Effect of Feeding an Iodine‐Restricted Diet in Cats with Spontaneous Hyperthyroidism

Background

Exclusive feeding of an iodine‐restricted diet has been proposed as a method for controlling clinical manifestations of hyperthyroidism in hyperthyroid cats.

Objectives

To determine the effect of feeding an iodine‐restricted diet on TT4 concentrations and clinical signs in cats with spontaneous hyperthyroidism.

Animals

Forty‐nine client‐owned cats with spontaneous hyperthyroidism.

Methods

Retrospective case series. Hyperthyroid cats were exclusively fed a commercially available iodine‐restricted diet. Clinical response was assessed by change in weight and heart rate and serum TT4, blood urea nitrogen (BUN), and creatinine concentrations at various times during dietary management (21–60 days, 60–180 days).

Results

Serum TT4 normalized in 20/48 cats (42%) and 39/47 cats (83%) at 21–60 days and 61–180 days, respectively. Cats in which the TT4 concentrations were still above reference range at 21–60 days had a significantly higher starting TT4 than those that normalized their TT4 levels during the same time period (P = .038). Body weight did not significantly increase (P = .34) nor heart rate decrease (P = .64) during the study. There was a significant decrease in serum creatinine (P = .028). Cats in the low reference range for serum TT4 concentrations did not have a significant increase in body weight (P = .41) nor creatinine (P = .54) when compared to those with high reference range.

Conclusions and Clinical Importance

Restricted‐iodine diets were effective at maintaining serum TT4 concentrations within reference ranges for a majority of cats with spontaneous hyperthyroidism over 1 year, although not all clinical signs of hyperthyroidism improved.     

Evaluation of Serum Thyroid‐Stimulating Hormone Concentration as a Diagnostic Test for Hyperthyroidism in Cats

Background

In humans, measurement of serum thyroid‐stimulating hormone (TSH) concentration is commonly used as a first‐line discriminatory test of thyroid function. Recent reports indicate that canine TSH (cTSH) assays can be used to measure feline TSH and results can help diagnose or exclude hyperthyroidism.

Objectives

To investigate the usefulness of cTSH measurements as a diagnostic test for cats with hyperthyroidism.

Animals

Nine hundred and seventeen cats with untreated hyperthyroidism, 32 euthyroid cats suspected of having hyperthyroidism, and 131 clinically normal cats.

Methods

Prospective study. Cats referred to the Animal Endocrine Clinic for suspected hyperthyroidism were evaluated with serum T₄, T₃, free T₄ (fT ₄), and TSH concentrations. Thyroid scintigraphy was used as the gold standard to confirm or exclude hyperthyroidism.

Results

Median serum TSH concentration in the hyperthyroid cats (<0.03 ng/mL) was significantly (P < .001) lower than concentrations in clinically normal cats (0.05 ng/mL) or euthyroid cats with suspected thyroid disease (0.06 ng/mL). Only 18 (2.0%) hyperthyroid cats had measurable TSH concentrations (≥0.03 ng/mL), whereas 114 (69.9%) of the 163 euthyroid cats had detectable concentrations. Combining serum TSH with T₄ or fT ₄ concentrations lowered the test sensitivity of TSH from 98.0 to 97.0%, but markedly increased overall test specificity (from 69.9 to 98.8%).

Conclusions and Clinical Importance

Serum TSH concentrations are suppressed in 98% of hyperthyroid cats, but concentrations are measurable in a few cats with mild‐to‐moderate hyperthyroidism. Measurement of serum TSH represents a highly sensitive but poorly specific test for diagnosis of hyperthyroidism and is best measured in combination with T₄ and fT ₄.     

Treatment of Ionized Hypercalcemia in 12 Cats (2006–2008) Using PO‐Administered Alendronate

Background

Long‐term treatment of cats with ionized hypercalcemia using alendronate has not been evaluated.

Hypothesis/Objectives

Alendronate is well tolerated in treatment of ionized hypercalcemia in cats.

Animals

A total of 12 cats with ionized hypercalcemia.

