Cystitis

Cystitis is the inflammation of the urinary bladder, commonly of infectious origin, but can also be sterile or non-infectious. It is a frequent diagnosis in small animal practice, particularly in female dogs and cats. The condition can be acute or chronic, and may be complicated by urolithiasis, anatomical abnormalities, or systemic diseases. In severe cases, cystitis can ascend to the upper urinary tract, leading to pyelonephritis and potential renal damage. The clinical presentation varies from asymptomatic bacteriuria to severe dysuria, hematuria, and pollakiuria. Proper diagnosis and management are essential to prevent recurrence and complications.

The most common causative agents are bacteria, with Escherichia coli being the predominant pathogen (50-70% of cases), followed by Staphylococcus spp., Proteus spp., Klebsiella spp., Enterococcus spp., and Pseudomonas spp. In cats, bacterial cystitis is less common, with sterile cystitis (feline idiopathic cystitis) being more prevalent. Other infectious causes include fungal (Candida, Aspergillus), viral (rare), and parasitic (Capillaria plica, Dioctophyma renale) agents. Non-infectious etiologies include urolithiasis (struvite, calcium oxalate, urate, cystine), neoplasia (transitional cell carcinoma), trauma, radiation, and drug-induced (e.g., cyclophosphamide). In some cases, cystitis may be secondary to anatomical abnormalities such as ectopic ureters, urachal remnants, or vaginal strictures.

Cystitis is one of the most common urinary tract disorders in dogs and cats. In dogs, the prevalence is higher in females due to a shorter and wider urethra, with a peak incidence in middle-aged to older animals. Certain breeds, such as the Dalmatian (urate stones), Miniature Schnauzer (calcium oxalate stones), and Shih Tzu (struvite stones), have a genetic predisposition to urolithiasis-associated cystitis. In cats, feline idiopathic cystitis (FIC) is the most common cause of lower urinary tract signs, accounting for 50-60% of cases, and is more frequent in young to middle-aged cats, indoor cats, and those under stress. Bacterial cystitis is less common in cats, with a higher incidence in older cats and those with concurrent diseases such as chronic kidney disease or diabetes mellitus.

The pathogenesis of bacterial cystitis begins with the adherence of uropathogenic bacteria to the urothelium via fimbriae and adhesins. This triggers an inflammatory response, with the release of cytokines and chemokines, leading to vasodilation, increased vascular permeability, and recruitment of neutrophils and macrophages. The inflammatory infiltrate causes mucosal edema, hyperemia, and desquamation of urothelial cells, resulting in hematuria and dysuria. In chronic cases, fibrosis and thickening of the bladder wall may occur. For urolithiasis-associated cystitis, the presence of crystals or stones causes mechanical irritation and mucosal damage, predisposing to secondary bacterial infection. In feline idiopathic cystitis, the pathophysiology is complex and involves a defective bladder mucosal barrier, neurogenic inflammation, and stress-induced activation of the hypothalamic-pituitary-adrenal axis, leading to mast cell degranulation and release of substance P and other neuropeptides.

Intrinsic risk factors include female sex, anatomical abnormalities (e.g., recessed vulva, vaginal stricture), urolithiasis, neoplasia, chronic kidney disease, diabetes mellitus, hyperadrenocorticism, and immunosuppression. Extrinsic factors include poor hygiene, infrequent voiding, stress (especially in cats), dietary factors (e.g., high magnesium and phosphorus for struvite stones), and the use of urinary catheters. In cats, environmental stressors such as multi-cat households, changes in routine, and litter box issues are significant triggers for FIC.

Clinical signs of cystitis include pollakiuria, stranguria, dysuria, hematuria (often terminal), and inappropriate urination (especially in cats). On physical examination, the bladder may be small and painful on palpation. In severe cases, systemic signs such as fever, lethargy, and anorexia may be present, especially if pyelonephritis or prostatitis is concurrent. Chronic cases may present with a thickened bladder wall and signs of lower urinary tract obstruction, particularly in male cats with urethral plugs.

Differential diagnoses include urolithiasis, urinary tract neoplasia (e.g., transitional cell carcinoma), feline idiopathic cystitis, pyelonephritis, prostatitis, urethritis, vaginitis, and neurogenic bladder dysfunction. Key distinguishing features: urolithiasis is often identified on imaging (radiographs or ultrasound) and urinalysis (crystals); neoplasia is more common in older dogs and may present with a palpable mass, and cytology/histopathology is diagnostic; pyelonephritis is associated with fever, lumbar pain, and renal pelvic dilation on ultrasound; prostatitis is more common in intact male dogs and may present with prostatomegaly and seminal fluid changes; urethritis may be associated with urethral discharge; vaginitis is characterized by vaginal discharge and inflammation on vaginoscopy; neurogenic bladder dysfunction is associated with neurological deficits and a large, easily expressible bladder.

The diagnostic approach begins with a thorough history and physical examination. Urinalysis is the cornerstone, including urine specific gravity, dipstick, and sediment examination. A urine culture and sensitivity should be performed in all cases of suspected bacterial cystitis, especially in recurrent or complicated cases. Imaging is recommended for recurrent cystitis, suspected urolithiasis, or anatomical abnormalities. Abdominal radiographs can detect radiopaque uroliths, while ultrasonography is more sensitive for bladder wall thickening, masses, and radiolucent stones. Contrast studies (e.g., cystography) may be needed for anatomical defects. Cystoscopy is the gold standard for evaluating the bladder mucosa and obtaining biopsy samples. In cases of suspected neoplasia, cytology of urine sediment or fine-needle aspiration of a mass may be performed.

