Idiopathic hypercalcemia in cats

Unexplained hypercalcemia has been increasingly recognized in cats since 1990. In some instances, hypercalcemia has been associated with calcium oxalate urolithiasis, and some affected cats have been fed acidifying diets. We studied the laboratory findings, clinical course, and treatment of 20 cats with idiopathic hypercalcemia. Eight (40%) of the cats were longhaired and all 14 cats for which adequate dietary history was available had been fed acidifying diets. Clinical signs included vomiting (6 cats), weight loss (4 cats), dysuria (4 cats), anorexia (3 cats), and inappropriate urinations (3 cats). Hypercalcemia was mild to moderate in severity. and serum parathyroid hormone concentrations were normal or low. Serum concentrations of phosphorus, parathyroid hormone-related peptide, 25-hydroxycholecalciferol, and calcitriol were within the reference range in most cats. Diseases commonly associated with hypercalcemia (eg, neoplasia, primary hyperparathyroidism) were not identified despite thorough medical evaluations and long-term clinical follow-up. Azotemia either did not develop (10 cats) or developed after the onset of hypercalcemia (3 cats), suggesting that renal failure was not the cause of hypercalcemia in affected cats. Seven of 20 cats (35%) had urolithiasis, and in 2 cats uroliths were composed of calcium oxalate. Subtotal parathyroidectomy in 2 cats and dietary modification in 11 cats did not result in resolution of hypercalcemia. Treatment with prednisone resulted in complete resolution of hypercalcemia in 4 cats.     

Prediction of serum ionized calcium concentration by serum total calcium measurement in cats

Feline serum samples (n = 434) were classified as hypercalcemic, normocalcemic, or hypocalcemic based on both total calcium (tCa) and ionized calcium (iCa) concentrations. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive diagnostic likelihood ratio (PDLR), and negative diagnostic likelihood ratio (NDLR) were calculated for prediction of hypercalcemia and hypocalcemia in all samples, in hypoalbuminemic cats, and in those with chronic renal failure (CRF) as compared with cats that had other conditions. Diagnostic discordance in prediction of iCa using tCa was 40%. Sensitivity of tCa in prediction of ionized hypercalcemia was low and specificity was high. The PDLR for prediction of ionized hypercalcemia or hypocalcemia was low in all cats, especially in those with CRF. Due to the high level of diagnostic discordance, tCa should not be used to predict iCa concentration. Concentration of iCa should be measured directly when accurate assessment of calcium status is needed.     

Uses and effectiveness of pamidronate disodium for treatment of dogs and cats with hypercalcemia

Uncorrected hypercalcemia can cause clinical signs such as polyuria, polydipsia, vomiting, diarrhea, lethargy, and depression and contributes to the development of primary renal failure and soft tissue mineralization. Treatment of hypercalcemia includes diagnosis and treatment of the underlying disease process and some combination of excracellular fluid volume expansion by administration of fluids intravenously and administration of glococorticosteroids, salmon calcitonin, and furosemide. Bisphosphonates such as pamidronate disodium also may be safe and effective in the treatment of hypercalcemia. The purpose of our study was to characterize the efficacy and safety of pamidronate in the treatment of hypercalcemia attritutable to several different disease processes in the dog and cat. Seven dogs and 2 cats were administered pamidronate at a dose of 1.05-2.0 mg/kg IV for a variety of disease processes, including neoplasia (n = 4), calcipotriene toxicity (n = 3), nocardiosis (n = 1), and idiopathic hypercalcemia with chronic renal failure (n = 1). In all the animals, IV pamidronate administration rapidly decreased serum calcium concentrations without evident toxicosis. Two animals received pamidronate several times without obvious toxicosis. On the basis of the findings in our retrospective study, pamidronate may be a safe and effective drug with which to lower both serum total and ionized calcium concentrations in patients with hypercalcemia arising from a wide variety of underlying disease processes.     

