Hyperthyroidism is the most common endocrine disease in cats over 8 years old, with the average age of first visit being 13 years old. Although cats aged 4 to 20 years have been affected, cases younger than 8 years old are rare.
What is feline hyperthyroidism (FHT)?
Hyperthyroidism refers to a multi-system disease caused by excessive hormone production and secretion by the thyroid gland. Hyperthyroidism in cats is generally divided into two types: unilateral and bilateral, of which bilateral disease accounts for the majority. Excessive secretion of thyroid hormone will cause cats to react like poisoning, resulting in thyroid crisis, thyrotoxic cardiomyopathy and systemic hypertension.
At present, the pathogenesis of hyperthyroidism is not very clear. It is found that immune, nutritional, genetic, infectious and environmental factors may cause hyperthyroidism.
Common Symptoms:
Clinical signs of FHT vary, with the disease affecting both the whole body and multiple systems. Because of the high prevalence of FHT, baseline serum thyroxine levels are routinely screened in middle-aged and older cats. The diagnosis of FHT is usually made in cats with vague (or absent) clinical signs.
Common clinical signs (Table 1) include weight loss, increased appetite, increased activity, vomiting, diarrhea, polyuria/polydipsia, poor grooming, and behavioral changes.
In a single case, any combination of these clinical signs may be present, with varying degrees of severity. Weight loss is the most common symptom of FHT.
Affected cats are usually in poor condition and have a slovenly appearance. Cats with FHT may show increased activity, aggression, or anxiety despite their advanced age. Poor tolerance to stress and panting are also common signs.
Uncommon Signs:
Increased activity and increased appetite are common signs of FHT, while a small percentage of cats may show hysteria, lethargy, and poor appetite. This uncommon condition is called "apathetic" hyperthyroidism.
In humans, apathetic hyperthyroidism, also known as asymptomatic hyperthyroidism, occurs primarily in older patients and is associated with concurrent illnesses and treatments that may cause lethargy and decreased appetite.
However, this condition has not been found in younger patients. The mechanism of apathetic FHT has not been established, and no association has been found between underlying illness and apathetic FHT.
Cats over 8 years old who meet the symptoms described above, especially those who are gluttonous, polydipsia, and polyuria, should be suspected of hyperthyroidism. The clinical symptoms of hyperthyroidism are not specific, and hyperthyroidism itself is associated with many other diseases, such as chronic renal failure.
Relevant examinations in the hospital may include: blood routine, urine test, biochemical test, thyroid function evaluation (TSH, fT4, TT4), X-ray, neck ultrasound, etc. Combining the results of several tests, it can be determined whether hyperthyroidism exists.
In addition, thyroid function assessment cannot accurately diagnose hyperthyroidism. There are many cats with symptoms, but the levels of hyperthyroidism tests are normal; there are also many cats without obvious symptoms, but the levels of hyperthyroidism tests are very high.
Therefore, thyroid function assessment can only be used as an auxiliary diagnostic tool, and one or more measurements can be performed.
In short, elderly cats must have regular physical examinations to detect the disease early, so that the disease can be better controlled and treated.
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