Effect of Storage of Reconstituted Recombinant Human Thyroid-Stimulating Hormone (rhTSH) on Thyroid-Stimulating Hormone (TSH) Response Testing in Euthyroid Dogs

Effect of recombinant human thyroid stimulating hormone on radioactive iodine uptake by thyroid carcinoma in dogs

BACKGROUND

The high doses of radioiodine-131 (131I) and, subsequently, the high radioactive burden for dog and environment warrants optimization of 131I therapy in dogs with thyroid carcinoma (TC).

HYPOTHESIS/OBJECTIVES

To evaluate the effect of a revised protocol with recombinant human thyroid stimulating hormone (rhTSH) on tumor radioactive iodine uptake (RAIU) in dogs with TC.

ANIMALS

Nine client-owned dogs diagnosed with TC.

METHODS

A prospective cross-over study in which tumor RAIU was calculated and compared at 8 hours (8h-RAIU) and 24 hours (24h-RAIU) after injection of radioactive iodine-123 (123I), once with and once without rhTSH (ie, 250 μg, IM, 24 and 12 hours before 123I) in each dog. Simultaneously, serum total thyroxine (TT4) and TSH were measured at baseline (T0), and 6 (T6), 12 (T12), 24 (T24), and 48 hours (T48) after the first rhTSH administration.

RESULTS

Tumor RAIU was significantly higher at 24 hours with rhTSH compared to no rhTSH (mean difference = 8.85%, 95% CI of [1.56; 16.14]; P = .03), while this was non-significant at 8 hours (mean difference = 4.54%, 95% CI of [0.35; 8.73]; P = .05). A significant change of serum TT4 (median difference T24 - T0 = 35.86 nmol/L, interquartile range [IQR] = 15.74 nmol/L) and TSH (median difference T24 - T0 = 1.20 ng/mL, IQR = 1.55 ng/mL) concentrations occurred after administration of rhTSH (P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Recombinant human TSH could optimize 131I treatment in dogs with TC by increasing tumor RAIU and thus 131I treatment efficacy.

[Hypothyroidism in dogs: an overview]

Hypothyroidism is one of the most common endocrinopathies in dogs. In rare cases, it may be associated with further endocrinopathies. The most common combination is the con-currence of hypothyroidism and hypoadrenocorticism. The diagnosis of hypothyroidism is based on the measurement of thyroid hormones (T4/fT4) and thyroid stimulating hormone (TSH). As thyroid hormone concentrations in the blood are influenced by various factors (e. g. systemic diseases or drugs), test results must be interpreted in conjunction with complaints demonstrated by the patient. In cases when diagnosis is not definite, stimulating tests or diagnostic imaging techniques (ultrasound, scintigraphy) are advisable. Dogs with hypothyroidism should be diagnosed and treated with thyroid hormones. When addiditional clinical signs are not consistent with hypothyroidism, co-existing additional endocrinopathies need to be considered. Furthermore, when treatment fails to result in the expected clinical response, the diagnosis of hypothyroidism must be subject to critical re-evaluation. This article provides an overview of the current diagnostic and treatment methods in canine hypothyroidism.

Behavior in dogs with spontaneous hypothyroidism during treatment with levothyroxine

Background

Thyroid hormone supplementation anecdotally has been described as a valid treatment option for dogs with aggression‐related problems. However, prospective, controlled, and blinded trials evaluating behavior and neurohormonal status in hypothyroid dogs during treatment with levothyroxine are lacking.

Objective

Levothyroxine supplementation will have a significant influence on the behavior and neurohormonal status of dogs with spontaneous hypothyroidism.

Animals

Twenty client‐owned dogs diagnosed with spontaneous hypothyroidism.

Methods

This prospective study was to evaluate the behavior of dogs, which was screened at initial presentation, and after 6 weeks, and 6 months of treatment with levothyroxine (starting dosage 10 μg/kg PO q12h) using the standardized Canine Behavioral Assessment and Research Questionnaire (C‐BARQ). At each time period, circulating serotonin and prolactin (PRL) concentrations were evaluated using a commercially validated ELISA kit and heterologous radioimmunoassay, respectively.

Results

After 6 weeks of thyroid hormone supplementation, C‐BARQ scores demonstrated a significant increase in activity of hypothyroid dogs (P < .01). No significant change in any of the behavioral signs was observed after 6 months of treatment. No significant difference in circulating concentrations of serotonin (P > .99 and P = .46) and PRL (P = .99 and P = .37) were noted between the 6‐week and 6‐month periods compared with baseline.

