Canine serum thyroglobulin autoantibodies in health, hypothyroidism and non-thyroidal illness

Assessment of the likelihood of hypothyroidism in dogs diagnosed with and treated for hypothyroidism at primary care practices: 102 cases (2016-2021)

BACKGROUND

There is a possibility that an incorrect diagnosis of hypothyroidism could be made in euthyroid dogs, and the prevalence of hypothyroidism in the dog population remains unknown.

OBJECTIVES

To retrospectively assess the percentage of dogs diagnosed with, and treated for, hypothyroidism at first opinion practice which are likely to be hypothyroid and require levothyroxine supplementation.

ANIMALS

One hundred two client-owned dogs were included in this study.

MATERIALS AND METHODS

The computerized databases of 7 first opinion practices were searched to identify dogs treated with levothyroxine supplementation. Three European College of Veterinary Internal Medicine-Companian Animals (ECVIM-CA) diplomates independently assigned 1 of 4 clinical assessments to each case as follows: confirmed or likely hypothyroid, hypothyroidism suspected but not confirmed, hypothyroidism considered unlikely, and no reason to suspect hypothyroidism. They commented as to whether or not they thought levothyroxine supplementation was appropriate.

RESULTS

The clinical assessments of "confirmed or likely hypothyroid"; "Hypothyroidism suspected but not confirmed"; "Hypothyroidism considered unlikely"; and "No reason to suspect hypothyroidism" was assigned respectively by Clinician 1 to 38.2%, 5.9%, 3.9%, and 52% of cases, by Clinician 2 to 48%, 22.6%, 22.6%, 6.9% of cases, and by Clinician 3 to 55.9%, 11.8%, 13.7% and 18.6%. Clinician 1, Clinician 2, and Clinician 3 considered levothyroxine supplementation not indicated in 58.8%, 52.9%, and 45.1% of cases, respectively.

CONCLUSION

These results support the concern that hypothyroidism might be overly and incorrectly diagnosed in first opinion practice, and that thyroid function testing should be performed only in those dogs with a high pretest probability of the disease.

2023 AAHA Selected Endocrinopathies of Dogs and Cats Guidelines

Canine and feline endocrinopathies reflect an endocrine gland disease or dysfunction with resulting hormonal abnormali ties that can variably affect the patient's wellbeing, quality of life, and life expectancy. These guidelines provide consensus recommendations for diagnosis and treatment of four canine and feline endocrinopathies commonly encountered in clini cal practice: canine hypothyroidism, canine hypercortisolism (Cushing's syndrome), canine hypoadrenocorticism (Addi son's disease), and feline hyperthyroidism. To aid the general practitioner in navigating these common diseases, a stepwise diagnosis and treatment algorithm and relevant background information is provided for managing each of these diseases. The guidelines also describe, in lesser detail, the diagnosis and treatment of three relatively less common endo crinopathies of cats: feline hyperaldosteronism, feline hypothyroidism, and feline hyperadrenocorticism. Additionally, the guidelines present tips on effective veterinary team utilization and client communication when discussing endocrine cases.

Thyroid hormones in canine pregnancy and lactation

It is believed that thyroid function has a significant effect on fertility and fetal development in mammals. So far, however, only few studies have been published about potential effects of the reproductive cycle stage on thyroid hormone concentrations in dogs. Therefore, over the course of 122 pregnant and non-pregnant cycles in healthy bitches, Thyroid stimulating hormone (TSH), free Thyroxine (fT4), total Thyroxine (tT4) and Progesterone (P4) were measured six times to assess the influence of the cycle stage and pregnancy on hormone concentrations. The aim was to evaluate established reference intervals for the thyroid hormones in a female study population. Of the 122 bitches, 98 became pregnant. Blood samples were collected during estrus, three times in pregnancy, during lactation and after weaning, or at equivalent times during and after estrus in non-pregnant dogs. No differences between pregnant and non-pregnant animals in any of the thyroid hormones were found. Hormone concentrations, however, differed significantly between the six samplings (p < .01). TSH initially declined during pregnancy, then rose again. The mean concentration of all dogs exceeded the overall upper reference limit of 0.70 ng/mL during lactation. Concentrations of tT4 and ft4 increased during the first third of pregnancy and then subsequently declined. The overall reference limits for tT4 were 0.47-3.20 μg/dL, and for fT4 4.86-29.60 pmol/L, but the reference intervals varied between the sampling dates. The observed patterns may reflect that maternal tT4 and fT4 seem to have important effects during early pregnancy, including a pronounced negative feedback effect on TSH. The initial increase and subsequent decline of tT4 and fT4 concentrations during the course of pregnancy is in accordance with findings in humans and may support the development of fetal thyroid function. The observed peak of TSH concentrations during lactation suggests that the demand for thyroid hormones in this phase is largest. Even if the underlying causes and mechanisms of thyroid regulation are not fully understood, the results of this study show relevant changes of hormone concentrations in the course of the sexual cycle and pregnancy. In that regard, cycle stage needs to be considered when assessing thyroid function in bitches.