Effects of hypercalcemia on serum concentrations of magnesium, potassium, and phosphate and urinary excretion of electrolytes in horses

OBJECTIVE: To determine effects of experimentally induced hypercalcemia on serum concentrations and urinary excretion of electrolytes, especially ionized magnesium (iMg), in healthy horses. ANIMALS: 21 clinically normal mares. PROCEDURES: Horses were assigned to 5 experimental protocols (1, hypercalcemia induced with calcium gluconate; 2, hypercalcemia induced with calcium chloride; 3, infusion with dextrose solution; 4, infusion with sodium gluconate; and 5, infusion with saline [0.9% NaCl] solution). Hypercalcemia was induced for 2 hours. Dextrose, sodium gluconate, and saline solution were infused for 2 hours. Blood samples were collected to measure serum concentrations of electrolytes, creatinine, parathyroid hormone, and insulin. Urine samples were collected to determine the fractional excretion of ionized calcium (iCa), iMg, sodium, phosphate, potassium, and chloride. RESULTS: Hypercalcemia induced by administration of calcium gluconate or calcium chloride decreased serum iMg, potassium, and parathyroid hormone concentrations; increased phosphate concentration; and had no effect on sodium, chloride, and insulin concentrations. Hypercalcemia increased urinary excretion of iCa, iMg, sodium, phosphate, potassium, and chloride; increased urine output; and decreased urine osmolality and specific gravity. Dextrose administration increased serum insulin; decreased iMg, potassium, and phosphate concentrations; and decreased urinary excretion of iMg. Sodium gluconate increased the excretion of iCa, sodium, and potassium. CONCLUSIONS AND CLINICAL RELEVANCE: Hypercalcemia resulted in hypomagnesemia, hypokalemia, and hyperphosphatemia; increased urinary excretion of calcium, magnesium, potassium, sodium, phosphate, and chloride; and induced diuresis. This study has clinical implications because hypercalcemia and excessive administration of calcium have the potential to increase urinary excretion of electrolytes, especially iMg, and induce volume depletion.     

Hypercalcemia in two cats with squamous cell carcinomas

Hypercalcemia was identified in 2 cats with squamous cell carcinomas. One cat was referred because of multiple cutaneous tumors; the second cat had metastatic disease from an oral squamous cell carcinoma. In both cats, serum immunoreactive midmolecule parathyroid hormone concentration was within the range determined for clinically normal cats. The high serum calcium concentration in these cats may have resulted from the neoplastic disease, as evidenced by the reduction in serum calcium concentration after decrease in tumor size in response to treatment, and by failure to identify other known causes of hypercalcemia.     

Serum concentrations of parathyroid hormone and 25-OH vitamin D3 in cats with urethral obstruction

Objective: To measure serum parathyroid hormone (PTH) and 25‐hydroxyvitamin D₃ concentrations in cats with urethral obstruction. Design: Prospective single cohort study. Setting: University affiliated veterinary teaching hospital. Animals: Male cats with urethral obstruction. Interventions: Routine blood samples drawn from male cats with urethral obstruction. Measurements and main results: Measured variables included blood gas parameters, plasma sodium, potassium, chloride, and ionized calcium concentrations, as well as serum blood urea nitrogen, creatinine, phosphorus, PTH, and 25‐hydroxyvitamin D₃ concentrations. PTH was inversely correlated with ionized calcium and positively correlated with serum phosphorus. No discernable relationship could be found between 25‐hydroxyvitamin D₃ and any of the measured parameters. Conclusions: Lack of parathyroid response does not appear to be the underlying mechanism for ionized hypocalcemia in cats with urethral obstruction.     

Effect of sodium bicarbonate infusions on ionized calcium and total calcium concentrations in serum of clinically normal cats

The effects of sodium bicarbonate (0.5 mEq/kg of body weight, 1.0 mEq/kg, 2.0 mEq/kg, and 4.0 mEq/kg) on ionized and total calcium concentrations were determined in clinically normal cats. Also, serum pH, whole blood pH, and serum albumin, serum total protein, and serum phosphorus concentrations were measured. Intravenous administration of sodium bicarbonate to awake cats decreased serum ionized calcium and serum total calcium concentrations. All dosages of sodium bicarbonate were associated with significant decreases of serum ionized calcium concentration. This effect lasted for greater than 180 minutes when cats were given 2.0 mEq/kg or 4.0 mEq/kg. When cats were given 4 mEq of sodium bicarbonate/kg, serum ionized calcium concentration was significantly decreased, compared with that when cats were given lower doses, but only at 10 minutes after infusion. After sodium bicarbonate infusion, serum total calcium concentration, measured by ion-specific electrode and colorimetry, was lower than baseline values at most of the times evaluated. Decreases in serum ionized calcium and serum total calcium concentrations can be attributed only in part to an increase in serum or whole blood pH and to a decrease in serum protein concentration. Serum total calcium concentrations measured by ion-specific electrode and by colorimetry were positively correlated, but the variability was high. Only 44% of the variability in serum ionized calcium concentration could be predicted when serum total calcium, albumin, total protein, phosphorus, and bicarbonate concentrations and pH were considered.     

