Urolithiasis in Small Animals PDF

Urolithiasis Dr Glynn Woods BVMS MSc Dip.ECVIM-CA MRCVS RCVS and EBVS recognized specialist in small animal internal medicine Senior Lecturer, University of Edinburgh [email protected] Learning objective • Discuss uroliths formation and possible underlying causes • Be able to localize urolith based...

Urolithiasis Dr Glynn Woods BVMS MSc Dip.ECVIM-CA MRCVS RCVS and EBVS recognized specialist in small animal internal medicine Senior Lecturer, University of Edinburgh [email protected] Learning objective • Discuss uroliths formation and possible underlying causes • Be able to localize urolith based on clinical signs and identify signs of obstruction • Know the diagnostic tests necessary for the work-up of patients with urolithiasis including investigation of possible causes and complications • Be able to guesstimate the type of urolith based on signalment and diagnostic findings of the patient • Know indications for medical dissolution vs urolith retrieval in a patient • Be able to generate a treatment plan for a patient with a given type of urolithiasis Definition - Pathophysiology Urolithiasis is NOT a specific disease • Systemic disorders • Hypercalcemia • Hyperadrenocorticism • Defect in purine metabolism - hyperuricosuria • Urinary tract disorder • • • • Renal tubular disease Defects in local host defenses against microbes Foreign body in urinary tract Catheters • Nidus • Bacteria • Epithelial cells • Foreign material • Nidus • Nucleus • Aggregation of crystals • Can occur without a nidus • Nidus • Nucleus • Stone • Formation of more crystal aggregates into a lattice • Continued growth • Nidus • Nucleus • Stone • Formation of more crystal aggregates into a lattice • Continued growth • Nidus • Nucleus • Stone • Outer surface crystals • Compound uroliths • May be different type OVERSATURATED Spontaneous nucleation Maximal crystal growth and aggregation Crystals will not dissolve SUPERSATURATED Minimal crystal growth and aggregation Requires nidus for nucleation Crystals will not dissolve UNDERSATURATED No crystal growth or aggregation No nidus formation Crystals can dissolve Factors that influence the growth of a urolith • Urine pH • Urine concentration • Frequency of voiding • Drinking habits and diet • Presence or absence of promoters/inhibitors of crystallization • Infection > struvite urolithiasis • In turn things that contribute to infection • Citrate + Magnesium > calcium urolithiasis Urolith consequences – clinical importance? Signalment • One of the biggest example of pattern recognition in vet medicine • Breed, sex, age can provide clues to urolith composition Clinical signs and physical exam depend… 1. Location of urolith 2. Duration of their presence 3. Underlying / concurrent disease Hypercalcaemic dog Portal systemic shunt dog Urinary tract infection Nephroliths • Often incidental • Investigating CKD! • Investigating recurrent UTI • Haematuria • Renal pain • Paraspinal pain • Obstruction • Vomiting • Azotaemia • Pyrexia General management: Nephrolithiasis • Shock wave therapy • • • • Limited centres Struvite/Calcium oxalate J Cysteine L Only dogs • Endoscopic nephrolithotomy • Surgical intervention • SUBS/Stent if obstruction • Medical dissolution Ureteroliths • Can be asymptomatic / incidental • Post-renal azotaemia • AKI, Hyperkalaemia (esp bilateral) • “Big kidney little kidney” • Blockage (i.e hydroureter) • Obstructive nephropathy • Calcium oxalate > Struvite (unless UTI) • Haematuria General management: Ureteroliths • Shockwave therapy • Surgical intervention • Medical expulsive therapy SUB Ureteric stenting Cystoliths • Can be asymptomatic • Dysuria • Abdominal pain • Haematuria General management: Cystoliths • Dissolution • Bathe in urine • Hydropulsion • Not male cats • Size of urethra – contrast ($) • Size of urethra – 8fr – 2.4mm • Cystotomy • Percutaneous cystolithotomy (PCCL) • Laser lithotripsy Urethroliths • Obstruction • Post-renal azotaemia • Uroabdomen • ”Constipation” or “Incontinence” General management: Urethroliths • Catheter placement • Retrograde hydropulsion • Urethrotomy / Urethrostomy • Laser lithotripsy Diagnosis Diagnostics • Urine analysis • pH • Specific gravity • Sediment • Unstained > crystals • Stained > bacteria • Urine culture and sensitivity • Serum biochemistry • Liver function • Azotaemia • Ca2+ Diagnostics • Ultrasound • All forms of urolithiasis • Obstruction • Free fluid • The perineum! • Radiographs • Density • Quantify • Measure I can’t C U x Treatment Uroliths general treatment considerations • Increase water intake (wet food) + Increase urination frequency • Do we actually