Understanding the effects of sustained supraphysiologic concentrations of luteinizing hormone in gonadectomized dogs: What we know and what we still need to learn

Removal of the gonads with surgical sterilization results in a loss of negative feedback to the hypothalamus and anterior pituitary. The sustained supraphysiologic luteinizing hormone (LH) concentrations in gonadectomized dogs can significantly alter organ function and even induce neoplastic changes. For example, gonad removal has a profound effect on thyroid function and is reported to be the most significant cause for the development of hypothyroidism in dogs. Thirty percent more gonadectomized dogs develop hypothyroidism compared with intact dogs. Within the canine thyroid, LH receptors are co-localized with thyroid stimulating hormone (TSH) receptors. Continuous LH receptor activation in gonadectomized dogs may interfere TSH receptor function by consuming second messengers involved in G-protein receptor cell signaling, preventing the action of TSH when it binds to its receptor in the thyroid, resulting in hypothyroidism. The incidence of anterior cruciate ligament ruptures is significantly increased following gonad removal independent of breed, sex, weight or body condition. Luteinizing hormone receptors are expressed in the cruciate ligament and continuous LH receptor activation may increase laxity in these ligaments, resulting in joint instability. Both male and female gonadectomized dogs are at a significantly increased risk for lymphoma and hemangiosarcoma. Luteinizing hormone receptors are also abundant in these tissues. Research in four canine hemangiosarcoma cell lines found that LH receptor activation induces cell proliferation. In addition, research in three canine T-cell lymphoma cell lines found that LH receptor activation induces cell proliferation, adhesion, and invasion as well as increases LH receptor expression. Research is needed to determine if LH reducing strategies using gonadotropin releasing hormone agonists will increase remission times in gonadectomized dogs with LH receptor-positive tumors. In conclusion, among the non-reproductive functions of gonads, suppression of LH secretion and resulting LH receptor overexpression appear necessary in maintaining endocrine, musculoskeletal, and anti-neoplastic health.

Laboratory indicators of hypothyroidism and TgAA-positivity in the Eurasian dog breed

BACKGROUND

Hereditary hypothyroidism represents a concern for dog breeders; thus, surveillance programs have been established for several dog breeds.

METHODS

Thyroid profiles (total thyroxine (TT4), thyrotropin (thyroid stimulating hormone (TSH)), and thyroglobulin autoantibodies (TgAA)) collected as part of a breed surveillance program in Eurasians (2009-2017) were retrospectively analyzed. The study included data from 1,501 Eurasians from a German breeding club. Classification was exclusively based on laboratory data. Hypothyroidism was defined as a combined decrease in TT4 and increase in TSH in serum and was classified as TgAA-positive and TgAA-negative hypothyroidism. Thyroglobulin autoantibodies (TgAA) independent of the concentrations of TT4 and TSH were determined. The overall prevalence of hypothyroidism, TgAA-positive hypothyroidism, TgAA-negative hypothyroidism and TgAA-positivity was assessed when the dogs entered the program. Follow-up laboratory data was available for 324 dogs without hypothyroidism on initial examination.

RESULTS

The initial screening was performed at a median age of 18 months (interquartile range (IQR): 15-29). The overall prevalence of hypothyroidism was 3.9% (n = 58; 95% CI: 2.9-4.8%) and the prevalence of a positive TgAA status was 7.9% (n = 118; 95% CI: 6.6-9.3%). The prevalence of TgAA-positive and TgAA-negative hypothyroidism was 1.7% (n = 26; 95% CI: 1.1-2.4%) and 2.1% (n = 32; 95% CI: 1.4-2.9%), respectively. 22.0% of dogs with positive TgAA status (26/118) were already hypothyroid on initial examination. Overall, 42.5% (17/40) of TgAA-positive dogs on initial examination developed hypothyroidism on follow-up.

CONCLUSION

The results of this study demonstrate that the Eurasian dog breed exhibits a relevant risk for hypothyroidism and presence of TgAA. The predictive value of TgAA for hypothyroidism or developing hypothyroidism was high in this breed. Further investigations with longitudinal studies in individual dogs are warranted.

A scoping review of autoantibodies as biomarkers for canine autoimmune disease

Background

Autoantibody biomarkers are valuable tools used to diagnose and manage autoimmune diseases in dogs. However, prior publications have raised concerns over a lack of standardization and sufficient validation for the use of biomarkers in veterinary medicine.

Objectives

Systematically compile primary research on autoantibody biomarkers for autoimmune disease in dogs, summarize their methodological features, and evaluate their quality; synthesize data supporting their use into a resource for veterinarians and researchers.

Animals

Not used.

Methods

Five indices were searched to identify studies for evaluation: PubMed, CAB Abstracts, Web of Science, Agricola, and SCOPUS. Two independent reviewers (AET and ELC) screened titles and abstracts for exclusion criteria followed by full‐text review of remaining articles. Relevant studies were classified based on study objectives (biomarker, epitope, technique). Data on study characteristics and outcomes were synthesized in independent data tables for each classification.