Hypercalcemia following renal transplantation in a cat

An 11-year-old 3.0-kg (6.6-lb) neutered male Persian was referred for renal transplantation. Serum total calcium concentration was slightly high prior to surgery, but the week after surgery, total and ionized calcium concentrations were extremely high, and a small mass was palpable on the right side of the trachea at the level of the thyroid and parathyroid glands. Exploratory surgery of the ventral aspect of the neck was performed, and a right external parathyroid mass was removed. One hour after surgery, the serum ionized calcium concentration was within reference limits, and the serum calcium concentration remained normal for the next 14 months without any specific treatment. The gross and histologic appearance of the mass, combined with the rapid decrease in serum calcium concentration following its removal, confirmed that the mass was a functional parathyroid adenoma. Although a common postoperative complication in people, hypercalcemia following renal transplantation appears to be a rare complication in cats. Surgery should be considered if the condition is a result of a parathyroid adenoma.     

Ionized Hypercalcemia in Dogs: A Retrospective Study of 109 Cases (1998–2003)

Background: Serum hypercalcemia in dogs has been reported in association with a variety of diseases. Serum-ionized calcium (iCa) concentration is a more accurate measure of hypercalcemia than total serum calcium or corrected serum calcium concentrations. The severity of hypercalcemia has been utilized to suggest the most likely differential diagnosis for the hypercalcemia.
Hypothesis: Diseases causing ionized hypercalcemia may be different than those that cause increases in total or corrected serum calcium concentrations. The severity of ionized hypercalcemia in specific diseases cannot be used to determine the most likely differential diagnosis for ionized hypercalcemia.
Animals: One-hundred and nine client-owned dogs with a definitive cause for their ionized hypercalcemia evaluated between 1998 and 2003 were included in this study.
Methods: Retrospective, medical records review.
Results: Neoplasia, specifically lymphosarcoma, followed by renal failure, hyperparathyroidism, and hypoadrenocorticism were the most common causes of ionized hypercalcemia. Dogs with lymphoma and anal sac adenocarcinoma have higher serum iCa concentrations than those with renal failure, hypoadrenocorticism, and other types of neoplasia. The magnitude of serum-ionized hypercalcemia did not predict specific disease states.
Conclusions and Clinical Importance: Serum-ionized hypercalcemia was most commonly associated with neoplasia, specifically lymphosarcoma. Although dogs with lymphosarcoma and anal sac adenocarcinoma had higher serum iCa concentrations than dogs with other diseases, the magnitude of the serum iCa concentration could not be used to predict the cause of hypercalcemia. Total serum calcium and corrected calcium concentrations did not accurately reflect the calcium status of the dogs in this study.     

Hypercalcemia in cats: a retrospective study of 71 cases (1991-1997)

A retrospective study was conducted to characterize the diseases, clinical findings, and clinicopathologic and ultrasonographic findings associated with hypercalcemia (serum calcium concentration >11 mg/dL) in 71 cats presented to North Carolina State University Veterinary Teaching Hospital. The 3 most common diagnoses were neoplasia (n = 21), renal failure (n = 18), and urolithiasis (n = 11). Primary hyperparathyroidism was diagnosed in 4 cats. Lymphoma and squamous cell carcinoma were the most frequently diagnosed tumors. Calcium oxalate uroliths were diagnosed in 8 of 11 cats with urolithiasis. Cats with neoplasia had a higher serum calcium concentration (13.5 ± 2.5 mg/dL) than cats with renal failure or urolithiasis and renal failure (11.5 ± 0.4 mg/dL; P <.03). Serum phosphorus concentration was higher in cats with renal failure than in cats with neoplasia ( P < .004). Despite the fact that the majority of cats with uroliths were azotemic, their serum urea nitrogen and creatinine concentrations and urine specific gravity differed from that of cats with renal failure. Additional studies are warranted to determine the underlying disease mechanism in the cats we identified with hypercalcemia and urolithiasis. We also identified a small number of cats with diseases that are not commonly reported with hypercalcemia. Further studies are needed to determine whether an association exists between these diseases and hypercalcemia, as well as to characterize the underlying pathophysiologic mechanism for each disease process.     

