Nephroliths in a cat: What is your diagnosis
Jul 01, 2002
According to the owner, there was no evidence of dysuria or pollakiuria. Physical examination revealed no abnormalities. Results of a CBC and serum biochemical profile were normal (urea nitrogen concentration = 29 mg/dl, creatinine concentration = 1.5 mg/dl, calcium concentration = 9.9 mg/dl, and phosphorus concentration = 3.7 mg/dl). Analysis and aerobic culture of a voided urine sample revealed the following results:
Mineral composition In your opinion, what is the mineral composition of the nephroliths? You may find the following information to be helpful in formulating your answer.
Please examine the radiograph again and note the shape and location of the nephroliths. Their linear shape and distribution suggest that they are located in the diverticula of the renal pelves. Next, examine Figure 2. Note that the appearance of the nephroliths removed from one of the kidneys is similar to dried blood clots. Microscopic evaluation of stained sections of the nephroliths confirm that they are primarily composed of red cells and proteinaceous material (75 percent) and mineral salts containing calcium (25 percent; Figure 3). Evaluation of the nephroliths by polarizing light microscopy and infrared spectrophotometry reveal that their mineral component is calcium phosphate.
Less commonly they have been observed in dogs (Figure 4). Probable risk factors for formation and retention of blood clots in the urinary tract include:
Mechanism of precipitation We speculate that the mechanism of precipitation of calcium phosphate in the blood clots is similar to dystrophic mineralization that may occur in devitalized tissue anywhere in the body. In our experience, affected cats and dogs were not hypercalcemic or hyperphosphatemic.
If hematuria persists, therapeutic strategies designed to reduce urine concentration and increase the flow of urine through the excretory pathway may reduce the concentration of factors that promote formation of clots. Consumption of diets designed to minimize urinary excretion of excess calcium, phosphorus and acid catabolites might reduce mineralization of blood clots.
Despite persistent idiopathic renal hematuria, the nephroliths in the cat described at the beginning of this Diagnote remained inactive (did not increase in number or size, or cause outflow obstruction, or result in bacterial UTI) during a three-year period of evaluation.
Serial evaluation of CBC's during this period revealed no evidence of anemia.
To obtain further information about quantitative analysis of uroliths from the Minnesota Urolith Center, FAX your request to (612) 624-0751.