Complete blood count may show neutrophilia with a left shift in cases of severe bacterial infection. Serum biochemistry may reveal elevated renal parameters (BUN, creatinine) if pyelonephritis is present. Urinalysis typically shows hematuria, proteinuria, and pyuria. The urine sediment may contain bacteria, crystals, and epithelial cells. Urine culture is essential for identifying the causative organism and determining antimicrobial susceptibility. In cases of recurrent cystitis, additional tests such as urine protein-to-creatinine ratio, blood pressure measurement, and endocrine testing (e.g., cortisol, thyroid) may be indicated.

Abdominal radiography can reveal radiopaque uroliths (struvite, calcium oxalate) and may show a distended bladder. Ultrasonography is more sensitive for detecting bladder wall thickening, polyps, masses, and radiolucent stones (urate, cystine). It can also assess the kidneys and ureters for signs of pyelonephritis. Contrast cystography can outline the bladder lumen and detect filling defects or diverticula. Computed tomography (CT) is useful for evaluating the entire urinary tract, especially in cases of suspected neoplasia or complex urolithiasis. Cystoscopy allows direct visualization of the bladder mucosa and can be used for biopsy and stone removal.

Cytological examination of urine sediment may show inflammatory cells (neutrophils, lymphocytes, macrophages), erythrocytes, and bacteria. In cases of neoplasia, transitional cell carcinoma cells may be seen. Histopathological examination of bladder biopsy samples is the gold standard for diagnosing chronic cystitis, neoplasia, and other infiltrative diseases. Findings may include mucosal ulceration, inflammatory infiltrate, fibrosis, and in cases of neoplasia, malignant cell proliferation.

Treatment depends on the underlying cause. For bacterial cystitis, antimicrobial therapy should be based on culture and sensitivity results. Empirical therapy may be initiated with amoxicillin-clavulanate (13.75 mg/kg PO q12h) or trimethoprim-sulfamethoxazole (15 mg/kg PO q12h) while awaiting culture results. The duration of therapy is typically 7-14 days, but may be extended to 4-6 weeks for complicated or recurrent infections. For urolithiasis, dietary management (e.g., therapeutic diets to dissolve struvite stones) or surgical removal may be necessary. For feline idiopathic cystitis, stress reduction, environmental enrichment, and increased water intake are key. Analgesics such as buprenorphine (0.01-0.02 mg/kg PO/IV q8-12h) may be used for pain. In severe cases, anti-inflammatory doses of corticosteroids (e.g., prednisolone 0.5-1 mg/kg PO q12h) may be considered, but their use is controversial. For neoplasia, surgical excision, chemotherapy, or radiation therapy may be indicated.

The prognosis for uncomplicated bacterial cystitis is excellent with appropriate antimicrobial therapy. Recurrence is common, especially in animals with underlying predisposing factors. For urolithiasis, the prognosis is good if the underlying cause is managed. Feline idiopathic cystitis has a guarded prognosis, with a high recurrence rate, but many cats respond to environmental and dietary modifications. The prognosis for neoplasia is poor, with a median survival time of 6-12 months for transitional cell carcinoma.

Recheck urinalysis and urine culture 7-14 days after completion of antimicrobial therapy to ensure resolution of infection. For recurrent cystitis, periodic urine cultures and imaging may be recommended. For urolithiasis, follow-up imaging is needed to monitor stone dissolution or recurrence. For feline idiopathic cystitis, regular monitoring of clinical signs and adjustment of environmental management is essential.

Pearls: Always perform a urine culture in recurrent or complicated cystitis. In cats, consider FIC as a primary differential, and avoid unnecessary antibiotics. Use appropriate antimicrobial dosages and durations to prevent resistance. Pitfalls: Do not rely solely on urinalysis for diagnosis; culture is essential. Avoid using corticosteroids in bacterial cystitis. Do not overlook underlying causes such as urolithiasis or neoplasia.

Antimicrobials: Amoxicillin-clavulanate (13.75 mg/kg PO q12h), Cefpodoxime (5-10 mg/kg PO q24h), Enrofloxacin (5-10 mg/kg PO q24h, but avoid in young animals due to cartilage damage), Doxycycline (5-10 mg/kg PO q12h). Analgesics: Buprenorphine (0.01-0.02 mg/kg PO/IV q8-12h), Meloxicam (0.1 mg/kg PO q24h for dogs, but caution in cats). Anti-inflammatories: Prednisolone (0.5-1 mg/kg PO q12h for FIC). Urinary acidifiers/alkalinizers: Ammonium chloride (100 mg/kg PO q12h) for struvite dissolution, but not recommended for calcium oxalate. For FIC, amitriptyline (5-10 mg/cat PO q24h) or fluoxetine (0.5-1 mg/kg PO q24h) may be used for chronic management.

According to the International Society for Companion Animal Infectious Diseases (ISCAID) guidelines, antimicrobial therapy is recommended only for bacterial cystitis confirmed by culture. For uncomplicated cases, a 7-day course is sufficient. For recurrent cystitis, a 14-day course is recommended. Studies have shown that E. coli is the most common pathogen, and resistance to amoxicillin is increasing. In feline idiopathic cystitis, a multimodal approach including environmental enrichment and stress reduction is more effective than pharmacotherapy alone. The use of glycosaminoglycan supplementation (e.g., Cosequin) has shown some benefit in reducing recurrence.