Feline hyperthyroidism: prevalence and risk factors
1. Prevalence of and risk factors for feline hyperthyroidism among a clinical population of cats in southern Germany. Köhler I et al. Tierarztl Prax Ausg K Kleintiere Heimtiere. 2016 Feb 23
A prospective study to determine the prevalence of and possible risk factors associated with feline hyperthyroidism in a clinical population of cats in southern Germany.
The authors studied 495 cats aged 8 years or over by measuring their serum T4 levels. The prevalence of feline hyperthyroidism was 12.3%.
The oldest cats (p < 0.001), females (p = 0.019) and mixed breeds (p = 0.016) had higher frequencies of feline hyperthyroidism.
There was a statistically significant association between hyperthyroidism and eating wet foods from aluminium cans (p < 0.13).
2. Evaluation of serum thyroid-stimulating hormone concentration as a diagnostic test for hyperthyroidism in cats. E. Peterson et al. Jour of Vet Int Med Vol 29, Issue 5, pp 1327-1334, Sept/Oct 2015
This prospective study examined the value of canine TSH as a diagnostic test of hyperthyroidism in cats.
The sample included 917 untreated hyperthyroid cats, 32 euthyroid cats with suspected hypothyroidism, and 131 clinically healthy cats. T4, T3, free T4 and canine TSH were measured and the diagnosis of hyperthyroidism confirmed by thyroid scintigraphy.
Canine TSH concentrations were suppressed in 98% of the hyperthyroid cats, with low specificity in cases of moderate hyperthyroidism.
3. Evaluation of thyroid-stimulating hormone, total thyroxine, and free thyroxine concentrations in hyperthyroid cats receiving methimazole treatment. Aldridge C et al. J Vet Intern Med 2015
This study compared the efficacy of measuring total T4, fT4ED (free T4 concentration by equilibrium dialysis) and TSH concentrations to establish thyroid function in cats receiving methimazole. The study also aimed to:
- determine the prevalence of iatrogenic hyperthyroidism.
- examine the relationship between thyroid hormones and serum creatinine levels.
A total of 125 hyperthyroid cats receiving methimazole and with total T4 concentrations of less than 4 mcg/dL were analysed. Iatrogenic hyperthyroidism was defined as a low total T4 or fT4ED concentration in conjunction with elevated TSH.
Some 33% of cats had an increase in TSH. Within the group of cats with low total T4 and fT4ED concentrations, 68% and 73% had high TSH levels.
Only 18% of cats with a normal TSH level had increased creatinine concentration, compared with 39% of those with a high TSH.
4. Thyroid scintigraphy findings in 2,096 cats with hyperthyroidism Peterson ME et al. Vet Radiol Ultrasound 2015;56: 84-95
The authors reported that 98.7% of the subjects had a thyroid/salivary gland ratio > 1.5, while 96.1% had a thyroid/background ratio > 6.1. Involvement was unilateral in 31.7%, bilateral asymmetric in 50.6% and bilateral symmetrical in 12.3% of the sample.
Ectopic thyroid disease and thyroid carcinoma were uncommon, at 4% and 2% respectively.
5. Prevalence and degree of thyroid pathology in hyperthyroid cats increases with disease duration: a cross-sectional analysis of 2,096 cats referred for radioiodine therapy Peterson ME et al. J Feline Med Surg 2015
This study compared T4 concentrations with the scintigraphy findings in cats referred for radioiodine treatment. The study sample included 2,096 cats with hyperthyroidism divided into five groups according to disease duration.
A total of 47.5% of cats received methimazole, which was discontinued at least 1 week before performing scintigraphy to measure T4 levels. The authors studied the pattern, location and size of the thyroid tumours.
They reported that the prevalence of severe hyperthyroidism, large thyroid tumours, multifocal involvement, intrathoracic thyroid masses and suspected malignant disease all increased proportionally with disease duration.
In conclusion, we can say that feline hyperthyroidism is a common disease which can be diagnosed according to the results of TSH tests and scintigraphy.
