What is Pyelonephritis?

Pyelonephritis is an inflammatory disease of the kidneys (or one kidney) of an infectious origin with a predominant localization of the pathological process in the interstitial tissue and an obligatory lesion of the pyelocaliceal system. With the spread of infection in an ascending way, the pelvis-pelvic system is first involved in the inflammatory process, and then the interstitial tissue of the kidneys. With hematogenous infection, the interstitial tissue is affected earlier, and then the inflammatory process spreads to the cups and pelvis. According to modern concepts, there is no isolated lesion of the pelvis (pyelitis), since the inflammatory process always (in some cases earlier, in others later) passes to the interstitial tissue of the kidney.

The localization of the inflammatory process is possible only in the interstitial tissue of the kidneys without spreading it to the cups and pelvis. In such cases, the term “interstitial nephritis” is used, which, although widely used in clinical practice, is used in a narrower sense than the term “pyelonephritis.” However, it is possible that with a prolonged course of interstitial nephritis, the inflammatory process from the interstitial tissue can spread to the cups and pelvis and, consequently, lead to the development of pyelonephritis.

Pyelonephritis is widespread among adults and children, characterized by a long duration of the course, significant disability and a possible adverse outcome. Along with glomerulonephritis, this is one of the most common causes of chronic renal failure.

Among all human diseases, pyelonephritis is second in frequency after acute respiratory diseases and first among kidney diseases (A.P. Peleshchuk, 1974; A. Ya. Pytel, S.D. Goligorsky, 1977; data from WHO and others). The incidence of pyelonephritis, especially acute, has increased markedly, which is associated not only with an improvement in the diagnosis of this disease, but also with an increased virulence of microbes, an increase in their resistance to antibiotics and other antimysrobic agents. Among all inpatients, people with pyelonephritis account for O, 6% (A. Ya. Pytel, 1977), among patients in the therapeutic departments – 6%, and among kidney patients – from 30% (G. P. Shultsev, V. I Burtsev, 1975) up to 58% (A. G. Bryukhovetsky, 1991). According to pathological data, pyelonephritis is found in 6-16-20% (G. Majdrakov, 1973; X. Dutz, 1968; N. Sarre, 1966 and others), and as the main cause of death, in 2.5% (I. A. Borisov, V.V. Sura, 1982) and 5.6% (A. Ya. Pytel, S. D. Goligorsky, 1977) of all autopsy.

Despite the increased diagnostic capabilities, it is difficult to recognize pyelonephritis in vivo. This leads to a high frequency of errors in the diagnosis of this disease, especially in outpatient conditions (from 30 to 50%). Even in specialized medical institutions, the patient is first diagnosed with the correct diagnosis only in 30% of cases (A. Ya. Pytel, S. D. Goligorsky, 1977). In this regard, patients with pyelonephritis often pass under other diagnoses, such as hypertension. Sometimes pyelonephritis develops in patients with glomerulonephritis, diabetes mellitus, rheumatoid arthritis, etc.

The prevalence of pyelonephritis is dependent on gender and age. Pyelonephritis is much more common (2-5 times) in women than in men. However, in old age, pyelonephritis prevails in men, which is associated with the development of prostate adenomas in them. In women in 75% of cases, pyelonephritis develops before the age of 40 years, mainly during pregnancy, especially in the second half (in 3-10%, according to M. M. Shekhtman et al., 1980, 1983 and others), less often – in the first period of marriage.

A greater susceptibility to pyelonephritis in women is due to the fact that their urethra is shorter, straighter and. wider than men, and therefore there are more favorable conditions for. penetration of infection into the bladder. In addition, during pregnancy, the pressure of the enlarged uterus disrupts the passage of urine through the ureters, complicates the emptying of the bladder, increases the amount of residual urine, which contributes to the growth and reproduction of pathogenic microflora and its spread in an ascending way. It is also important that during pregnancy there is an expansion and atony of the ureters and pelvis. In the early stages of pregnancy, pronounced functional disorders of the urinary tract develop; the capacity of the pelvis increases 5–10 times, the ureters become significantly longer, the ureters bend, the capacity of the bladder increases, and conditions are created for the occurrence of vesicoureteral reflux. In connection with a decrease in the tone of smooth muscle fibers, the tone of small cups, pelvis and ureters is disturbed. Moreover, the expansion of the ureters is caused not so much by mechanical compression of their pregnant uterus as by hormonal disorders due to changes in the concentration of progesterone, estrogens, and glucocorticoids (M. M. Shekhtman et al., 1980, 1983). It is suggested that in the urine of women, especially pregnant women, there is no hypothetical factor that inhibits the growth of bacteria.

