Urinary Tract Infection & Interstitial Disease

Question 1

Common routes of infection of UTI

Answer 1

• ascending = most common
  
  • organisms that colonize lower GI/perineal skin are introduced to urethral meatus and ascend into urinary tract
  • most common = E.Coli
• hematogenous (blood-borne) infection
  
  • debilitaed patients/previously damaged kidneys
  • S. aureus, group A streo
  • clinical setting: speticemia, endocarditis

Question 2

Virulence factors that produce UTI

Answer 2

• certain strains of E. coli have P pili which allow attachment to receptors on urothelial cells
  
  • “uropathogenic” ==> agglutinate human RBCs
• blood group P₁ infections > blood group P₂
• endotoxins by E. coli may inhibit ureteral peristalsis

Question 3

Host defense mechanisms against UTI

Answer 3

1. Secretions of urethral glands
2. Mucosal factors
3. Hydrokinetic factors - urine flow
4. Functional “valve” between bladder and ureter that prevents retrograde flow.
5. Urine (poor culture medium).

Question 4

Predisposing factors to UTIs

Answer 4

• females = shorter urethra, more easily irritated + vagina often colonized by bacteria
• instrumentation = catheters, cystoscopy
• decreased urine flow
• calculi = obstruction => perpetuat/spread infection
• vesical-ureteral reflux
• pregnancy
• diabetes = high glucose in urine => good culture medium

Question 5

Causes of decreased urine flow (==> UTI)

Answer 5

1. Urinary tract obstruction
2. Incomplete voiding
3. Infrequent micturition
4. Low flow
5. Bladder/ureteral diverticula
6. Neurologic diseases affecting bladder control

Question 6

Clinical manifestations of UTIs

Answer 6

• covert bacteriuria
  
  • F>>M
  • some may have chronic pyelonephritis
  • scarring occurs in young children
• symptomatic UTI

Question 7

Symptoms of UTI @ urethra and vesical-urethral valve

Answer 7

• dysuria
• difficulty voiding
• incomplete emptying
• incontinence

Question 8

Symptoms of UTI @ bladder (cystitis)

Answer 8

• frequency
• suprapubic pain
• • sx of urethra UTI

Question 9

Symptoms of UTI @ ureters and kidneys (acute pyelonephritis)

Answer 9

• flank pain + tenderness
• abdominal pain
• fever, chills
• oliguria
• • sx of cystitis + sx of urethral infection

Question 10

Lab features of UTI

Answer 10

1. Urinalysis: Many WBC’s, WBC casts (pyelonephritis), RBC’s (variable).
2. urine culture: usually > 100,000 bacteria/ml; always > 10,000 bacterial/ml

Question 11

Major complications of UTIs

Answer 11

1. Acute pyelonephritis = suppurative inflammation of kidney and renal pelvis from bacterial infection
2. perinephric abscess = usually w/acute pyelonephritis
3. renal scarring
4. recorrence
5. stones = esp. w/proteus infection

Question 12

Characteristics of acute pyelonephritis

Answer 12

1. Patchy, wedge-shaped regions of suppuration with microabscesses.
2. Tubules filled with aggregates of PMNs
3. Tubular destruction
4. Interstitium – edema, PMNs, lymphs and plasma cells (may predominate in areas away from abscesses or during resolution).
5. Glomeruli preserved until late in course

Question 13

Major causes of chronic pyelonephritis

Answer 13

• when combined w/chronic or recurrent infections ==> renal scarring + progressive renal impairment
• urinary tract obstruction
• vesical-ureteral reflux (VUR)

Question 14

Pathogenesis of chronic pyelonephritis caused by urinary tract obstruction

Answer 14

• obstruction predisposes to infection
• obstruction ==> difficult to eradicate; more recurrence
• obstruction + infection ==> structural kidney damage
  
  • pressure-induced ischemia + tubular atrophy
  • tissue injury due to bacteria/inflammation

Question 15

Causes of obstruction ==> chronic pyelonephritis

Answer 15

1. Intrinsic (intraluminal) masses of the urinary tract:

• exophytic tumors
• calculi
• blood clots

1. Inflammation, stricture of urethra or ureters
2. Urethral valves
3. Extrinsic compression:

• tumors (esp. pelvis, retroperitoneal)
• retroperitoneal fibrosis
• hemorrhage (trauma)
• iatrogenic (surgical ligation, adhesions)

1. Functional:

• neurological disease
• diabetes mellitus

1. Idiopathic

Question 16

Consequences of chronic obstructive pyelonephritis

Answer 16

• structural changes
  
  • hydronephrosis
  • atrophy + flattening of renal papillae/medulla
  • fibrosis/atrophy of renal cortex
  • microscopic: tubular atrophy + fibrosis w/patchy inflitrate of lymphs + edema/PMNs (if acute infection)
• functional changes
  
  • decreased GFR
  • HTN

Question 17

Common causes of VUR

Answer 17

• normal: oblique course of ureter effectively forms “valve”
• if ureter enters perpindicularly ==> valve is lost ==> urine reflux into ureter
• most common: abnormality in infancy and resolves through childhood
  
  • familial

Question 18

Characteristics of reflux nephropathy

Answer 18

• = VUR + chronic/recurrent infection
• usually associated w/HTN
• organisms can gain access to renal parenchyma via reflux
• ==> scars @ calcyces
  
  • thinning of cortex and medulla
• extensive scarring at poles of kidney
• small percentage of pts develop focal segmental glomerulosclerosis