Functional analysis of ectopic parathyroid activity in cats

The ability of ectopic parathyroid tissue to support calcium homeostasis was evaluated by measuring serum concentrations of calcium, phosphorus, albumin, magnesium, and parathyroid hormone before and for 12 weeks after bilateral thyroparathyroidectomy in 14 cats. During the immediate postoperative period, significant decrease was observed in serum calcium, magnesium, and parathyroid hormone (PTH) concentrations. Serum PTH concentration remained subnormal and did not significantly increase during the 12-week observation period. Despite persistent hypoparathyroidism, serum calcium and magnesium concentrations gradually increased. Ectopic parathyroid tissue is not capable of maintaining normal serum calcium concentration immediately after thyroparathyroidectomy. Serum calcium concentration gradually normalizes after thyroparathyroidectomy, apparently by means of a PTH-independent mechanism.     

Hepatotoxicity of stanozolol in cats

OBJECTIVE: To determine hepatotoxicity of stanozolol in cats and to identify clinicopathologic and histopathologic abnormalities in cats with stanozolol-induced hepatotoxicosis. DESIGN: Clinical trial and case series. ANIMALS: 12 healthy cats, 6 cats with chronic renal failure, and 3 cats with gingivitis and stomatitis. PROCEDURES: Healthy cats and cats with renal failure were treated with stanozolol (25 mg, i.m., on the first day, then 2 mg, p.o., q 12 h) for 4 weeks. Cats with gingivitis were treated with stanozolol at a dosage of 1 mg, p.o., every 24 hours. RESULTS: Most healthy cats and cats with renal failure developed marked inappetence, groomed less, and were less active within 7 to 10 days after initiation of stanozolol administration. Serum alanine transaminase (ALT) activity was significantly increased in 14 of 18 cats after stanozolol administration, but serum alkaline phosphatase activity was mildly increased in only 3. Four cats with serum ALT activity > 1,000 U/L after only 2 weeks of stanozolol administration had coagulopathies; administration of vitamin K resolved the coagulopathy in 3 of the 4 within 48 hours. All 18 cats survived, and hepatic enzyme activities were normal in all cats tested more than 4 weeks after stanozolol administration was discontinued. Two of the 3 cats with gingivitis developed evidence of severe hepatic failure 2 to 3 months after initiation of stanozolol treatment; both cats developed coagulopathies. Histologic evaluation of hepatic biopsy specimens from 5 cats revealed diffuse hepatic lipidosis and cholestasis without evidence of hepatocellular necrosis. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that stanozolol is hepatotoxic in cats.     

Ionized and total serum magnesium concentrations in feline renal transplant recipients

OBJECTIVE: To measure the blood concentrations of total and ionized serum magnesium in feline renal transplant recipients and to determine if there was a correlation between these concentrations and the development of neurological disorders after renal transplantation. STUDY DESIGN: Prospective clinical study. ANIMALS: Fourteen client-owned cats undergoing renal transplantation as a treatment for renal failure. Ten healthy adult cats were used to establish normal electrolyte concentrations. METHODS: Total and ionized serum magnesium as well as potassium and ionized calcium concentrations were measured in 14 renal transplant recipients at five intervals: preoperatively; immediately postoperatively; and 24, 48, and 120 hours postoperatively. The mean values from all 14 cats over each time interval were compared with the normal range. The serum concentration of these electrolytes, particularly magnesium, was evaluated in relation to the occurrence of neurological complications. RESULTS: Ninety-four percent of all ionized serum magnesium concentrations measured in clinical patients were below normal. Ninety percent of all total serum magnesium concentrations were within the normal range, and no cats had abnormally low total serum magnesium concentrations at any time. All clinical patients were hypocalcemic at all intervals. Sixty-six percent of all serum potassium concentrations were below normal. One cat in the study group experienced neurological problems, including seizures, in the immediate postoperative period. The signs appeared to be related to hypertension and responded to appropriate therapy. All electrolyte concentrations in this cat, including ionized magnesium, were within the same range of values as other clinical patients. CONCLUSIONS: Ionized serum magnesium concentrations are decreased in feline renal transplant recipients in the perioperative period; however, hypomagnesemia would not appear to be directly related to the development of neurological disorders. None of the study patients were hypomagnesemic when total serum magnesium concentrations were measured over the same intervals. In addition, ionized serum calcium concentrations and serum potassium concentrations are below normal in the perioperative period. CLINICAL SIGNIFICANCE: The specific clinical significance of these abnormalities is unknown. It is possible that the profound weakness and depression that is commonly seen in feline renal transplant recipients in the immediate postoperative period may be improved by supplementation with these electrolytes. Further work is needed to understand the implications of these abnormalities.     

