Veterinary Medicine - July 2008 - (Page 394)

Feline hypercalcemia PEER-REVIEWED urolithiasis (n = 11), and primary hyperparathyroidism (n = 4). However, iCa concentrations were not measured, so some of these may not have been true feline hypercalcemia cases. In fact, many cats with chronic kidney disease have normal iCa concentrations and, thus, are not truly hypercalcemic.4 Cats with neoplasia had higher serum calcium concentrations (13.5 ± 2.5 mg/dl) than cats with renal failure did (11.5 ± 0.5 mg/dl).1 Eight of the 11 cats with urolithiasis had calcium oxalate stones con rmed at surgery.1 An underlying cause of hypercalcemia was not identi ed in any of the cats with urolithiasis. Based on the exclusion of other recognized causes, these patients t the criteria for idiopathic hypercalcemia.5 This term was rst proposed in the late 1990s and is now applied to any cat with unexplained, repeatable hypercalcemia. Since it is a diagnosis of exclusion, every reasonable effort must be made to rule out other likely causes. The SHIRT list (Table 3) is a mnemonic devised to help you remember the common causes of feline hypercalcemia. Table 4 summarizes the classic serum chemistry pro le ndings in cats with the commonly identi ed causes of hypercalcemia and demonstrates the parameters expected in idiopathic cases. TABLE 4 TABLE 3 Common Causes of Feline Hypercalcemia: SHIRT S Spurious • Lipemia, hemolysis • Always verify before proceeding Hyperparathyroidism Idiopathic Renal failure • Most cats have normal iCa concentrations despite having elevated tCa concentrations Tumors • Lymphoma • Carcinoma • Multiple myeloma H I R T patients (tCa > 15 mg/dl) or those with a serum calcium-phosphorus product > 70, immediate intervention to lower serum calcium concentrations may be necessary.6 In such cases, it is imperative to establish a diagnosis quickly, and it is appropriate to investigate all likely causes simultaneously. In many cases, a database that includes a complete history, a physical examination, retroviral testing, a complete blood count, a serum chemistry pro le, a urinalysis, thoracic and abdominal radiographic examinations, and an abdominal ultrasonographic examination will establish a preliminary diagnosis. In other cases, speci c evaluation of calcium homeostasis may be necessary (Table 5). The following is a brief review of the standard diagnostic tests, and an algorithm (Figure 1) is also presented as a guide. 1. Physical examination APPROACH TO THE HYPERCALCEMIC PATIENT In cases of mild (tCa < 13 mg/dl) and moderate (tCa = 13 to 15 mg/dl) hypercalcemia, therapy can be delayed while the diagnosis is pursued in a logical, stepwise fashion.2 In severely hypercalcemic Since neoplasia is the most likely cause of moderate to severe hypercalcemia, a thorough physical examination is essential, paying particular attention to the mammary glands, peripheral lymph nodes, and skin. Abdominal palpation may reveal organomegaly, or thoracic auscultation may point toward pulmonary, mediastinal, or pleural Biochemical Parameters* Expected with the Common Causes of Feline Hypercalcemia Disorder Renal failure Primary hyperparathyroidism Neoplasia (nonosteolytic) Idiopathic Vitamin D toxicosis tCa N, , N, iCa , occ N, occ N, occ N N, Creatinine Phosphorus ,N ,occ , occ N N, N PTH occ , occ N PTH-rP N N ,N N N Vitamin D** N, N N N *These parameters are generalizations. Individual cases may not ﬁt these patterns. **25-hydroxycholecalciferol = increased; = decreased; N = normal; occ = occasional; PTH = parathyroid hormone; PTH-rP = parathyroid hormone-related protein 394 July 2008 VETERINARY MEDICINE

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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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