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Calcium oxalate challenges in cats (Proceedings)


1) Incidence

a) Significant change over the last 30 years
      i) 1981: 78% Struvite; 1% Calcium oxalate (Minnesota Urolith Center)
      ii) 1996: 48% Struvite
      iii) 1999: 32% Struvite; 55% Calcium oxalate
      iv) 2007: 49% Struvite; 41% Calcium oxalate
b) Why the shift?
      i) Widespread dietary acidification began in the mid to late 1980s in an attempt to prevent struvite disease
           (1) As that happened, calcium oxalate urolithiasis emerged.
           (2) Idiopathic hypercalcemia has also emerged.
           (3) They may or may not be related.

2) Diagnosis

a) Non-crisis cats
      i) Most cats with kidney uroliths have no clinical signs
           (1) Possibly persistent or recurrent hematuria, usually without bacteria.
           (2) Many cats with bladder uroliths have no or mild clinical signs
                (a) Hematuria, dysuria, pollakiuria.
                (b) Red Flag: persistent or recurrent hematuria.
b) Crisis cats
      i) Ureters
           (1) Abdominal pain, lethargy, anorexia, dyspnea
           (2) Abdominal palpation may be helpful in establishing pain and localizing it to the abdomen.
      ii) Urethra
           (1) Abdominal pain, lethargy, anorexia, dysuria
           (2) Bladder palpation very helpful in establishing urethral obstruction.
c) Imaging
      i) Calcium oxalate uroliths are very dense.
      ii) They are usually easily seen on radiographs.
      iii) They are usually easily seen on ultrasound.
      iv) Size and location are factors with both.
           (1) Locations
                (a) Kidneys
                (b) Ureters *
                (c) Urinary bladder
                (d) Urethra * * If they become lodged in these locations, a crisis exists.
      v) Radiology vs. Ultrasound
           (1) The difference can be greatly influenced by image quality of both modalities.
           (2) Radiographs have the advantage of stopping motion of the abdomen permitting visualization of every structure at one time.
           (3) But, hydronephrosis cannot be appreciated on radiographs without an excretory urogram.
                (a) Hyapaque replaced by MD 76-R
                (b) Give 1-1.5 ml/kg IV
                (c) Take a series of radiographs at 3-5 minute intervals until the contrast material is seen in the ureters.
                (d) VD and lateral views essential.
                (e) Much better visualization if enema is given first.
                (f) Very high quality radiographs increase the quality of the study.
           (4) Uroliths in the ureters
                (a) Radiographs are preferred because the uroliths are often < 2 mm and occur in clusters.
                (b) Finding ureteral uroliths with ultrasound requires some (lots of) luck.
                (c) An empty bladder makes radiographs less sensitive.
           (5) Uroliths in the urethra
                (a) Easily seen with radiographs.
                (b) Usually missed with ultrasound.
           (6) Summary
                (a) Radiographs are preferred if ...
                     (i) You do not have ultrasound.
                     (ii) High quality radiographs can be made.
                     (iii) The uroliths are < 2 mm in diameter.
                     (iv) Multiple uroliths exist.
                     (v) Uroliths may be in the ureters: all cases with kidney uroliths.
                     (vi) Uroliths may be in the urethra: when dysuria exists.
d) Stone analysis
      i) The gross morphology of calcium oxalate uroliths varies greatly.
      ii) Do not try to "analyze" them with your eyes.
      iii) Analysis is essential for prognosis and dietary management.