relationship detected between the presence of P-fimbriated Escherichia coli in the fecal flora and the development of subsequent febrile urinary tract infection. The findings indicate that fecal sampling twice a year is not of value to predict future urinary tract infections in adults with renal scarring.

Benefit from high intrarenal levels of gentamicin in the treatment of E. coli pyelonephritis

The importance of high intrarenal levels of gentamicin on the outcome of experimental pyelonephritis was studied in rats receiving either a short course (three days) of gentamicin (G) alone or combined with a longer course (14 days) of ampicillin (A), cephalothin (C), or trimethoprim (T), or two weeks of therapy with ampicillin, cephalothin, trimethoprim and gentamicin given alone. While ampicillin, cephalothin and trimethoprim were undetectable in the medulla within six hours of cessation of therapy, gentamicin was still detectable in levels six folds above the MIC up to six months after treatment had ceased. Six months after the end of treatment, the percentage of sterile left kidneys in animals treated with ampicillin (50%), cephalothin (15%), trimethoprim (20%) was lower than the percentage of animals receiving 14 days of gentamicin (100%), or the combinations AG:89%, CG:67% and TG:60%, P less than 0.01. Following three days of gentamicin, 50% of the left kidneys were sterilized. When compared to ampicillin, cephalothin or trimethoprim alone, combined therapies significantly reduced the number of CFU in the kidneys P less than 0.01. These combinations were almost as effective as two weeks of therapy with gentamicin. Short-term therapy (three days) with an aminoglycoside which concentrates in the renal parenchyma, combined with an antibiotic which will accumulate in other parts of the nephron, may result in "pharmacological synergy". This new approach to therapy of pyelonephritis may be promising.

Influence of inflammation on the efficacy of antibiotic treatment of experimental pyelonephritis

An acute exudative Escherichia coli pyelonephritis rat model was used to study the influence of progressive pyelonephritis on the efficacy of antibiotic treatment. In this model, transient ureteral obstruction after E. coli bladder inoculation induces early bacterial multiplication in the kidney parenchyma, and the bacterial counts peak by 48 h. The inflammatory response (assessed by the increase in kidney weight) is somewhat delayed, starting 36 h after inoculation and peaking by 72 h. Groups of rats received 4 doses over 48 h of saline, ceftriaxone (100 mg/kg), or ceftriaxone (100 mg/kg) plus gentamicin (4 mg/kg). These treatments were initiated 24, 36, 48, or 72 h after bladder inoculation. Antibiotic treatment started at 24 h was significantly more effective in reducing bacterial counts in the kidney parenchyma than at any later therapy onset. Only when started 24 h after inoculation was the synergistic combination of ceftriaxone plus gentamicin more effective in reducing bacterial counts than ceftriaxone alone. Ceftriaxone and ceftriaxone plus gentamicin regimens started at 24 h reduced significantly (by 42 and 55%, respectively) the incidence of acute exudative pyelonephritis when compared with the incidence in saline-treated controls. Early therapy onset (24 h) strikingly reduced the development of the inflammatory response. This reduction was less marked when antibiotic therapy was started at 36 h and no longer apparent when therapy onset was delayed up to 48 or 72 h. In conclusion, the efficacy of antibiotics in eradicating bacteria from the kidney parenchyma and in preventing acute exudative pyelonephritis was markedly hampered by the development of pyelonephritis.

Quantitative and qualitative effects of m-AMSA (amsacrine) on cellular immune components

The recently developed acridine derivative 4'-[(9-acridinyl)amino] methanesulphon-m-anisidine (m-AMSA) has become one of the preferred agents in the management of acute leukaemia but little is known of its effects on cellular immune components. We evaluated the qualitative and quantitative effects of m-AMSA on immune cell numbers and function, during both the leucopenic and myelorestorative phases, following intermittent high-dose therapy. Cell-mediated and inflammatory responses were depressed in the treated animals during the leucopenic phase but restoration of immune capability paralleled the recovery of circulating leucocyte numbers. Additionally, m-AMSA displayed unexpected immunomodulatory features: thymus-dependent antibody and delayed-type hypersensitivity responses were actually increased, suggesting the potential of m-AMSA as an immunoregulator in clinical and experimental studies.

