Canine Cystitis Study Guide

Overview and Clinical Importance

Bacterial cystitis is inflammation of the urinary bladder caused by bacterial infection. It represents one of the most common infectious diseases in dogs, affecting approximately 14% of dogs at some point during their lifetime. Unlike cats, where most lower urinary tract disease is idiopathic and sterile, bacterial infection is the predominant cause of cystitis in dogs. This distinction is critical for the NAVLE, as it influences diagnostic and therapeutic approaches.

Cystitis typically arises from bacteria ascending from the perineum through the urethra to the bladder. Female dogs are at significantly higher risk due to their shorter, wider urethra compared to males. The urinary tract possesses multiple defense mechanisms against infection, including antimicrobial peptides in urine, high urine osmolality, the physical barrier of the urothelium, and normal voiding patterns that flush bacteria. Bacterial cystitis occurs when these host defenses are compromised.

Classification of Bacterial Urinary Tract Disease

Understanding the classification of bacterial urinary tract disease is essential for appropriate diagnosis and management. The 2019 ISCAID guidelines provide standardized definitions that have replaced older terminology such as "simple" and "complicated" UTI.

Etiology and Pathogenesis

Common Bacterial Pathogens

Most cases of bacterial cystitis in dogs are caused by a single organism. Escherichia coli is the most commonly isolated pathogen, accounting for approximately 50-70% of all canine UTIs. Understanding the typical pathogens guides empirical therapy selection.

Host Defense Mechanisms

The urinary tract possesses multiple defense mechanisms that must be breached for infection to occur:

• Antimicrobial peptides: Present in urine; prevent bacterial adherence and proliferation on the urothelium
• High urine osmolality: Concentrated urine creates hostile environment for bacterial growth
• Urothelial barrier: Glycosaminoglycan layer and tight junctions prevent bacterial attachment
• Normal voiding: Regular, complete bladder emptying flushes bacteria before colonization
• Immune response: Local and systemic immune mechanisms eliminate invading pathogens

Clinical Presentation

Classic Clinical Signs

The classic triad of lower urinary tract disease includes pollakiuria, stranguria/dysuria, and hematuria. However, these signs are NOT pathognomonic for bacterial infection and can occur with any cause of bladder inflammation.

Physical Examination Findings

Physical examination findings are often unremarkable in uncomplicated bacterial cystitis. Important findings to assess include:

• Bladder palpation: May reveal thickened bladder wall; bladder often small due to frequent voiding; pain on palpation
• Vulvar examination (females): Assess for recessed vulva, perivulvar dermatitis, or vaginal discharge
• Rectal examination (intact males): Evaluate prostate for size, symmetry, and pain; prostatic involvement = complicated UTI
• Systemic signs: Fever, lethargy, anorexia suggest pyelonephritis or sepsis; require more aggressive workup

Diagnostic Approach

Urinalysis

Complete urinalysis is the cornerstone of UTI diagnosis. It should include urine specific gravity, dipstick analysis, and microscopic sediment examination. Cystocentesis is the preferred collection method as it prevents contamination and allows meaningful interpretation of culture results.

Exam Focus: The leukocyte esterase and nitrite pads on urine dipsticks are INACCURATE in dogs and cats! Never use these for UTI diagnosis in veterinary patients. Only pyuria on sediment examination and urine culture are reliable for diagnosis.

Urine Culture and Sensitivity

Quantitative aerobic urine culture is the gold standard for diagnosis of bacterial cystitis. It confirms infection, identifies the pathogen, and guides antimicrobial selection through sensitivity testing.

Diagnostic Imaging

Imaging is not required for sporadic bacterial cystitis but becomes essential for recurrent infections to identify underlying causes.

Ultrasonography

Ultrasonography provides excellent evaluation of bladder wall thickness, masses, and calculi. Key findings in cystitis include:

• Wall thickening: Normal canine bladder wall is less than 3 mm with adequate distension; thickening suggests chronic inflammation
• Mucosal irregularity: Loss of smooth inner surface; most pronounced cranioventrally in chronic cystitis
• Echogenic debris: Cellular debris or blood clots in bladder lumen
• Calculi: Hyperechoic structures with acoustic shadowing (regardless of composition)

Radiography

Radiography is useful for detecting radiopaque uroliths and identifying complications such as emphysematous cystitis. Contrast studies (cystography) may be needed for radiolucent stones, masses, or anatomical abnormalities not visible on survey radiographs.

Special Forms of Cystitis

Emphysematous Cystitis

Emphysematous cystitis is characterized by gas accumulation within the bladder wall and/or lumen due to infection with glucose-fermenting bacteria. It is most commonly associated with diabetes mellitus due to the high concentration of fermentable substrate (glucose) in urine. E. coli is the most common causative organism, though Proteus, Klebsiella, and Clostridium species have also been reported.

Imaging findings: On radiography, mottled gas opacities appear within the bladder wall (intramural gas) or free gas within the lumen. On ultrasonography, hyperechoic foci with reverberation artifacts are seen. Ultrasound is more sensitive for detecting early or small amounts of gas.

Polypoid Cystitis

Polypoid cystitis is characterized by benign epithelial proliferations (polyps) projecting into the bladder lumen, typically located cranioventrally. It results from chronic inflammation, often associated with recurrent UTIs, urolithiasis, or chronic catheterization. The condition must be differentiated from transitional cell carcinoma (TCC) through histopathology.

Key differentiating features from TCC:

• Location: Polypoid cystitis is cranioventral; TCC has predilection for trigone
• Appearance: Polyps are often pedunculated; TCC has broad-based attachment
• Definitive diagnosis: ALWAYS requires histopathology via cystoscopy or suction biopsy

Treatment Guidelines (ISCAID 2019)

Sporadic Bacterial Cystitis

The 2019 ISCAID guidelines recommend short-course antimicrobial therapy (3-5 days) for sporadic bacterial cystitis. This represents a significant change from previous recommendations of 10-14 days and is based on evidence that short courses are equally effective while reducing antimicrobial exposure.

Recurrent and Complicated Infections

Recurrent and complicated infections require a different approach with extended treatment duration and thorough investigation for underlying causes.

Supportive Therapy

NSAIDs can provide analgesia while awaiting culture results or as adjunctive therapy. Always verify renal function before use. Increased water intake to promote urinary dilution and frequent voiding can help flush bacteria from the urinary tract.

Predisposing Factors and Comorbidities

Identification of underlying conditions is essential for managing recurrent UTIs. These comorbidities must be addressed for successful treatment.

Monitoring and Follow-up

Sporadic Cystitis

For sporadic bacterial cystitis, routine post-treatment urinalysis or culture is NOT indicated if clinical signs resolve. Owners should monitor for resolution of clinical signs, which typically occurs within 48-72 hours. Recheck only if signs persist or recur.

Recurrent/Complicated Infections

For complicated infections, perform urine culture:

• 5-7 days after starting treatment (to confirm appropriate therapy)
• 7-14 days after completing treatment (to confirm cure)
• 1-3 months post-treatment for monitoring in high-risk patients