Why these diagnoses are often made late – treatment options, monitoring and side effects
The thyroid produces hormones that regulate your pet’s metabolism, growth, and many of its bodily functions. When it becomes imbalanced, this has far-reaching consequences for the entire body. In cats, we almost exclusively see hyperthyroidism, whereas dogs typically suffer from hypothyroidism. The disease often remains undetected for a long time, especially in dogs, as symptoms develop gradually and can easily be mistaken for normal aging. Cats may display slightly atypical behaviours that can make diagnosis somewhat easier.
Hyperthyroidism in Cats
Prevalence and Causes
Hyperthyroidism is the most common hormonal disorder in older cats. In most cases, a benign thyroid tumour, an adenoma, is the underlying cause. Malignant tumours are much rarer.
Typical Symptoms
• Weight loss despite increased appetite
• Restlessness, nervousness, increased vocalization
• Vomiting or diarrhea
• Rapid heartbeat, high blood pressure
• Scruffy coat, increased drinking and urination
Because many cats naturally lose weight with age, the disease is often diagnosed late. Nervousness and restlessness can be decisive for their diagnosis.
Diagnosis
• Blood tests
• Ultrasound or scintigraphy in unclear cases
Treatment Options
• Radioiodine therapy: This aims to permanently destroy overactive thyroid cells – only available at specialist clinics in Switzerland, but the best possible treatment.
• Medication: Lifelong tablets or liquid medication (e.g. methimazole).
• Surgery: Removal of affected thyroid tissue, now less common.
• Dietary therapy: Low-iodine diets may help in individual cases but are not practical for every cat.
Monitoring and Possible Side Effects
• Regular blood tests (every 4–8 weeks during the adjustment period, later every 3–6 months).
• Medication may cause side effects such as loss of appetite, vomiting, or liver issues.
• The kidneys must also be monitored, as hyperthyroidism can mask pre-existing kidney disease.
Hypothyroidism in Dogs
Prevalence and Causes
Hypothyroidism is one of the most common hormonal disorders in dogs, usually affecting middle-aged to older animals. It is typically caused by autoimmune destruction of the thyroid gland.
Typical Symptoms
• Weight gain despite normal or reduced food intake
• Lethargy, increased sleeping
• Sensitivity to cold
• Dull coat, hair loss, skin problems
• Slow heart rateMany of these symptoms develop slowly and are easily attributed to “normal aging.
Diagnosis
• Blood tests
• Repeat testing, as values may fluctuate
• Exclusion of other diseases with similar symptoms
Treatment Options
• Hormone-replacement therapy: Lifelong administration of the thyroid hormone (levothyroxine) in tablet form.
• Dosage is adjusted individually based on body weight and blood values.
Monitoring and Possible Side Effects
• Follow-up blood tests about 6–8 weeks after starting therapy, later every 6–12 months.
• Precise adherence to medication timing is essential.
Why Diagnoses Are Often Made Late
• Gradual onset: Symptoms appear over months to years.
• Confusion with aging: Weight loss in cats and weight gain in dogs, fatigue, or behavioral changes appear nonspecific.
• Individual differences: Not every dog displays all classic symptoms.
Therefore, regular blood tests in older pets are the most important measure for early detection.
Practical Tips for Owners
For Cats with Hyperthyroidism
• Administer medication at the same time every day, with or without food as advised by your cat’s veterinarian.
• Monitor weight regularly (e.g., once per week).
• Take blood-pressure checks seriously, as many cats with hyperthyroidism develop hypertension.
For Dogs with Hypothyroidism
• Give tablets at the same time every day, preferably on an empty stomach or as advised by your dog’s veterinarian.
• Document weight and energy levels – small improvements motivate and aid monitoring.
• Observe coat and skin condition – improvements often take several weeks to manifest.
• Give your dog gentle activity – exercise promotes metabolism and well-being.
Conclusion
Thyroid diseases are common in dogs and cats but are often detected late. The earlier the diagnosis, the better they can be treated to avoid secondary health issues. With consistent medication, regular monitoring, and attentive observation by owners, affected animals can enjoy a good and long life despite having a chronic condition.
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