Results

Ninety‐two studies qualified for final analysis (n = 49 biomarker, n = 9 epitope, and n = 34 technique studies). A high degree of heterogeneity in study characteristics and outcomes reporting was observed. Opportunities to strengthen future studies could include: (1) routine use of negative controls, (2) power analyses to inform sample sizes, (3) statistical analyses when appropriate, and (4) multiple detection techniques to confirm results.

Conclusions

These findings provide a resource that will allow veterinary clinicians to efficiently evaluate the evidence supporting the use of autoantibody biomarkers, along with the varied methodological approaches used in their development.

Possible Relationship between Long-Term Adverse Health Effects of Gonad-Removing Surgical Sterilization and Luteinizing Hormone in Dogs

Spaying and neutering dogs is commonly used to prevent the birth of unwanted animals and eliminate the risk of reproductive diseases. However, removal of the gonads prevents the feedback of estrogen and testosterone on the pituitary and hypothalamus. As a result, luteinizing hormone (LH) is continuously elevated at supraphysiologic concentrations. Although the main role of LH is for reproductive function (e.g., ovulation), there are LH receptors present in several normal tissues including the thyroid and adrenal glands, gastrointestinal tract, cranial cruciate ligament and round ligament, and lymphocytes. In addition, there are LH receptors present in several neoplastic tissues (e.g., lymphoma, hemangiosarcoma, mastocytoma, transitional cell carcinoma, and osteosarcoma). The role of LH receptors in non-reproductive normal and neoplastic tissues is not known but may stimulate nitric oxide release and induce cell division. The precise etiology of the increased incidence of several non-reproductive long-term health complications following spaying and neutering is not known but may be related to LH receptor activation in these non-reproductive target tissues. How these effects may be mediated is described in this review.

A Review of the Impact of Neuter Status on Expression of Inherited Conditions in Dogs

Gonadectomy is an important reproductive management tool employed in many countries, and is highly prevalent in the US with an estimated 85% of dogs being neutered. Despite the societal benefits in pet population control, negative associations between neuter status, and health conditions have been reported in recent years. Most particularly observed are the consequences of early age neutering. Knowing that different physiological systems rely upon gonadal steroids during development and physiological maintenance, studies have been undertaken to assess the impact of neuter status on multiple body and organ systems. For some inherited conditions, neutering is associated with an increased risk of expression. Neutering has also been associated with altered metabolism and a predisposition for weight gain in dogs, which may confound the detected risk association between neutering and disease expression. This review summarizes the effects of neutering on cancer, orthopedic, and immune disorders in the dog and also explores the potentially exacerbating factor of body weight.

A longitudinal study of autoantibodies against cytochrome P450 side-chain cleavage enzyme in dogs (Canis lupus familiaris) affected with hypoadrenocorticism (Addison's disease)

Autoantibodies directed against the P450 side chain cleavage enzyme (P450scc) have been recently described in dogs affected with hypoadrenocorticism, consistent with an immune-mediated pathogenesis of this endocrinopathy. In human autoimmune Addison's disease, autoantibodies may have a predictive value, being detectable before clinical signs developing, and have been shown to persist for a period of time after diagnosis. Furthermore, an autoantibody positive status post-diagnosis has been associated with successful remission of Addison's disease following B-cell depletion, suggesting active immunopathology in these cases. The current study was designed to investigate changes in serum P450scc autoantibody status over time in dogs diagnosed with spontaneous hypoadrenocorticism. P450scc autoantibodies were measured using a species-specific radioimmunoprecipitation assay in an initial cohort of 213 dogs, indicating a prevalence of 24%. Thirty two of these dogs had repeat samples (n = 80 in total) available for analysis. Five dogs were consistently P450scc autoantibody positive in all samples, for up to 425 days following first sampling. Three dogs were initially autoantibody positive, then became seronegative at later time points. One dog, a 1 year old female entire standard poodle, was initially negative for P450scc autoantibodies, but seroconverted 18 months after diagnosis. The remaining 23 dogs with multiple samples available were consistently P450scc autoantibody negative. Persistence was not associated with sex (p = .673). This study demonstrates persistence of P450scc autoantibodies in a subset of dogs affected with hypoadrenocorticism and seroconversion over one year post-diagnosis. P450scc autoantibody reactivity in human autoimmune Addison's disease has been associated with sex, with females having a higher prevalence, possibly due to P450scc expression in the ovary acting as an additional source of antigenic stimulation. However, there was no sex difference in autoantibody persistence in the dogs affected with hypoadrenocorticism. Autontibody persistence in dogs with hypoadrenocorticism might represent persistent pathology, due to residual antigenic stimulation and autoimmune inflammation in the adrenal gland.

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.