Presumptive increase in protein‐bound serum calcium in a dog with multiple myeloma

Abstract: An 11‐year‐old male castrated Australian Shepherd was presented with a history of lethargy, panting, and weight loss for 1 month. Physical examination revealed a moderately enlarged spleen. Laboratory abnormalities included thrombocytopenia and marked hypercalcemia, with hyperglobulinemia, hypoalbuminemia, and a monoclonal spike in the β‐globulin region on serum protein electrophoresis. Serum total calcium concentration was markedly increased (16.5 mg/dL, reference interval 8.9–11.4 mg/dL) but ionized calcium concentration (1.39 mmol/L) was within the reference interval (1.25–1.45 mmol/L). Isosthenuria was noted, but the dog was not polyuric or polydipsic. Serum parathyroid hormone concentration was within reference limits and parathyroid hormone‐related peptide concentration was 0 pmol/L. Radiographic findings were largely unremarkable. Results of cytologic evaluation of a fine‐needle aspirate specimen from the spleen indicated plasma cell neoplasia. Based on the results of the electrophoresis, splenic aspirates, radiographs, and hypercalcemia, a diagnosis of splenic multiple myeloma was made. The marked hypercalcemia, normal ionized calcium and parathyroid hormone concentrations, and lack of osteolytic lesions indicated a presumptive increase in protein‐bound serum calcium, likely due to binding to molecules of the paraprotein (M protein). Protein binding of calcium in dogs with multiple myeloma should be considered as a potential mechanism of elevated total serum calcium concentration.     

Evaluation of calciotropic hormones in cats with odontoclastic resorptive lesions

OBJECTIVE: To assess associations between epidemiologic and laboratory variables and calciotropic hormones in cats with odontoclastic resorptive lesions (ORLs). ANIMALS: 182 client-owned cats older than 1 year of age with oral disease. PROCEDURE: Information on medical history, behavior, living environment, and feeding management was assessed by use of a questionnaire. After induction of general anesthesia, oral examination was performed following standardized protocols and included dental probing and full-mouth radiography. Laboratory analyses included evaluation of FeLV-FIV status, serum biochemical analyses, CBC, urinalysis, and serum concentrations of intact parathyroid hormone (iPTH), parathyroid hormone-related peptide (PTHrP), 25-hydroxyvitamin D (25-OHD), free thyroxine (fT4), and ionized calcium (iCa). RESULTS: ORLs were identified in 72.5% of cats. Mandibular third premolars were the most commonly affected teeth. Cats with ORLs were significantly older (mean, 9.2 years) than cats without ORLs (mean, 6.6 years). Multivariate logistic regression analysis revealed that 25-OHD, urine specific gravity, jaw-opening reflex on probing, and missing teeth were significant variables, even after accounting for age. Cats with ORLs had significantly higher mean serum concentration of 25-OHD (112.4 nmol/L) and significantly lower mean urine specific gravity (1.0263), compared with cats without ORLs (89.8 nmol/L and 1.0366, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Results did not indicate associations between iPTH, PTHrP, or fT4 and development of ORLs. In affected cats, the importance of high serum 25-OHD and low urine specific gravity has not been determined.     

Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats

Objective-To determine whether a renal diet modified in protein, phosphorus, sodium, and lipid content was superior to an adult maintenance diet in minimizing uremic episodes and mortality rate in cats with stage 2 or 3 chronic kidney disease (CKD). Design-Double-masked, randomized, controlled clinical trial. Animals-45 client-owned cats with spontaneous stage 2 or 3 CKD. Procedures-Cats were randomly assigned to an adult maintenance diet (n = 23 cats) or a renal diet (22) and evaluated trimonthly for up to 24 months. Efficacy of the renal diet, compared with the maintenance diet, in minimizing uremia, renal-related deaths, and all causes of death was evaluated. Results-Serum urea nitrogen concentrations were significantly lower and blood bicarbonate concentrations were significantly higher in the renal diet group at baseline and during the 12- and 24-month intervals. Significant differences were not detected in body weight; Hct; urine protein-to-creatinine ratio; and serum creatinine, potassium, calcium, and parathyroid hormone concentrations. A significantly greater percentage of cats fed the maintenance diet had uremic episodes (26%), compared with cats fed the renal diet (0%). A significant reduction in renal-related deaths but not all causes of death was detected in cats fed the renal diet. Conclusions and Clinical Relevance-The renal diet evaluated in this study was superior to an adult maintenance diet in minimizing uremic episodes and renalrelated deaths in cats with spontaneous stage 2 or 3 CKD.     

