Pyelonephritis - Information Overview

Pyelonephritis is a non-specific infectious and inflammatory disease of the kidney.

The term is commonly used to describe an infectious process involving the kidneys and adjacent structures. The infection may be ascending and involve both the renal pelvis and the kidney, or metastatic and limited to the renal parenchyma. When the infection spreads to the underlying tissues, a perinephric abscess or paranephritis is formed.

ICD-10 codes

• N10. Acute tubulointerstitial nephritis.
• N11. Chronic tubulointerstitial nephritis.
• N13.6. Pyonephrosis.
• N15.1. Abscess of the kidney and perirenal tissue.

Below are listed the nosological forms according to ICD-10 that are not associated with infection:

• N11.0. Non-obstructive chronic pyelonephritis associated with reflux.
• N11.1. Chronic obstructive pyelonephritis.

Pyelonephritis includes one or more of the following conditions:

• acute or chronically active infection;
• residual lesions and scars from past infection;
• local immune inflammatory response to infection;
• a combination of all these processes.

Epidemiology of pyelonephritis

Pyelonephritis is a common disease. However, there are no reliable population-based epidemiological studies describing the incidence of pyelonephritis. Even for groups such as patients with diabetes mellitus, who have a high risk of developing the disease with its most severe course, there are no statistically reliable data.

In children, pyelonephritis ranks second after respiratory diseases. In young and middle-aged women and girls, acute uncomplicated pyelonephritis occurs 5 times more often than in men and boys.

Despite the high incidence of the disease in women, the course of uncomplicated non-obstructive pyelonephritis is favorable. Pyelonephritis is detected in 8-20% of autopsies, equally in men and women. However, there is no evidence that it had an infectious origin.

The higher incidence of ascending urinary tract infections and pyelonephritis in girls and women is due to anatomical and physiological features:

• short and wide urethra;
• proximity to natural reservoirs of infection (vestibule of the vagina, rectum);
• frequent concomitant inflammatory gynecological diseases;
• frequently occurring right-sided nephroptosis, with impaired urodynamics of the upper urinary tract and blood supply to the kidney;
• violation of urodynamics of the upper urinary tract, compression of the lower third of the ureters by the enlarged uterus during pregnancy;
• atrophy of the urinary tract mucosa in postmenopause.

During pregnancy, acute pyelonephritis is observed in 3-11% of women.

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What causes pyelonephritis?

Infectious pyelonephritis is primarily caused by gram-negative or gram-positive bacteria, usually those that cause urinary tract infection (bacterial pyelonephritis). Other possible pathogens include Mycobacterium tuberculosis (renal tuberculosis), yeast (candidal pyelonephritis), other fungi, and viruses. Patients with acute uncomplicated pyelonephritis rarely develop hypertension or recurrent kidney injury. Patients with complicated infection are more likely to develop sepsis and severe kidney injury. Patients with obstruction and neurogenic urinary tract abnormalities, diabetes mellitus, polycystic kidney disease, stones, and urinary catheters are also at high risk for severe kidney infection. Infection caused by urease-producing microorganisms leads to the formation of infectious (struvite) stones.

Patients with diabetes mellitus have an increased risk of developing destructive (purulent) forms of the disease: apostematous and emphysematous pyelonephritis, carbuncle and renal abscess, papillary necrosis. Patients with long-standing, complicated infection may develop a rare condition known as xanthogranulomatous pyelonephritis. In the past, pyelonephritis was considered one of the common causes of arterial hypertension and severe kidney disease. Currently, it is known that reflux nephropathy causes significantly more kidney damage, which was previously attributed to chronic pyelonephritis. Many diseases can imitate bacterial pyelonephritis, such as analgesic nephropathy, interstitial nephritis, and vascular diseases of the kidneys.

What causes pyelonephritis?

Classification of pyelonephritis

There are many classifications of urinary tract and urogenital infections. At the same time, the classifications of acute pyelonephritis adopted in Russia distinguish only the stages of acute infectious and inflammatory process in the interstitium and in the renal parenchyma (serous, purulent), but not topical forms of damage to the kidney itself or the renal pelvis, and damage to the pelvis is not reflected in these classifications at all, which contradicts the very concept of "pyelonephritis".

Classification of pyelonephritis according to S. Kunin (1997):

• acute complicated bacterial pyelonephritis (focal or diffuse);
• lobar nephronia;
• chronic complicated bacterial pyelonephritis;
• pyonephrosis;
• emphysematous pyelonephritis:
• papillary necrosis of the kidney;
• xanthogranulomatous pyelonephritis;
• malakoplakia;
• pyelonephritis Lenta (infection localized in the upper urinary tract);
• renal abscess and perinephric abscess;
• infection superimposed on polycystic kidney disease;
• kidney infection caused by less common microorganisms;
• tuberculosis of the kidneys and other mycobacterial infections;
• fungal infections;
• viral infections.

Classification of urinary tract and genitourinary infections according to the European Association of Urology Guidelines (2006):

• uncomplicated lower urinary tract infections (cystitis);
• uncomplicated pyelonephritis;
• complicated urinary tract infection with and without pyelonephritis;
• urosepsis;
• urethritis;
• special forms: prostatitis, epididymitis and orchitis.

Depending on the course, there are uncomplicated (primary) and complicated (secondary, recurrent) urinary tract infections. The term "chronic" for urinary tract infections is usually not used, since in most cases it incorrectly reflects the course of the disease. As a rule, chronic pyelonephritis develops after a bacterial infection that occurs against the background of anatomical abnormalities of the urinary tract (obstruction, vesicoureteral reflux), infected stones. It is believed that up to 60% of human infections are associated with biofilm infection. Biofilm infection is understood as the adhesion of microorganisms to the surface of mucous membranes, stones or biomaterials (catheters, drains, artificial prostheses, sphincters, meshes, etc.). Microorganisms then begin to live and multiply on them, periodically developing aggression against the host - the macroorganism.

Uncomplicated infections are more common in young women, while there is no such distinction for complicated (secondary) infections. Complications of infections occur against the background of functional disorders or anatomical abnormalities of the urinary tract, after catheterization of the bladder or renal pelvis and interventions on the urinary tract, against the background of severe concomitant diseases: diabetes mellitus, urolithiasis, chronic renal failure, etc. In 30% of cases, secondary or complicated infections are of hospital-acquired (hospital, nosocomial) origin. Finally, secondary infections are less treatable, often recur, are associated with a higher risk of damage to the renal parenchyma, the development of a kidney abscess and urosepsis, and among the pathogens, strains of microorganisms resistant to antibacterial drugs are more often encountered.

Recurrent urinary tract infections include recurrent (true relapses), repeated (reinfections), and resistant or asymptomatic bacteriuria.

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