Urolithiasis

Uroliths Aggregations of sedimented urinary solutes (minerals, proteins) Central nidus (usually protein), surrounded by laminar ”stone” and surface crystals

Causes obstructions usually in males’ ureter At the site of obstruction, there is local pressure necrosis, ulceration of the mucosa and acute hemorrhagic urethritis Often in cats, dogs and ruminants Seldom in horses and pigs

Causes Urinary pH Reduced water intake causes crystallization Feeding; for exaple low vitamin A, high phosphorus in ruminants, magnesium in cats causes mucosal damage which produces nidi for the stones Inflammation; leukocytes, fibrin, epithelial cells also serve as a nidus Inborn error of metabolism

Struvite stones Magnesium ammonium phosphate (MAP) Most common type in dogs Also in cats and ruminants Females are most commonly affected Bacterial ureases -> pH h -> struvite solubility i

Oxalate stones consist of calcium oxalate development is not well understood caused by hypercalciuria and hyperoxaluria dietary magnesium and citrate inhibit formation common in male dogs and rare in ruminants (plants -> acute death), related to diet in cats

Urate stones contain either ammonium urate with some uric acid and phosphate or sodium urate often in male Dalmatians (inherited) incomplete conversion of uric acid to allantoin in liver -> uric acid in urine also dogs with liver disorders portosystemic shunts, cirrhosis

Cystine stones Consist of pure cystine Occur in dogs, rarely in cats may also contain calcium oxalate, struvite and complex urates Occur in dogs, rarely in cats Almost exclusively in males Inborn error of metabolism -> defective proximal tubular reabsorption from glomerular filtrate -> high levels of urinary cystine

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