Kastration der Hündin – neue und alte Erkenntnisse zu Vor- und Nachteilen

Die Beratung von Hundehaltern bezüglich der Vorteile und Nachteile sowie des optimalen Zeitpunktes der Kastration einer Hündin ist komplex und sollte sich auf verlässliche Daten aus der Wissenschaft stützen sowie individuelle Belange berücksichtigen. Bei genauerer Betrachtung der aktuellen Publikationen zu diesem Thema fällt auf, dass einige lange für robust gehaltene Informationen etwas angepasst oder aktualisiert werden müssen. Ein offensichtlicher Vorteil der elektiven Kastration ist, dass Erkrankungen der Ovarien und sexualsteroidabhängige Erkrankungen wie Metropathien nicht auftreten. Weiterhin ist ein gewisser protektiver Effekt einer frühzeitigen Kastration auf die Entstehung von Mammatumoren anzunehmen, wenngleich dafür derzeit eine schwache wissenschaftliche Evidenz besteht und der Effekt vermutlich geringer ausfällt, als in einigen älteren Publikationen angegeben wurde. Die Kastration hat jedoch auch Nachteile. Als häufigste negative Folge wird seit Jahrzehnten die Harninkontinenz beschrieben. Aussagen zur Inzidenz sowie zu weiteren Einflussfaktoren, wie Kastrationszeitpunkt in Bezug zur Pubertät, sind jedoch uneinheitlich. Aktuell werden vor allem das gehäufte Auftreten verschiedener Tumorerkrankungen, die nicht direkt mit dem Reproduktionstrakt in Verbindung stehen, sowie ein höheres Risiko für Erkrankungen des Bewegungsapparats bei kastrierten Tieren diskutiert. Weitere Einflussfaktoren wie der Ernährungszustand des Hundes, Alter und/oder Haltung wurden jedoch häufig nicht erfasst. Die Datenlage zur Auswirkung der Kastration auf den Stoffwechsel und das Immunsystem der Hündin ist derzeit ungenügend. Wünscht der Tierbesitzer eine Kastration, bedarf es in jedem Fall einer eingehenden Beratung, die individuelle, rasse- und haltungsbezogene Aspekte einschließt. Derzeit ist eine Kastration am ehesten zwischen der ersten und zweiten Läufigkeit zu empfehlen, da ein gewisser protektiver Effekt auf die Entstehung von Mammatumoren anzunehmen ist und das Risiko unerwünschter Nebenwirkungen nach heutigem Wissensstand moderat ausfällt.

Altered Serum Thyrotropin Concentrations in Dogs with Primary Hypoadrenocorticism before and during Treatment

Background

Thyrotropin (TSH) can be increased in humans with primary hypoadrenocorticism (HA) before glucocorticoid treatment. Increase in TSH is a typical finding of primary hypothyroidism and both diseases can occur concurrently (Schmidt's syndrome); therefore, care must be taken in assessing thyroid function in untreated human patients with HA.

Objective

Evaluate whether alterations in cTSH can be observed in dogs with HA in absence of primary hypothyroidism.

Animals

Thirty dogs with newly diagnosed HA, and 30 dogs in which HA was suspected but excluded based on a normal ACTH stimulation test (controls) were prospectively enrolled.

Methods

cTSH and T4 concentrations were determined in all dogs and at selected time points during treatment (prednisolone, fludrocortisone, or DOCP) in dogs with HA.

Results

cTSH concentrations ranged from 0.01 to 2.6 ng/mL (median 0.29) and were increased in 11/30 dogs with HA; values in controls were all within the reference interval (range: 0.01–0.2 ng/dL; median 0.06). There was no difference in T4 between dogs with increased cTSH (T4 range 1.0‐2.1; median 1.3 μg/dL) compared to those with normal cTSH (T4 range 0.5‐3.4, median 1.4 μg/dL; P=0.69) and controls (T4 range 0.3‐3.8, median 1.8 μg/dL; P=0.35). After starting treatment, cTSH normalized after 2–4 weeks in 9 dogs and after 3 and 4 months in 2 without thyroxine supplementation.

Conclusions and Clinical Relevance

Evaluation of thyroid function in untreated dogs with HA can lead to misdiagnosis of hypothyroidism; treatment with glucocorticoids for up to 4 months can be necessary to normalize cTSH.

Autoantibodies against Cytochrome P450 Side-Chain Cleavage Enzyme in Dogs (Canis lupus familiaris) Affected with Hypoadrenocorticism (Addison's Disease)

