Veterinary Medicine - July 2008 - (Page 400)

Feline hypercalcemia PEER-REVIEWED organ dysfunction. Carefully evaluate the leukogram for abnormal cell distribution or morphology, which indicates lymphoma or leukemia. 4. Serum chemistry proﬁle Since hypercalcemia is both a cause and consequence of renal failure, markers of kidney function (blood urea nitrogen [BUN] and creatinine concentrations) are of particular interest. In general, only severe hypercalcemia is thought to cause renal injury; mild hypercalcemia in an azotemic patient is more likely to be secondary to kidney disease. It is important to measure iCa concentrations in azotemic cats before starting a complex work-up, as elevations in tCa concentrations without increases in iCa concentrations are common in this population.4 Serum phosphorus concentrations often indicate the cause of hypercalcemia. Hyperphosphatemia suggests intrinsic renal failure, vitamin D toxicosis, or osteolytic disease. In contrast, serum phosphorus is generally subnormal in cats with hyperparathyroidism, which may explain the low incidence of renal compromise reported in these individuals.8 In addition, the serum chemistry pro le may indicate liver disease (increased liver enzyme activities, hyperbilirubinemia) or gastrointestinal tract dysfunction (hypoalbuminemia or hypocholesterolemia). Investigate any abnormalities. astinal region, and scrutinize all bony structures for lytic lesions. 8. Abdominal radiography Although soft tissue changes are more easily identi ed with ultrasonography than with abdominal radiography, you can readily identify calculi in the kidneys, ureters, or the urinary bladder by using abdominal radiography. In addition, distinctive lytic bony lesions may be noted in the vertebrae of cats with multiple myeloma. 5. Thyroxine (T4) concentration Measure serum T4 concentration in any patient more than 7 years old or in any cat showing signs of hyperthyroidism. A total T4 concentration is generally suf cient, but equivocal results can be investigated with free T4 measurement. Cats with hyperthyroidism often have increased PTH concentrations. This elevation may be an appropriate physiologic response to increased calciuresis, but it can certainly confuse patient evaluation.9 Hypercalcemia (based on tCa concentration) was reported in two hyperthyroid cats, but no direct association was demonstrated and no information was provided about reversibility.1 9. Abdominal ultrasonography A scan to look for organomegaly, lymphadenopathy, bladder tumors, or other masses is a logical part of the hypercalcemic work-up. Any lesions should be aspirated or biopsied. As calcium oxalate uroliths are commonly noted in hypercalcemic cats, pay close attention to the renal pelves and ureters.10,11 If you have any concerns about ureteral obstruction, an abdominal radiographic examination may assist with calculi detection. 10. PTH concentration Serum PTH concentrations will be low in cats with neoplasia, vitamin Drelated toxicosis, or osteolytic disease. Although elevated PTH concentrations are the hallmark of primary hyperparathyroidism, PTH concentrations must be interpreted in conjunction with iCa concentrations.8 In cats with appropriate feedback mechanisms, elevated iCa concentrations suppress PTH release. Consequently, high normal PTH concentrations are inappropriate in patients with elevated iCa concentrations. Cats with renal failure have variable PTH concentrations, but iCa concentrations are generally normal. Patients with idiopathic hypercalcemia are expected to have low normal PTH concentrations. 6. Urinalysis Although profound polydipsia is not commonly noted in cats with hypercalcemia, urine concentration may be lower than expected (speci c gravity < 1.040). Isosthenuria may indicate intrinsic renal failure, but it has been noted in cats with severe hypercalcemia for many reasons. Perform a urine sediment examination in all cats with hypercalcemia. Calcium oxalate urolithiasis is commonly noted in hypercalcemic cats, and morbidity may occur from urinary tract obstruction and infection.5,10,11 7. Thoracic radiography A three-view thoracic radiographic examination (right and left lateral plus ventrodorsal or dorsoventral) is appropriate since both primary and metastatic neoplasia may cause hypercalcemia. Pay particular attention to the medi- 11. PTH-related protein concentration Many tissues synthesize a protein with marked similarities to endogenous PTH. 400 July 2008 VETERINARY MEDICINE http://stokespharmacy.com http://stokespharmacy.com

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Veterinary Medicine - July 2008 Contents Leading Off Practical Matters Idea Exchange Clarification Dental Corner The Diagnostic Approach to Hematuria Guidelines for Evaluating Hypercalcemic Cats CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - July 2008

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