Page 2036 - Cote clinical veterinary advisor dogs and cats 4th

Urolithiasis, Struvite 1017

protein content may predispose to struvite Advanced or Confirmatory Testing
Clinical Presentation crystal formation. • Abdominal ultrasound: little benefit beyond
HISTORY, CHIEF COMPLAINT
VetBooks.ir Clinical signs may be absent. When signs are DIAGNOSIS abdominal radiography; can confirm location, Diseases and Disorders
assess kidneys for evidence of pyelonephritis
or hydronephrosis
apparent, they may include
• Hematuria
be submitted for quantitative analysis
• Pollakiuria Diagnostic Overview • Urolith analysis: retrieved stones should
Diagnosis is suspected in dogs with radiopaque
• Dysuria bladder stones, alkaline urine, and/or UTI. The (crystallography, x-ray diffraction, infrared
• Stranguria diagnosis is suspected in cats with radiopaque spectroscopy) to determine urolith type.
• Inappropriate elimination (periuria) bladder stones, alkaline urine, and/or struvite • Urolith culture: retrieved stones can be
• Rarely, systemic illness due to urinary tract crystalluria. Quantitative stone analysis is neces- cultured if urine culture obtained by cys-
obstruction, ascending infection causing sary to confirm the diagnosis and provide an tocentesis is negative.
pyelonephritis, or systemic illness that optimal treatment/prevention plan, but emperic • If urine culture negative, bladder wall culture
predisposes to UTI (e.g., diabetes mellitus) therapy may be appropriate. A global approach should be performed if stones are removed
to diagnosis and management is outlined on surgically or by cystoscopy.
PHYSICAL EXAM FINDINGS p. 1456.
Physical exam is usually unremarkable. Abnor- TREATMENT
malities may include Differential Diagnosis
• Hematuria (stains on prepuce, vulva, or • UTI Treatment Overview
hocks) • Other types of uroliths Although uncommon, urinary tract obstruction
• Painful urinary bladder • Urinary tract neoplasia requires immediate relief. In the absence of
• Palpable cystic calculi urinary obstruction, treatment consists of a
• Palpable urethral calculi (by digital rectal Initial Database stone-dissolution diet or manual removal of
exam in dogs) • CBC: unremarkable stones and treatment of UTI.
• Enlarged turgid bladder if urethral • Serum biochemistry profile (including
obstruction electrolytes): unremarkable unless urinary Acute General Treatment
• Renomegaly if secondary hydronephrosis tract obstruction (p. 1009) • Relieve urinary tract obstruction if present
• Complete urinalysis: neutral or alkaline (pp. 1175 and 1176).
Etiology and Pathophysiology (common) pH, bacteria (especially likely • Antibiotics for UTI are based on culture and
Infection-associated struvite urolithiasis (mainly in dogs), pyuria (especially likely in dogs), susceptibility results (dogs > cats [p. 232]).
dogs): hematuria (inconsistent), and crystalluria Generally, antimicrobial therapy is continued
• Bacterial urease converts urea to ammonia (inconsistent) are possible. until struvite urolith has dissolved or been
and carbonate. ○ Because storage of urine may lead to removed.
○ The most common urease-producing precipitation of struvite crystals, urine • Choose between medical dissolution and
pathogens are Staphylococcus and Proteus sediment should be examined within 1 mechanical calculi removal.
spp. hour of collection. ○ Urethral obstruction should be relieved
○ Other urease-producing pathogens include • Urine culture (identify uropathogen) and mechanically.
Enterococcus, Pseudomonas, Klebsiella, and susceptibility (influence antimicrobial therapy) ○ Mechanical removal allows urolith analysis
Ureaplasma (urease-producing Mycoplasma) • Abdominal radiographs and culture.
spp. ○ Generally radiopaque (radiopacity: struvite ○ Even large struvite uroliths can be ame-
+
• Ammonia buffers H , converting to ammo- ≥ oxalate = CaPO 4 = silica > cystine nable to medical dissolution.
+
nium (NH 4 ) and increasing urine pH. > urate) ○ Provided urethral obstruction is absent,
• Ammonium combines with phosphorus and ○ Often smooth or round in shape trial of medical dissolution before
magnesium, forming struvite crystals. ○ Most commonly located in bladder; mechanical removal is reasonable; potential
• Alkalinity decreases solubility of magnesium sometimes in urethra, ureter, or kidney drawbacks include risk of obstruction
ammonium phosphate crystals.
• Calcium phosphate carbonate (i.e., calcium
apatite) may be incorporated with infection-
associated struvite, and urease degradation
of urea results in CO 2 production; buffering
yields a carbonate ion.
• Ammonium urate also may be incorporated
with infection-associated struvite. Urease
degradation of urea results in ammonia,
and buffering yields ammonium, some of
which binds uric acid to form ammonium
urate.
• Crystals aggregate with organic material
(including viable bacteria) and combine to
form uroliths.
• Decreased presence of glycosaminoglycans
may occur in some cases of FLUTS/D.
Sterile struvite urolithiasis (mainly cats):
complex relationship of diet, water intake, 100 m
individual predisposition, and subsequent urine
pH and relative supersaturation
• Diets high in magnesium, phosphorus, UROLITHIASIS, STRUVITE One large (center) and several smaller struvite crystals are seen. Note their
calcium, chloride, and fiber with moderate characteristic rectangular coffin-lid shape.

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