Children develop pyelonephritis mainly under the age of 3 years, and girls are 3-10 times more likely than boys. It is believed that approximately 3% of all girls aged 1-3 years old suffer from pyelonephritis, which is associated with infection of the urethra even during swaddling.

A lower incidence in males in childhood and adulthood is associated, in addition to the structural features of the urinary tract (the urethra in men is longer and narrower than in women, and, in addition, it is curved, which makes it difficult to penetrate and spread the infection), with the secret being detected the prostate gland is a special substance with a wide antibacterial spectrum of action. With adenomas and other diseases of the prostate gland, the release of this substance is markedly reduced, which contributes to the development of pyelonephritis (G. Majdrakov, 1973).

Causes of Pyelonephritis

Since pyelonephritis is a bacterial and inflammatory disease of the kidneys and the pyelocaliceal system, therefore, the main cause of its occurrence is microbes (bacteria), mainly Escherichia coli, a little less often – staphylococcus, vulgar protea, Klebsiella and pseudomonas, and even less often – enterococcus, streptococcus etc. Pyelonephritis can be a consequence of infection of the urinary tract and kidneys or one type of microbes, or mixed microflora. In the urine of patients with acute pyelonephritis, a predominantly pure culture of Escherichia coli is found, and in chronic – mixed microflora. In recent years, there has been a change in the correlation of the etiological role of individual species and strains of microbes with pyelonephritis: staphylococcus and its strains, often resistant to antimicrobials, are becoming the causative agent of this disease. The role of this microbe is especially great at the beginning of the development of acute pyelonephritis, while in the future its growth and reproduction are suppressed by other microbes – Escherichia coli, vulgar protea, etc.

Pathogenesis during Pyelonephritis

Often, especially in the chronic course of the disease, not only the sensitivity of microbes to antibiotics, but also the microflora can change under the influence of treatment: new types of microbes or their associations that are resistant to previously prescribed treatment may arise. In such cases, instead of staphylococcus and Escherichia coli, the growth of a vulgar protea or Pseudomonas aeruginosa resistant to antibiotics is sometimes found.

A significant etiological role in the occurrence of acute pyelonephritis and its transition to chronic is assigned to the so-called L-forms of bacteria and protoplasts. This is a special form of the existence of bacteria, which they acquire under adverse conditions, in particular under the influence of antibiotic therapy on them, completely or partially losing the cell membrane and, as a result, acquiring increased resistance to antimicrobial agents. Under favorable conditions, the formed L-forms of bacteria and protoplasts can restore their cell membrane, turning into the original form of microbes, again capable of reproduction.

There is evidence of the etiological role of viruses in the occurrence of pyelonephritis. However, the question of the possibility of a viral etiology of pyelonephritis has not yet been fully clarified.

Sources of infection leading to pyelonephritis can be carious teeth, chronic tonsillitis, furunculosis, panaritium, mastitis, osteomyelitis, cholecystitis, as well as inflammatory processes in the urinary organs (urethritis, cystitis, etc.) and genital (prostatitis, adnexitis, etc. ) spheres in the pelvic tissue (paraproctitis).

Penetration of infection into the kidney tissue is possible hematogenous (descending), urogenic (ascending) and lymphogenous. The possibility of its spread at the same time hematogenous and urogenic, for example, with the localization of the focus of infection in the lower urinary tract, is not excluded. Often the path of infection in the kidney cannot be established.