Conclusions and Clinical Importance

The results of this study indicate increased activity of hypothyroid dogs after 6 weeks of thyroid hormone supplementation. None of the hypothyroid dogs in this cohort showed a significant change in any of the evaluated behavioral signs and neurohormonal status after 6 months of thyroid hormone supplementation.

Use of basal and TRH-stimulated plasma growth hormone concentrations to differentiate between primary hypothyroidism and nonthyroidal illness in dogs

BACKGROUND

A low plasma total thyroxine (TT₄ ) concentration in combination with a plasma TSH concentration within reference range does not distinguish between hypothyroidism and nonthyroidal illness (NTI) in dogs. Hypothyroidism is associated with TSH-releasing hormone (TRH)-induced increased release of growth hormone (GH).

HYPOTHESIS

Basal and TRH-induced plasma GH concentrations can be used to distinguish hypothyroid dogs from NTI dogs.

ANIMALS

Twenty-one dogs with signs consistent with hypothyroidism, a low plasma TT₄ concentration, and a plasma TSH concentration within reference interval.

METHODS

Case control study. Thyroid scintigraphy was performed to classify dogs as having hypothyroidism or NTI. All dogs underwent a TRH stimulation test with measurement of plasma concentrations of GH and TSH before and 30 and 45 minutes after IV administration of TRH.

RESULTS

Eleven of the dogs were classified as hypothyroid and 10 as having NTI. Basal plasma GH concentration in the hypothyroid dogs (3.2 μg/l; range, 2.0 to 12.5 μg/l) was significantly higher (p<0.001) than that in the NTI dogs (.73 μg/l; range, .45 to 2.3 μg/l), with minimal overlap, and increased (p=.009) after TRH administration in hypothyroid dogs, whereas it did not change in NTI dogs. At T=45, plasma GH concentrations in hypothyroid dogs and NTI dogs did not overlap. The plasma TSH concentration did not change significantly after TRH administration in hypothyroid dogs, whereas it increased (p<.001) in NTI dogs. At T=45, there was no overlap in percentage TSH increase from baseline between hypothyroid dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Measurement of basal plasma GH concentration and concentrations of GH and TSH after TRH stimulation can distinguish between hypothyroidism and NTI in dogs.

Pharmacokinetics of total thyroxine after repeated oral administration of levothyroxine solution and its clinical efficacy in hypothyroid dogs

Background

Oral levothyroxine (l‐T₄) supplementation is commonly used to treat hypothyroid dogs.

Objectives

Investigate the plasma profile and pharmacokinetics of total thyroxine (tT₄) after PO administration of a l‐T₄ solution and its clinical efficacy in hypothyroid dogs.

Animals

Ten dogs with naturally occurring hypothyroidism.

Methods

After hypothyroidism diagnosis and supplementation with l‐T₄ solution PO q24h at 20 μg/kg BW for minimum 4 weeks, the plasma profile and pharmacokinetics of tT₄ were determined over 34 hours and the clinical condition of the dogs was evaluated.

Results

Before dosing for pharmacokinetic evaluation, mean tT₄ concentration was 23 ± 9 nmol/L. l‐T₄ was absorbed rapidly (t_max, 5 hours), reaching a mean maximal tT₄ concentration of 56 ± 11 nmol/L. The apparent terminal half‐life was 11.8 hours. Clinical signs of hypothyroidism improved or resolved in all dogs after 4 weeks of treatment. The dosage of 20 μg/kg PO q24h was judged appropriate in 5 dogs, and 4 dogs required slight increases (9–16%). Twice daily treatment, with a 30% increase in dosage, was necessary for 1 dog.

Conclusions and Clinical Importance

The pharmacokinetics of l‐T₄ in hypothyroid dogs was similar to that reported in healthy euthyroid dogs. Clinical and hormonal responses to l‐T₄ solution were rapid in all dogs. The starting dosage of 20 μg/kg PO q24h was suitable for maintenance supplementation in 50% of the dogs, minor dosage modification was required in 4 other dogs, and treatment q12h was required in 1 dog.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

Blood-brain-barrier disruption in chronic canine hypothyroidism

BACKGROUND

Central nervous system (CNS) manifestations of hypothyroidism have been associated with cerebrovascular complications. Reports of cerebrospinal fluid (CSF) abnormalities are rare in hypothyroid dogs.

OBJECTIVE

The aim of this study was to determine if chronic hypothyroidism causes blood-brain-barrier (BBB) abnormalities that are detectable using indirect CSF biomarkers.

