Thyroid Disorders in the Geriatric Patient

Assessment of Sex, Age, and Metabolism Relationships to Serum Thyroid Concentrations in Retired Alaskan Husky Sled Dogs

Sled dogs are purpose-bred dogs selected for endurance work. Prior studies in racing dogs showed that serum thyroid parameters (total T4, free T4, and T3) are lower than the reference range in approximately 25% of dogs. Whether this is related to training, breeding, or body condition remains unclear. We hypothesized that retired sled dogs of normal body condition (9–13 years old) would have predominantly normal serum thyroid parameters and that serum thyroid status would be correlated to energy consumption based on metabolic body weight. Eighty-six sled dogs who were deemed healthy on physical exam, not on confounding medications, and without a prior diagnosis of hypothyroidism were included. All dogs' mean body condition scores were 5.1 ± 0.4 and body weight 24.5 ± 4.2 kg at fasting blood collection with stable dietary intake for 3 months before sampling. The total T4, free T4, and T3 serum concentrations were 23.4 ± 9.1 nmol/L, 9.53 ± 4.3 pmol/L, and 0.93 ± 0.39 nmol/L, respectively, with 38% lower than the reference range for total T4, 45% for free T4, and 37% for T3. All dogs were negative for thyroglobulin antibody, and TSH results were within normal ranges. Pearson's correlates based on kilocalories consumed on a metabolic body weight basis for total T4 (R = 0.14), free T4 (R = 0.01) and T3 (R = 0.23) showed poor correlation. No differences were observed between thyroid hormones and age, breed, or sex. Inactive, retired sled dogs can be misdiagnosed with hypothyroidism; therefore, our data suggests that misdiagnosis of hypothyroidism can occur and that the racing Alaskan sled dog has a unique reference range that should be considered when assessing serum thyroid status.

Screening for dilated cardiomyopathy in dogs

BACKGROUND

Dilated cardiomyopathy (DCM) is the most common cardiac disease in large breed dogs. The disease can start with arrhythmias or with systolic dysfunction of the myocardium.

OBJECTIVE

To describe screening methods for DCM in various breeds and provide a new, modified staging system.

RECOMMENDATIONS

Screening for occult DCM should start at three years of age and use Holter monitoring in Boxers and Dobermans and might be useful also in other breeds. Single ventricular premature complexes (VPCs) can be detected in many healthy dogs, but healthy animals typically have <50 VPCs in 24 h and demonstrate minimal complexity most often occurring only as single ectopic beats. In general, >100 VPCs in 24 h was recommended as the cut-off value for establishing a diagnosis of DCM. However, there are breed-specific recommendations related to Holter recording diagnosis of DCM in Dobermans and Boxers. Yearly screening over the life of a dog is recommended, as a one-time screening is not sufficient to rule out the future development of DCM. Several echocardiographic methods such as M-mode derived measurements, the measurement of the left ventricular (LV) volume by Simpson's method of discs (SMOD), and E-point to septal separation (EPSS) are recommended for screening purposes. The value of additional tests such as cardiac biomarkers (troponin I and N-terminal pro-B-type natriuretic peptide) as well as a 5-min resting electrocardiogram (ECG) or newer echocardiographic methods such as strain measurements is discussed.

CONCLUSION

This review suggests some guidelines for screening for DCM in various breeds.

European Society of Veterinary Cardiology screening guidelines for dilated cardiomyopathy in Doberman Pinschers

BACKGROUND

Dilated cardiomyopathy (DCM) is the most common cardiac disease in large breed dogs and is inherited in Doberman Pinschers with a high prevalence (58%).

OBJECTIVE

The European Society for Veterinary Cardiology convened a task force to formulate screening guidelines for DCM in Dobermans.

RECOMMENDATIONS

Screening for occult DCM in Dobermans should start at three years of age and use both Holter monitoring and echocardiography. Yearly screening over the life of the dog is recommended, as a one-time screening is not sufficient to rule out future development of DCM. The preferred echocardiographic method is the measurement of the left ventricular volume by Simpson's method of discs (SMOD). Less than 50 single ventricular premature complexes (VPCs) in 24 h are considered to be normal in Dobermans, although detection of any number of VPCs is cause for concern. Greater than 300 VPCs in 24 h or two subsequent recordings within a year showing between 50 and 300 VPCs in 24 h is considered diagnostic of occult DCM in Dobermans regardless of the concurrent echocardiographic findings. The guidelines also provide recommendations concerning ancillary tests, that are not included in the standard screening protocol, but which may have some utility when recommended tests are not available or financially untenable on an annual basis. These tests include assay of cardiac biomarkers (Troponin I and N-Terminal pro-B-type Natriuretic Peptide) as well as a 5-min resting electrocardiogram (ECG).