have to treat the urolith? • If we have to treat the urolith… • Always consider medical vs surgical vs minimally invasive • Limitations of medical dissolution + of surgical removal • Clients need to be on board – recurrence rates high! Struvite urolithiasis AKA Magnesium ammonium phosphate uroliths Struvite (Magnesium ammonium phosphate) • Young, Females > Males • Neutral to alkaline pH • Urease producers • Staphylococcus, Proteus/Pseudomonas, Corynebacterium, Ureaplasma • Radio-opaque, Circular, Multiple, Varying size Diagnosis • Sediment exam • Culture and sensitivity Treatment • Treat the underlying UTI (Dogs) • Throughout entire dissolution period (+/- evidence) • Feed a wet dissolution diet • Acidic pH • Not complete diet • D- Methione > acidifier • Restricted in: • Mg2+, NH3, PO4 • Huge improvement in 4-8 weeks and most dissolved by 12w Prevention • Exclude causes of recurrent/resistant infections • Maintenance diet • Hill’s c/d multicare • Hill’s w/d • Others as per manufacturer • Dilute urine • Wet diet • Additional water • SG/crystal checks Calcium oxalate urolithiasis Hypercalcemia (5% dogs – 35% cats) Calcium Oxalate • Older, Males > Females • Ionised Hypercalcaemia • Nephrolithiasis (Upper > Lower) • Radiodense, Jagged edges, 1 or (X) Diagnosis • Urine analysis • • • • pH Haematuria Monohydrate - Ethylene glycol Dihydrate - “Usual” form • Haematology • Lymphoma (Paraneoplastic iCa) • Biochemistry • Ionised calcium • Phosphate • Triglycerides (Schnazuers) Monohydrate Dihydrate Diagnosis Treatment • Not amenable to dissolution • Treat hypercalcaemia if present • Surgical removal / Diversion (SUB) • Benign neglect • Owner monitoring signs Prevention • Dilution • Potassium citrate • If pH < 6.5 consistently • Thiazide diuretics • Unless serum hypercalcaemia • Diet (Magnesium / Citrate) • Hill’s c/d multicare • Hill’s u/d Urate urolithiasis Urate stones • Young, Males • 97% of Dalmations (Gene = SLC2A9) • cPSS/Liver • Multiple, Small, Yellow-green, Radiolucent NOT SOLUBLE PURINES HYPOXANTHINE XANTHINE XANTHINE OXIDASE SOLUBLE URIC ACID ALLANTOIN URICASE SLC2A9 Diagnosis • Haematology • Shunt suggestive • Co-morbidities • Serum biochemistry • Liver function tests • Bile acid stimulation testing • Ammonia • Urine analysis • pH – Acidic • Sediment exam • Concurrent UTI Treatment • Dilution • Potassium citrate • if pH < 6.5 • Diet NOT SOLUBLE • Low purine • Purina HA / Hils UD • Correct underlying disease • Hepatopathy • Shunt ligation HYPOXANTHINE XANTHINE SOLUBLE URIC ACID ALLANTOIN • Allopurinol • Limited effect in cPSS • Diet necessary with allopurinol • Risk of Xanthine urolithiasis XANTHINE OXIDASE URICASE Cystine • Middle age, Males • Mutation affecting tubules • SLC3A1 • SLC7A9 • Cystine wasting • Round and smooth, Light brown/yellow , Usually multiple , Faintly radioopaque Diagnosis • Urine analysis • Sediment • Genetic testing • • • • Mastiff Bulldog Newfoundland French Bulldog • Urine cystine levels Treatment • Wet diet • Lower animal protein content • Alkalinising (pH of 7.5) • Hill’s u/d • Tiopronin (“Thiola” or 2-MPG) • Binds cystine, Forming disulphide linked bonds > Increases solubility • Penicillamine • GI side effects • Can be effective • Castration • Androgen responsive form • Deerhound, Mastiff, Bulldog • May not resolve issue General monitoring • Urine analysis • • • • Every 2 – 4 weeks 3 – 6 months Specific gravity pH • Imaging • Ultrasound or radiographs • Every 6 – 12 months • Allow intervention early - VHydro Type of urolith pH during formation Target urinary pH Specific treatment considerations Struvite Alkaline Acidic • Treat UTI • Medical dissolution Calcium oxalate Acidic Alkaline • • • • Is Tx necessary? Thiazides safe? Can’t dissolve Minimally invasive or surgical removal Ammonium urate Acidic Alkaline • • • • • Genetic cause Liver dx or PSS Allopurinol Low purine diet Xanthine risk Cystine Acidic Alkaline • • • • Genetic Castrate Thiola Penacillamine Take home message • Uroliths are concretions of a crystal aggregate that can form in any part of the urinary tract and in association with various factors/underlying causes • Diagnosis involves recognition of typical clinical signs associated with urolith localization • Diagnostic work-up include bloodwork, urinalysis, urine culture, imaging test and ideally, urolith composition analysis • Signalment, urine composition, presence of absence of a UTI, blood work findings and radiographic appearance of the stone allow approximation of urolith. • Treatment involves medical dissolution and mechanical retrieval • Except for UTI induced struvite, life long prevention to avoid recurrence