Hyperthyroidism
Medicine > Endocrinology > HyperthyroidismHyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine (T4) and free triiodothyronine (T3), or both. Major causes in humans are Graves' disease (the most common reason with 70-80%), toxic thyroid adenoma, toxic multinodular goitre, and subacute thyroiditis.
Hyperthyroidism is one of the most common endocrine conditions affecting older domesticated cats. The disease has become significantly more common since the first reports of feline hyperthyroidism in the 1970s. In cats, it is almost always caused by a benign thyroid adenoma.
Signs and symptoms
Major clinical features in humans are weight loss (often accompanied by a ravenous appetite), fatigue, weakness, hyperactivity, irritability, apathy, depression, polyuria and sweating. Additionally, patients may present with a variety of symptoms such as palpitations, dyspnea, infertility, loss of libido, nausea, vomiting, and diarrhea.
Neurological manifestations are tremor, chorea, myopathy, and periodic paralysis. Stroke of cardioembolic origin due to coexisting atrial fibrillation may be mentioned as one of the most serious complications of hyperthyroidism.
In cats, rapid weight loss, rapid heart rate, vomiting, diarrhea, increased water consumption, and increased urine production are the most common symptoms.
As to other autoimmune disorders related with thyrotoxicosis, an association between thyroid disease and myasthenia gravis has well been recognised. The thyroid disease, in this condition, is often an autoimmune one and approximately 5% of patients with myasthenia gravis also have hyperthyroidism. Myasthenia gravis rarely improves after thyroid treatment and relation between two entities is yet unknown. Some very rare neurological manifestations that are reported to be dubiously associated with thyrotoxicosis are pseudotumor cerebri, amyotrophic lateral sclerosis and a Guillain-BarrÃÂé like syndrome.
Diagnosis
A diagnosis is made through a blood test, by measuring the level of T4 in the blood. High T4 levels are considered indicative of hyperthyroidism.Treatment
The major and generally accepted modalities for treatment of hyperthyroidism
in humans or cats are:
If too high a dose is used in pharmacological treatment, patients can develop symptoms of hypothyroidism. Hypothyroidism is also a very common result of surgery or radiation treatment as it is difficult to gauge how much of the thyroid gland should be removed.