METHODS

The study included 18 normal, euthyroid, female mixed-breed dogs. Hypothyroidism was induced by (131) iodine administration in 9 dogs; 9 served as untreated controls. Evaluations included physical and neurologic examination, complete CSF analysis, serum and CSF protein electrophoresis, measurement of plasma vascular endothelial growth factor (VEGF) and serum S-100B concentrations, and calculation of CSF albumin quota (AQ) and were conducted at baseline and 6, 12, and 18 months after induction of hypothyroidism. Data were analyzed using repeated measures ANOVA.

RESULTS

At baseline, differences between groups were not detected for any variable. Throughout the study, controls dogs remained free of neurologic disease and had test variables that remained within reference intervals. Two hypothyroid dogs developed CNS signs during the study, and evidence of cerebrovascular disease was found at necropsy. At 12 and 18 months, the CSF total protein, VEGF, S-100B, and fractional albumin concentrations, and AQ were significantly higher (P<.04) in hypothyroid dogs than controls. Among test variables assayed in serum or plasma, the only significant difference was a higher S-100B concentration in hypothyroid dogs (P=.003) at 18 months.

CONCLUSIONS

BBB integrity is disrupted in chronic hypothyroidism. Significant increases in CSF concentrations of VEGF and S100-B in hypothyroid dogs indicate dysfunction in both endothelial and glial elements of the BBB.

Short-term effect of recombinant human thyroid-stimulating hormone on thyroid volume and echogenicity in healthy beagles

In humans, administration of recombinant human thyroid stimulating hormone (rhTSH) allows radioactive iodine dose reduction and higher efficacy in the treatment of multinodular goiter and thyroid cancer. A similar effect might be expected in dogs with thyroid carcinoma. However, if rhTSH leads to an increase in thyroid volume, it must be used carefully in dogs with large thyroid tumors to avoid compression of key anatomical structures. The aim of this study was to determine the short-term effect of rhTSH on thyroid volume and echogenicity, measured by ultrasonography, in healthy Beagles. Seven beagles were divided randomly in two groups in a prospective placebo-controlled blinded cross-over study. On day 1, one group received 100 microg of rhTSH intravenously and the other group received placebo. After a wash-out period of 3 weeks, the groups were crossed over. Evaluation of thyroid echogenicity, homogeneity, shape, capsule delineation, and measurement of thyroid length, width, and height were performed by the same observer at baseline, and at 6, 24, and 48h after injection of rhTSH and placebo. There was no significant difference between the effect of rhTSH and placebo on thyroid volume (P = 0.397), echogenicity, homogeneity, or capsule delineation. Time had a significant effect on thyroid volume (P = 0.027). No adverse effects after rhTSH administration were noticed. The effect of rhTSH on thyroid volume in dogs with thyroid carcinoma needs to be assessed.

Thyroid stimulation with recombinant human thyrotropin in healthy cats, cats with non-thyroidal illness and in cats with low serum thyroxin and azotaemia after treatment of hyperthyroidism

This study investigated the recombinant human thyrotropin (rhTSH) stimulation test in healthy cats (group 1), cats with non-thyroidal illness (group 2) and cats with low serum total T(4) (TT(4)) and azotaemia after (131)I treatment (group 3). Serum TT(4) responses and thyroidal pertechnetate uptake after administration of 25 microg rhTSH IV were assessed. Baseline serum TT(4) was significantly lower in group 3 compared with group 1, but not between other group pairs. Serum TT(4) increased significantly in groups 1 and 2 but not in group 3 after rhTSH administration. Post-rhTSH serum TT(4) concentrations differed significantly between groups 1 and 3 and groups 2 and 3, but not between groups 1 and 2. Thyroid/salivary gland uptake ratio (T/S uptake ratio) differed only significantly between groups 1 and 3. Stimulation with rhTSH is valuable to differentiate euthyroidism from iatrogenic hypothyroidism in cats.

Effect of recombinant human thyroid stimulating hormone on serum thyroxin and thyroid scintigraphy in euthyroid cats

This study investigated the thyroidal response to administration of recombinant human thyroid stimulating hormone (rhTSH) by means of serum total thyroxine (TT(4)) concentration and pertechnetate uptake by the thyroid gland in six healthy euthyroid spayed female cats. A pertechnetate scan was performed on day 1 to calculate thyroid/salivary gland (T/S) uptake ratio. On day 3, 25 microg rhTSH was injected intravenously. Six hours later the thyroid scan was repeated as on day 1. Blood was drawn for serum TT(4) measurement prior to injection of rhTSH and performance of the pertechnetate scan. Statistically significant differences in mean serum TT(4) concentration, T/S uptake ratio before and 6h after rhTSH administration and T/S uptake ratio between left and right lobes were noted. We can conclude that 25 microg rhTSH increases pertechnetate uptake in the thyroid glands of cats, this should be taken into account when thyroid scintigraphy after rhTSH administration is interpreted.