CONCLUSION

The current guidelines should help to establish an early diagnosis of DCM in Dobermans.

A critical review of food-associated factors proposed in the etiology of feline hyperthyroidism

Since the first description of feline hyperthyroidism (HT) in 1979, several studies have been undertaken to define the etiology of the disease. Epidemiologic studies, after investigating non-food- and food-associated factors, suggest a multifactorial etiology. However, in the absence of prospective cohort studies that can confirm a cause-and-effect relationship between HT and associated risk factors, no causative factor for HT has been identified to date. Feline HT resembles toxic nodular goiter in humans, with autonomously functioning upregulated iodide uptake systems. Contribution of the diet to HT development remains controversial. The purpose of this paper is to review critically the reported food-associated risk factors for HT.

The role of hypothyroidism in the etiology and progression of dilated cardiomyopathy in Doberman Pinschers

BACKGROUND

Hypothyroidism and dilated cardiomyopathy (DCM) are both common diseases in Doberman Pinschers. A possible influence of hypothyroidism on the etiology and progression of DCM is controversial.

OBJECTIVES

Evaluation of the role of hypothyroidism in etiology and progression of DCM.

ANIMALS

A total of 175 Doberman Pinschers.

METHODS

In this longitudinal prospective study, echocardiography and 24-hour ambulatory ECG recordings were performed in all dogs as screening tests for DCM. Total thyroxine (TT4 ) and thyroid ultrasonography served as initial screening tests for hypothyroidism and low TT4 values were followed up by a thyroid stimulating hormone (TSH) test or free total thyroxine (fT4 )/cTSH measurements. Additionally, a follow-up study of dogs affected by both DCM and hypothyroidism under optimal treatment for hypothyroidism was conducted.

RESULTS

A total of 107 dogs were healthy, 45 dogs had DCM, 11 hypothyroidism, and 12 dogs had both DCM and hypothyroidism. TT4 values as well as the thyroid volumes were equivalent in the healthy dogs and in those with DCM. Neither ventricular premature complexes nor echocardiographic parameters differed between healthy and hypothyroid dogs. Dogs with DCM had a 2.26-fold (CI0.95 = 1.1-4.8) higher risk of also being affected by hypothyroidism. Despite optimal thyroid treatment of dogs with hypothyroidism and DCM, there was a progression of the heart disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study did not confirm a role of hypothyroidism in the etiology or progression of DCM. Treatment of hypothyroidism did not improve the clinical outcome.

Interactions between thyroid and kidney function in pathological conditions of these organ systems: a review

Thyroidal status affects kidney function already in the embryonic stage. Thyroid hormones influence general tissue growth as well as tubular functions, electrolyte handling and neural input. Hyper- and hypo-functioning of the thyroid influences mature kidney function indirectly by affecting the cardiovascular system and the renal blood flow, and directly by affecting glomerular filtration, electrolyte pumps, the secretory and absorptive capacity of the tubuli, and the structure of the kidney. Hyperthyroidism accelerates several physiologic processes, a fact which is reflected in the decreased systemic vascular resistance, increased cardiac output (CO), increased renal blood flow (RBF), hypertrophic and hyperplastic tubuli, and increased glomerular filtration rate (GFR). Renal failure can progress due to glomerulosclerosis, proteinuria and oxidative stress. Hypothyroidism has a more negative influence on kidney function. Peripheral vascular resistance is increased with intrarenal vasoconstriction, and CO is decreased, causing decreased RBF. The influence on the different tubular functions is modest, although the transport capacity is below normal. The GFR is decreased up to 40% in hypothyroid humans. Despite the negative influences on glomerular and tubular kidney function, a hypothyroid state has been described as beneficial in kidney disease. Kidney disease is associated with decreased thyroid hormone concentrations caused by central effects and by changes in peripheral hormone metabolism and thyroid hormone binding proteins. Geriatric cats form an animal model of disease because both hyperthyroidism and chronic kidney disease (CKD) have high prevalence among them, and the link between thyroid and kidney affects the evaluation of clinical wellbeing and the possible treatment options.

Adipsic Hypernatremia in a Dog with Antithyroid Antibodies in Cerebrospinal Fluid and Serum

A 4-year-old, male Labrador retriever, weighing 27 kg, presented with abrupt clinical signs including mental retardation, circling and head pressing. The dog never ingested water by choice. An adipsia of the dog was persisted and developed to hypernatremia with artifactual hyperchloremia. Serial endocrine results and image findings were suggestive of a hypothyroidism. The dog revealed the presence of antithyroid antibodies in the cerebrospinal fluid and serum. With the administration of levothyroxine sodium, his neurologic signs were alleviated within the first week of treatment and adipsia was also resolved.