Canine hypoadrenocorticism likely arises from immune-mediated destruction of adrenocortical tissue, leading to glucocorticoid and mineralocorticoid deficiency. In humans with autoimmune Addison's disease (AAD) or autoimmune polyendocrine syndrome (APS), circulating autoantibodies have been demonstrated against enzymes associated with adrenal steroid synthesis. The current study investigates autoantibodies against steroid synthesis enzymes in dogs with spontaneous hypoadrenocorticism. Coding regions of canine CYP21A2 (21-hydroxylase; 21-OH), CYP17A1 (17-hydroxylase; 17-OH), CYP11A1 (P450 side-chain cleavage enzyme; P450scc) and HSD3B2 (3β hydroxysteroid dehydrogenase; 3βHSD) were amplified, cloned and expressed as 35S-methionine radiolabelled recombinant protein. In a pilot study, serum samples from 20 dogs with hypoadrenocorticism and four unaffected control dogs were screened by radio-immunoprecipitation assay. There was no evidence of reactivity against 21-OH, 17-OH or 3βHSD, but five dogs with hypoadrenocorticism showed immunoreactivity to P450scc compared with controls. Serum samples were subsequently obtained from 213 dogs diagnosed with hypoadrenocorticism and 110 dogs from a hospital control population. Thirty control dogs were randomly selected to establish a threshold for antibody positivity (mean + 3 × standard deviation). Dogs with hypoadrenocorticism were more likely to be P450scc autoantibody positive than hospital controls (24% vs. 1.2%, respectively; p = 0.0016). Sex was significantly associated with the presence of P450scc autoantibodies in the case population, with 30% of females testing positive compared with 17% of males (p = 0.037). Significant associations with breed (p = 0.015) and DLA-type (DQA1*006:01 allele; p = 0.017) were also found. This cross-sectional study indicates that P450scc autoantibodies are present in a proportion of dogs affected with hypoadrenocorticism.

Free thyroxine concentrations by equilibrium dialysis and chemiluminescent immunoassays in 13 hypothyroid dogs positive for thyroglobulin antibody

Objective

To determine if concentrations of free thyroxine (FT4) measured by semi‐automated chemiluminescent immunoassay (CLIA) correspond to FT4 determined by equilibrium dialysis (ED) in hypothyroid dogs positive for thyroglobulin antibody (TGA).

Animals

Thirteen TGA‐positive dogs classified as hypothyroid based on subnormal FT4 concentrations by ED.

Methods

Qualitative assessment of canine TGA was performed using an enzyme‐linked immunosorbent assay. Serum total thyroxine and total triiodothyronine concentrations were measured by radioimmunoassay. Serum FT4 concentration was determined by ED, and also by semi‐automated CLIA for human FT4 (FT4h) and veterinary FT4 (FT4v). Canine thyroid stimulating hormone concentration was measured by semi‐automated CLIA.

Results

Each dog's comprehensive thyroid profile supported a diagnosis of hypothyroidism. For detection of hypothyroidism, sensitivities of CLIA for FT4h and FT4v were 62% (95% CI, 32–85%) and 75% (95% CI, 36–96%), respectively, compared to FT4 by ED. Five of 13 (38%) dogs had FT4h and 2 of 8 (25%) dogs had FT4v concentrations by CLIA that were increased or within the reference range. Percentage of false‐negative test results for FT4 by CLIA compared to ED was significantly (P < .0001 for FT4h and P < .001for FT4v) higher than the hypothesized false‐negative rate of 0%.

Conclusions and Clinical Importance

Caution should be exercised in screening dogs for hypothyroidism using FT4 measured by CLIA alone. Some (25–38%) TGA‐positive hypothyroid dogs had FT4 concentrations determined by CLIA that did not support a diagnosis of hypothyroidism.

Canine hypothyroidism: a review of aetiology and diagnosis

Hypothyroidism is recognised as an important endocrine disorder of dogs, and a frequent differential for numerous presenting complaints. Its diagnosis has never been straight forward as results suggestive of hypothyroidism can occur for a variety of reasons in dogs with normal thyroid function (euthyroid). As a consequence, the accurate investigation of hypothyroidism has been hindered by the potential inclusion of a number of cases not truly hypothyroid. In recent years, the development of newer diagnostic tests, e.g. free thyroxine, canine thyroid stimulating hormone, thyroglobulin autoantibodies, has significantly improved our ability to reliably differentiate hypothyroidism from other clinically similar disorders. This has led to a marked increase in our knowledge of the phenotypic, genotypic and aetiological aspects of this disorder in dogs.

Increased genetic risk or protection for canine autoimmune lymphocytic thyroiditis in Giant Schnauzers depends on DLA class II genotype

Dogs represent an excellent comparative model for autoimmune thyroiditis as several dog breeds develop canine lymphocytic thyroiditis (CLT), which is clinically similar to Hashimoto's thyroiditis in human. We obtained evidence that dog leukocyte antigen (DLA) class II genotype function as either genetic risk factor that predisposes for CLT or as protective factor against the disease. Genetic diversity at their DLA-DRB1, -DQA1, and -DQB1 loci were defined and potential association to major histocompatibility complex II haplotypes and alleles was analyzed. Giant Schnauzers carrying the DLA-DRB1*01201/DQA1*00101/DQB1*00201 haplotype showed an increased risk (odds ratio of 6.5) for developing CLT. The same risk haplotype has, to date, been observed in three different breeds affected by this disease, Giant Schnauzer, Dobermann, and Labrador Retriever, indicating that it is a common genetic risk factor in a variety of breeds affected by this disease. Importantly, protection for development of the disease was found in dogs carrying the DLA-DRB1*01301/DQA1*00301/DQB1*00501 haplotype (odds ratio of 0.3).