Age as a main determinant of renal functional damage in urinary tract infection

Renal function was studied in 61 girls suffering from recurrent urinary tract infections, with at least one febrile infection. Clearance of inulin was determined. Intravenous urography and micturating cystourethrography were performed 1-6 months after the first infection and 0-6 months before or after the function test. A low glomerular filtration rate (GFR) was found only among children with their first pyelonephritis before the age of 3 years. A low GFR was found mostly in patients with small or scarred kidneys but was also seen in a few patients with normal intravenous urographs. Low GFR as well as radiologically small kidneys at the time of the function test were found independently of the presence or grade of vesicoureteral reflux at first infection. Patients with early onset pyelonephritis (before age 3 years) had a low capacity for early compensatory hypertrophy in contrast to patients with late onset pyelonephritis.

Infection-induced immunosuppression in pyelonephritis: characteristics of the suppressor cell(s)

Infection-induced suppressor cells may be associated with a depression of cell-mediated immune (CMI) mechanisms in pyelonephritis. In the present study, cell viability and cell to cell contact were established as prerequisites for immunosuppression and the role of mononuclear phagocytic cells and polymorphonuclear leukocytes, as immunoregulatory cells affecting CMI, was also examined. Fractionation of spleen cell suspensions was carried out using carbonyl iron, nylon wool, glass beads, and sephadex. These procedures restored mitogenic responsiveness to splenic lymphocytes from pyelonephritic animals, and it was possible to isolate cells with accessory and suppressor activity from nylon wool columns. Elutable cells (that is, cells which adhere to the column but could be recovered by the addition of EDTA) were characteristically accessory cells and increased the mitogenic responsiveness of normal lymphocytes. Adherent splenocytes which suppress mitogenic responses were isolated from pyelonephritic animals. Additionally, neutrophils, at concentrations readily demonstrable in lesions, depressed CMI responses in vitro. With this information available it should now be possible to carry out a detailed analysis of the cellular mechanism by which CMI in renal infection is depressed.

Scarring as a factor affecting the eradication of microorganisms from the kidney in pyelonephritis

The inability of antimicrobial agents to penetrate scarred renal tissue may explain some therapeutic failures. We examined the effect of scarring on antimicrobial therapy by using a unique animal model in which both kidneys were infected to the same degree but only one kidney was scarred. Scar formation could not explain the failure of ampicillin or nitrofurantoin to eradicate renal infection, but co-trimoxazole was less effective in the presence of tissue damage and scar formation than in their absence.

Effect of physiological manipulations on the chemotherapy of experimentally induced renal infection

The belief that a favorable physiological milieu in the urinary tract may augment the effectiveness of antimicrobial agents used to treat urinary tract infections was examined by using an experimental model of Escherichia coli-induced renal infection in rats. The effect of manipulating urinary pH and flow on the antimicrobial activities of gentamicin, carbenicillin, ampicillin, nitrofurantoin and co-trimoxazole was assessed. In addition, a potential synergistic effect of the sequential administration of gentamicin and cephalothin in the eradication of renal infection was investigated. Although significant physiological alterations were achieved, these did not affect the efficacy of the antimicrobial agents studied, and therapeutic failures were common.

Effect of iron on acute pyelonephritis and later chronic changes

Administration of iron to rats exacerbated early inflammatory changes of pyelonephritis produced by intravenous inoculation of Escherichia coli. This effect was noted with four of eight strains of E. coli tested and was dependent on bacterial inoculum. Despite this increase in severity of acute pyelonephritis as judged by numbers of bacteria in the kidney and careful gross and microscopic evaluation, there was no enhancement of chronic changes seen 6 months later.