With the hematogenous pathway, microbes penetrate through the renal glomeruli into the lumen of the tubules, and then into the interstitial tissue of the kidneys. In the urogenic pathway from the lower parts of the urinary system, they can spread upward along the wall of the ureter (which is recognized by everyone) and along the lumen of the ureter (which is less likely and is considered possible only in the presence of pathological refluxes). Having reached the pelvis, the infection enters the cups, and then into the interstitial tissue of the kidney. Regardless of the path of penetration, the causative agent of infection, once in the interstitial tissue of the kidney, causes the development of an inflammatory process in it.

In the genesis of pyelonephritis, in particular in the mechanism of infection from the pelvis into the kidney tissue, predisposing factors are important, and especially those that lead to a violation of urodynamics. These are abnormalities in the development of the urinary tract (for example, stricture of the ureter or its pronounced atony – ureterocele, doubling of the pelvis and ureters, etc.), the presence of stones, prostate adenoma, and others, as well as pathological refluxes. An important role is played by vesicoureteral reflux, which occurs mainly in children (due to functional insufficiency of the ureteral closure apparatus) and in old age (due to prostate adenoma, sclerosis of the bladder neck, chronic urinary retention). Pathological vesicoureteral reflux is also observed in individuals with the so-called neurogenic bladder.

Violation of urodynamics and urostasis create favorable conditions for the introduction and reproduction of microbes, contribute to their advancement to the pelvis, increase urine pressure in the latter and thus lead to the development of pyelorenal (pyelovenous and pyelolymphatic) refluxes, which contribute to the penetration of the infection into the venous or lymphatic system of the kidneys, and from there to the arterial vessels and glomerular capillaries. Filtered in glomeruli, microbes enter the lumen of the tubules, through the wall of which they penetrate into the interstitial tissue and, multiplying in it, cause the development of the inflammatory process.

The occurrence of pyelonephritis is possible by infection during instrumental research methods (catheterization of the bladder, cystoscopy, retrograde pyelography, etc.), as well as from bedding in a hospital.

In the development of pyelonephritis, some researchers attach great importance to the special “tropism” of certain types (strains) of microbes to renal tissue and their relatively low resistance to microbes. Predispose to the occurrence of pyelonephritis and some common diseases, especially chronic (diabetes, tuberculosis, hypovitaminosis, liver disease, etc.); in women, prolonged use of oral contraceptives that contain estrogens that promote the development of functional (dilatation of the upper urinary tract) and morphological changes in the urinary tract. In the pathogenesis of chronic pyelonephritis, an important role is also given to autoimmune processes, which is confirmed by the detection of a high concentration of anti-renal autoantibodies in the blood.

Symptoms of Pyelonephritis

At different times and by various authors, a number of classifications of pyelonephritis were proposed (N. A. Lopatkin et al., 1974; G. P. Shultsev, 1975 and others). In our country, the most widely used in clinical practice is the classification of pyelonephritis, developed by A. Ya. Pytel (1968, 1977). According to this classification, according to the prevalence of the inflammatory process and its localization, one-sided and two-sided pyelonephritis is distinguished, which in turn can be primary and secondary, and over the course – acute and chronic.

The separation of pyelonephritis into primary and secondary is important not only because they differ in pathogenesis, clinical presentation and course, but also in connection with the peculiarities of their treatment. Primary pyelonephritis includes cases of the disease without previous damage to the kidneys or urinary tract, and secondary cases of the disease, the occurrence of which was preceded by functional or organic changes in the urinary tract, accompanied by impaired passage of urine (calculi, prostate adenoma, developmental anomalies, atony of the ureters or their spasm, reflux, etc.). Secondary pyelonephritis occurs about 3-4 times more often than primary.

According to the route of infection, hematogenous (descending) and urogenic (ascending) pyelonephritis are distinguished. It is believed that primary pyelonephritis initially occurs as interstitial nephritis, followed by the spread of the inflammatory process to the cups and pelvis. This is due to the fact that the infection earlier enters the kidneys (into their interstitial tissue) by the hematogenous route. Secondary pyelonephritis usually begins with the inflammatory process in the pelvis, followed by the spread of infection and the inflammatory process to the interstitial tissue of the kidneys in an ascending way.