Quantitative thyroid scintigraphy in greyhounds suspected of primary hypothyroidism

The existence of hypothyroidism in greyhounds remains controversial and its investigation is complicated by the low circulating thyroid hormone concentrations typically found in healthy dogs of this breed. Quantitative measurement of thyroidal technetium-99m pertechnetate ((99m)TcO4-) uptake is known to be useful in assessing thyroid function in other breeds. The aim of this study was to evaluate thyroid scintigraphy as a method of assessing thyroid function in greyhounds suspected of primary hypothyroidism. Twenty greyhounds (eight females, 12 males) were studied. Thirteen had bald thigh syndrome and seven poor performance and low total T4. Total T4 concentrations were decreased in 18 (90%), and free T4 in two (10%) dogs. All canine thyroid stimulating hormone concentrations were within the reference interval. Thyroidal (99m)TcO4- uptake values (mean +/- SD, 0.76 +/- 0.26%) were within the reference limits published for euthyroid dogs (0.39-1.86%) making hypothyroidism highly unlikely. There were no significant differences (P < 0.05) when comparing data between dogs with bald thigh syndrome (13 dogs) and the remaining dogs (seven dogs). Seventeen (85%) dogs had higher uptake in the left thyroid gland than in the right that might reflect an anatomic feature of the greyhound breed. Calculation of percent thyroidal uptake of (99m)TcO4- is more accurate than thyroid: salivary gland ratios because of high variability in salivary gland uptake. Percent thyroidal uptake of (99m)TcO4- should be used when assessing thyroid function scintigraphically in the greyhound breed.

Comparative dermatology—canine endocrine dermatoses

Endocrine diseases in the dog commonly manifest with dermatological lesions. Hypothyroidism is the most common endocrinopathy and usually presents with alopecia in areas of wear, seborrhea, and recurrent infections. Common clinical signs associated with hyperadrenocorticism include polyuria, polydipsia, and polyphagia. The most common dermatological manifestation of hyperadrenocorticism is bilaterally symmetrical alopecia sparing the head and distal extremities. Pyoderma is a common finding associated with immunosuppression. Less commonly, calcinosus cutis may occur. Sex hormone excess, primarily hyperestrogenism and hyperandrogenism, may also be associated with dermatological signs. Usually, dogs are intact, and the excess production is due to testicular or ovarian neoplasia.

Association of canine hypothyroidism with a common major histocompatibility complex DLA class II allele

Dogs exhibit a range of immune-mediated conditions including a lymphocytic thyroiditis which has many similarities to Hashimoto's thyroiditis in man. We have recently reported an association in Doberman Pinschers between canine hypothyroidism and a rare DLA class II haplotype that contains the DLA-DQA1*00101 allele. We now report a further series of 173 hypothyroid dogs in a range of breeds where a significant association with DLA-DQA1*00101 is shown.

Lymphocytic-plasmacytic thyroiditis and glomerulonephritis in a boxer

An 18-month-old boxer was presented for investigation of profound lethargy, and primary hypothyroidism was diagnosed. A strong antithyroglobulin antibody titre was also present, indicating lymphocytic (immune-mediated) thyroiditis as the cause of hypothyroidism. A concurrent protein-losing glomerulonephropathy was also detected, although the aetiology could not be determined at initial presentation. Thyroid replacement and dietary therapy were prescribed. The dog improved clinically for approximately 12 months when it was re-presented with poorly controlled hypothyroidism and renal failure. Postmortem examination confirmed the presence of lymphocytic-plasmacytic thyroiditis, in conjunction with membranoproliferative glomerulonephritis and renal failure.

Association of hypothyroid disease in Doberman Pinscher dogs with a rare major histocompatibility complex DLA class II haplotype

Canine hypothyroid disease is similar to Hashimoto's disease in humans, which has been shown to be associated with human major histocompatibility complex (MHC) genes. We have collected 27 Doberman Pinschers affected with primary hypothyroid disease and compared their MHC class II haplotypes with 129 unaffected Doberman Pinschers. Three dog-leucocyte antigen (DLA) genes, DLA-DRB1, DQA1 and DQB1, were characterized by sequence-based typing and assigned to haplotypes for each dog. One rare haplotype was found at an increased frequency in the affected dogs compared to the unaffected dogs (Odds ratio = 2.43, P < 0.02). This haplotype has only been found in Doberman Pinschers and Labradors to date.

Tryptic peptides of canine thyroglobulin reactive with sera of patients with canine hypothyroidism caused by autoimmune thyroiditis

Canine thyroglobulin (cTg) was treated with trypsin at a ratio of trypsin to cTg of 1:100 (w/w). Tryptic peptides of cTg were analysed by Western immunoblotting for their reactivity to serum thyroglobulin autoantibodies (TgAA) from patients with TgAA-positive hypothyroidism and normal individuals. The sera of patients with TgAA-positive hypothyroidism reacted with several peptides: 43, 32.5 and 31 kDa; the sera of normal individuals did not bind these tryptic peptides. Some of the TgAA-positive sera of patients reacted with 25 kDa peptide in addition to three tryptic peptides above. This experiment was the first report about antigenic epitopes of cTg. These small tryptic peptides recognized by TgAA may be related with the induction of TgAA and may be useful as markers for autoimmune thyroid diseases in dog.