Parathyroid hormone‐related protein‐induced hypercalcemia due to osteosarcoma in a cat

A 15‐year‐old castrated male mixed‐breed cat was presented with a history of sarcoma of the distal right hind limb. Biochemical analysis revealed increased concentrations of blood urea, creatinine, total calcium, ionized calcium, and parathyroid hormone‐related protein (PTHrP). The mass was removed surgically by amputation of the hind limb. Osteosarcoma was diagnosed based on histopathologic examination. All abnormal serum analyte concentrations improved immediately after surgery, including azotemia, total calcium, ionized calcium, and PTHrP. The biochemical results were attributed to osteosarcoma causing PTHrP‐induced hypercalcemia.     

Detection of parathyroid hormone-related protein in cats with humoral hypercalcemia of malignancy

Background — Increased serum parathyroid hormone‐related peptide (PTHrP) concentration is used to diagnose humoral hypercalcemia of malignancy (HHM) in humans and animals. A commercially available assay for human PTHrP has diagnostic utility in the dog, but has not been assessed in cats. Objectives — The goals of this study were to determine serum or plasma levels of PTHrP in a population of hypercalcemic cats and to determine whether increased PTHrP concentration was associated with malignancy. In addition, we validated immunoradiometric assays (IRMAs) for intact parathormone (iPTH) and PTHrP for use with feline samples. Methods — A retrospective analysis of iPTH and PTHrP results from 322 hypercalcemic cats (ionized calcium concentration >1.4 mmol/L) was performed. Immunoassays for human iPTH and PTHrP (residues 1–84) were validated using standard methods, and reference intervals were calculated using values from 31 healthy adult cats. Hypercalcemic cats were classified as parathyroid‐independent (iPTH <2.3 pmol/L), equivocal (iPTH 2.3–4.6 pmol/L), or parathyroid‐dependent (iPTH >4.6 pmol/L). Seven cats with detectable or increased PTHrP concentrations were evaluated further for underlying disease. Formalin‐fixed neoplastic tissues were immunohistochemically stained using rabbit antibody to human midregion PTHrP. Results — Assays for iPTH and PTHrP showed acceptable precision for feline samples. The reference interval for iPTH was 0.8–4.6 pmol/L and for PTHrP was <1.5 pmol/L. The majority of hypercalcemic cats (263/322, 81.7%) were parathyroid‐independent, with fewer cats in the equivocal (32/322,9.9%) and parathyroid‐dependent (27/322,8.4%) groups. In 31 (9.6%) cats, PTHrP concentration was >1.5 pmol/L (range 1.5–26.6 pmol/L). All 7 cats for which follow‐up information was available had HHM; 6 had carcinomas (4 lung carcinomas, 1 undifferentiated carcinoma, 1 thyroid carcinoma) and 1 had lymphoma. All tumors had mild to moderate positive staining for PTHrP; however, lung carcinomas from normocalcemic cats also stained positive. Conclusions — Human IRMA for PTHrP (1–84) can be used to measure PTHrP in cats. Malignancies, particularly carcinomas, appear to secrete PTHrP and induce HHM in this species. Immunohistochemistry alone cannot predict the occurrence of HHM in cats.     

Study of calcium homeostasis in feline hyperthyroidism

Thirty cats with untreated hyperthyroidism were blood sampled and their calcium homeosta-tic mechanisms and renal function assessed. The results were compared with those obtained from 38 age-matched control cats. The hyperthyroid group of cats were found to have significantly lower blood ionised calcium and plasma creatinine concentrations and significantly higher plasma phosphate and parathyroid hormone concentrations. Hyperparathyroidism occurred in 77 per cent of hyperthyroid cats, with parathyroid hormone concentrations reaching up to 19 times the upper limit of the normal range. The aetiology, significance and reversibility of hyperparathyroidism in feline hyperthyroidism remains to be established but could have important implications for both bone strength and renal function.     

Effect of long-term administration of ketoconazole in cats

Four cats given ketoconazole (30 mg/kg of body weight/day) for 30 days developed dry hair coats and weight loss. Plasma cortisol and serum cholesterol, testosterone, and progesterone did not change significantly (P greater than 0.01), and significant alterations in serum albumin, calcium, and alkaline phosphatase (P less than 0.01) did not preclude use of the drug. Serum testosterone concentrations tended to decrease after 7 days of treatment, but in 2 cats returned to near-pretreatment values by day 30 of treatment, despite continued drug administration. These results were in contrast to those reported in the dog at similar and lesser dosages of ketoconazole.