Methods

Prospective study of 12 cats with ionized hypercalcemia of idiopathic origin was identified by telephone and email communication with a convenience sample of consulting veterinarians. Cats were treated with alendronate at a dose of 5–20 mg per feline PO q7d. Serum ionized calcium concentration (iCa) was measured before beginning treatment with alendronate, and after 1, 3, and 6 months of treatment. Alendronate dosage was adjusted according to iCa. Evaluation included physical examination, CBC, biochemistry profile, and diagnostic imaging. The owners and referring veterinarians were questioned about any observed adverse effects. The Wilcoxon matched‐pairs signed rank test was used to compare baseline iCa to iCa at different time periods.

Results

Alendronate treatment resulted in a decrease in iCa in all 12 cats. The median percentage change in iCa was −13.2%, −15.9%, and −18.1% (range, −29.6 to +7.6; −30.5 to −1.9; −45.8 to +1.5%) at the 1, 3, and 6 month time points, respectively. Baseline iCa was significantly different from 1 month (P = .0042), 3 months (P = .0005), and 6 months (P = .0015). No adverse effects were reported for any of the cats.

Conclusions and Clinical Importance

Alendronate was well tolerated and decreased iCa in most cats for the 6‐month period of observation.     

Efficacy of Low‐ and High‐Dose Trilostane Treatment in Dogs (< 5 kg) with Pituitary‐Dependent Hyperadrenocorticism

Background

Trilostane is commonly used to treat pituitary‐dependent hyperadrenocorticism (PDH) in dogs. There are differing opinions regarding the dose and frequency of trilostane administration in dogs with PDH.

Objectives

To compare the efficacy of 2 trilostane protocols in the treatment of dogs with PDH.

Animals

Sixteen client‐owned dogs with PDH and a body weight <5 kg.

Methods

Prospective observational study. Group A (n=9; low‐dose treatment group) received 0.78 ± 0.26 mg of trilostane/kg PO every 12 h and group B (n = 7; high‐dose treatment group) 30 mg of trilostane/dog PO every 24 h. All of the dogs were reassessed at 2, 4, 8, 12, 16, and 24 weeks after the initiation of treatment.

Results

An improvement in both ACTH‐stimulated serum cortisol concentrations and clinical signs occurred more slowly in group A than in group B; however, after 20 weeks of treatment, 2/7 dog in group B had clinical signs and abnormal laboratory findings consistent with hypoadrenocorticism. At 24 weeks, an improvement in the clinical findings of all of the dogs in both groups was detected.

Conclusions and clinical importance

In dogs with PDH, twice‐daily administration of low‐dose trilostane is an effective approach to the management of PDH. In addition, our results suggest fewer potential adverse effects if trilostane is administered twice daily in the lower dose.     

A phase II study to evaluate the toxicity and efficacy of alternating CCNU and high‐dose vinblastine and prednisone (CVP) for treatment of dogs with high‐grade,metastatic or nonresectable mast cell tumours

Safety and efficacy of a protocol of alternating 1‐(2‐chloroethyl)‐3‐cyclohexyl‐1‐nitrosourea (CCNU; 70 mg m^?2) and vinblastine (3.5 mg m^?2), and prednisone (1–2 mg kg^?1; CVP) in dogs with mast cell tumours (MCT) were evaluated. A total of 17 dogs had nonresectable MCTs and 35 received CVP as adjunctive treatment to locoregional control of metastatic MCTs or grade III MCTs. Neutropenia with fever occurred in 8% of dogs after treatment with vinblastine and in 2% after treatment with CCNU. Persistent elevation of serum alanine transaminase, suggestive of hepatotoxicity, occurred in 9% of the dogs. Response rate in dogs with nonresectable MCTs was 65%; five achieved a complete response (median, 141 days) and six achieved a partial response (median, 66 days). Overall median progression‐free survival (PFS) time in dogs treated in the adjuvant setting was 489 days. Dogs with grade III MCTs had shorter PFS compared with dogs with metastatic grade II MCTs (190 days versus 954 days; P < 0.001). Phase III studies are needed to provide reliable information about the comparative efficacy of this protocol.