Prevalence of thyroglobulin autoantibodies detected by enzyme-linked immunosorbent assay of canine serum in hypothyroid, obese and healthy dogs in Japan

Thyroglobulin autoantibodies (TgAA) were detected in sera of hypothyroid (n=19), obese (n=28) and clinically healthy dogs (n=52) using a commercially available immunoassay kit. TgAA-positive results occurred in 10 of 19 hypothyroid, 1 of 28 obese and 1 of 52 clinically healthy dogs. The clinically healthy TgAA-positive dog had additional evidence of hypothyroidism supported by low total T(4), low free T(4) and high canine TSH. Among the breeds, Golden Retriever had the highest frequency of hypothyroid (9/19) and TgAA-positive hypothyroid dogs (6/10). This study was the first survey about the prevalence of canine TgAA in Japan and could be a useful reference for clinicians.

Evaluation of thyroid function in obese dogs and in dogs undergoing a weight loss protocol

Obesity and weight loss have been shown to alter thyroid hormone homeostasis in humans. In dogs, obesity is the most common nutritional problem encountered and weight loss is the cornerstone of its treatment. Therefore, it is important to clarify how obesity and weight loss can affect thyroid function test results in that species. The objectives of this study were to compare thyroid function in obese dogs and in lean dogs and to explore the effects of caloric restriction and weight loss on thyroid hormone serum concentrations in obese dogs. In the first experiment, 12 healthy lean beagles and 12 obese beagles were compared. Thyroid function was evaluated by measuring serum concentrations of total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), thyrotropin (TSH), and reverse triiodothyronine (rT3) as well as a TSH stimulation test using 75 microg i.v. of recombinant human TSH. In the second experiment, eight obese beagles were fed an energy-restricted diet [average 63% maintenance energy requirement (MER)] until optimal weight was obtained. Blood samples for determination of TT4, FT4, TT3, TSH and rT3, were taken at the start and then weekly during weight loss. Only TT3 and TT4 serum concentrations were significantly higher in obese dogs as compared to lean dogs. In the second experiment, weight loss resulted in a significant decrease in TT3 and TSH serum concentrations. Thus obesity and energy restriction significantly alter thyroid homeostasis in dogs, but the observed changes are unlikely to affect interpretation of thyroid function test results in clinics.

Determination of autoantibodies to thyroglobulin, thyroxine and triiodothyronine in canine serum

Enzyme immunoassays (EIAs) for the determination of autoanti-bodies (AA) to thyroid antigens in canine serum were developed. Streptavidin (SA) was immobilized as capture molecule on microtitreplates (MTP). Thyroglobulin (Tg) purified from canine thyroids and the thyroid hormones thyroxine and triiodothyronine (T3 and T4) were conjugated to biotin labelling reagents and attached to the MTP over the SA-biotin bridge. Bound AA were detected with anti-dog-immunoglobulin G (IgG) labelled with horseradish peroxidase. Serum samples from dogs which were allotted to four groups were analysed: A (n = 31), biochemical evidence of hypothyroidism; B (n = 76), clinical signs of hypothyroidism; C (n = 47), euthyroid with non-thyroidal disease; D (n = 186), clinically healthy. The validity of the assays was tested with two different methods. After thiophilic absorption chromatography of positive sera, a positive reaction in the EIA was only detected in those fractions which coeluted with the canine IgG standard. Furthermore, the positive reaction was blocked by the addition of the corresponding antigen. In 55% of the hypothyroid dogs AA to Tg and/or T3 and T4, respectively, were found (up to a titre of 1 : 1600). In group B 34% of the dogs were diagnosed positive, but the titre was lower (up to 1 : 400). In the groups C and D the number of dogs with AA and their titre was significantly lower. Two different methods for distinguishing positive and negative test results were compared in order to increase the specificity of the tests without decreasing the sensitivity. The EIAs are precise and based on high agreement with previous reported assays able to discriminate dogs with thyroiditis from healthy ones. These assays represent a good alternative to the isotope assays generally used for the analysis of AA to T4 and T3.

Anti-insulin antibodies in dogs with naturally occurring diabetes mellitus

The presence of anti-insulin antibodies was determined by ELISA in serum samples from 30 diabetic dogs receiving bovine insulin therapy and 30 normoglycaemic dogs. Twenty of the diabetic dogs had significant reactivity to both bovine (heterologous) and porcine (homologous) insulin compared to control dogs. In contrast there was no significant difference between the two populations in reactivity to canine distemper virus (CDV) or canine thyroglobulin. The high degree of correlation between anti-bovine insulin and anti-porcine insulin antibodies suggested cross-reactivity which was confirmed by performing a competition ELISA, with antibody binding to bovine insulin inhibited by pre-incubating serum with porcine insulin. The insulin B-chain, rather than the A-chain was the most reactive component of the insulin molecule although in some cases, diabetics with antibody reactivity to whole insulin protein showed minimal reactivity to the individual subunits. The data suggest that treatment of diabetic dogs with bovine insulin can lead to anti-insulin antibody production. These antibodies cross-react with homologous insulin and recognise conformational as well as linear epitopes.

Recognition Pattern of Thyroglobulin Autoantibody from Hypothyroid Dogs to Tryptic Peptides of Canine Thyroglobulin

Circulating thyroglobulin autoantibody (TgAA) was analyzed using the Western immunoblot for determination of the dominant epitopes recognized by TgAA on tryptic peptides of canine thyroglobulin (cTg) in hypothyroid dogs. TgAA was measured in hypothyroid dogs, non-hypothyroid dogs with skin diseases and clinically normal dogs. Five of the 7 hypothyroid dogs, 1 of the 8 dogs with skin diseases and 1 of the 4 normal dogs were positive for TgAA. Four of the 5 TgAA-positive hypothyroid dogs were Golden Retrievers, and 3 of them showed high antibody titers. The sera of TgAA positive-dogs reacted to several peptides, and their patterns varied from sample to sample. Sera from 3 dogs with high titers of TgAA reacted broadly to high molecular weight peptides ranging from 45 to 90 kDa. These Western immunoblot patterns of the sera were disappeared after pretreatment with sufficient amount of intact cTg. All serum samples of both TgAA positive dogs and negative controls reacted to low molecular weight peptides ranging from 15 to 20 kDa. These immunoblot patterns of the sera were not disappeared even after pretreatment with sufficient amount of intact cTg. These findings show the possibility that the epitopes recognized by TgAA depend upon individual dogs with hypothyroidism and these autoantibodies recognize conformational epitopes on the cTg molecule.

Diagnosis of canine hypothyroidism. Perspectives from a testing laboratory

The most common sample received by our endocrine testing laboratory is submitted for the diagnosis of hypothyroidism in a dog. The current tests most frequently employed in our laboratory for thyroid evaluation in dogs are total T4, free T4 by dialysis, and canine TSH measurement. Each test has strengths and weaknesses and suffers from the possibility of both false positive and false negative results. This article provides a working description of each test and an approach to interpretation of results. Other tests that are less commonly used are also discussed. Examples of interpretation of test results in individual hypothyroid-suspect dogs are presented for illustration.

Lymphocytic thyroiditis

Lymphocytic thyroiditis is a common canine condition that can lead to functional hypothyroidism. It is associated with more than 50% of cases of canine hypothyroidism. Evidence in human beings and experimental situations suggests that it is a disease of defective immunoregulation, but specific investigation of the molecular pathogenesis of the naturally occurring disease in dogs has not yet been carried out. The condition is heritable in those breeds that have been studied, and progression to hypothyroidism, if it occurs, can be slow. Factors that influence the progression from subclinical thyroiditis to hypothyroidism in dogs are still to be identified, but excessive iodine intake is an important factor in other species.

Epidemiological, clinical, haematological and biochemical characteristics of canine hypothyroidism

Hypothyroidism was diagnosed in 50 dogs and excluded in 86 dogs suspected of hypothyroidism, on the basis of the results of bovine thyrotropin response tests. Breed, pedigree, sex or neutering status did not significantly influence the likelihood of the dogs being hypothyroid. The hypothyroid dogs were significantly older than the non-hypothyroid dogs referred to the University of Glasgow during the same period. However, when dogs under two years of age were excluded from the statistical analyses there was no significant difference in age between the two groups. The most common clinical characteristics associated with hypothyroidism were metabolic signs (84 per cent of cases), particularly lethargy (76 per cent), obesity or weight gain (44 per cent), and exercise intolerance (24 per cent); and dermatological abnormalities (80 per cent), including alopecia (56 per cent), poor coat quality (30 per cent) and hyperpigmentation (20 per cent). When compared with the laboratory reference limits the most common biochemical and haematological abnormalities were increased concentrations of triglycerides (88 per cent), cholesterol (78 per cent), glucose (49 per cent), and fructosamine (43 per cent), and increased activities of creatine kinase (35 per cent), and decreased concentrations of inorganic phosphate (63 per cent), and a low red blood cell count (40 per cent). When compared with reference limits derived from the euthyroid dogs the most common abnormalities were increased concentrations of gamma-glutamyltransferase (21 per cent), cholesterol (18 per cent), and aspartate aminotransferase (15 per cent) and a decreased red blood cell count (29 per cent), and decreased neutrophils (18 per cent) and decreased activity of creatine kinase (15 per cent). Assessment of cholesterol, creatine kinase, aspartate aminotransferase, gamma-glutamyltransferase, and red blood cell and neutrophil counts may be particularly useful in distinguishing hypothyroid dogs from euthyroid animals with similar clinical signs.