Hyperthyroidism
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Hyperthyroidism (thyrotoxicosis or "fast thyroid gland") is the clinical syndrome caused by an excess of circulating free thyroxine (T4) or free triiodothyronine (T3), or both. Major causes in humans are Graves' disease (the most common etiology with 70-80%), toxic thyroid adenoma, toxic multinodular goitre, and subacute thyroiditis.
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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 and arrhythmias (notably atrial fibrillation), dyspnea, infertility, loss of libido, nausea, vomiting, and diarrhea. In the elderly , these classical symptoms may not be present and they may present only with fatigue and weight loss leading to apathetic hyperthyroidism
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.
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-Barré 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. If the index of suspicion is low, many doctors prefer to measure thyroid-stimulating hormone (TSH). If TSH is suppressed, there may be uncontrolled production of T4, while a normal TSH generally rules out thyroid disease. Measuring specific antibodies, such as anti-TSH-receptor antibodies in Graves' disease, may contribute to the diagnosis. Additionally, scintigraphy may be required.
Treatment
The major and generally accepted modalities for treatment of hyperthyroidism in humans are:
Surgery (to remove the whole thyroid or a part of it) is not extensively used because most common forms of hyperthyroidism are quite effectively treated by the radioactive iodine method. However, some Graves' disease patients who cannot tolerate medicines for one reason or another or patients who refuse radioiodine opt for surgical intervention. The procedure is relatively safe - some surgeons are even treating partial thyroidectomy on an out-patient basis.
Radioactive iodine is given orally (either by pill or liquid) on a one-time basis to ablate a hyperactive gland. The iodine given for ablative treatment is different from the iodine used in a scan. Radioactive iodine is given after a routine iodine scan, and uptake of the iodine is determined to confirm hyperthyroidism. The radioactive iodine is picked up by the active cells in the thyroid and destroys them. Since iodine is only picked up by thyroid cells, the destruction is local, and there are no widespread side effects with this therapy. Radioactive iodine ablation has been safely used for over 50 years, and the only major reasons for not using it are pregnancy and breast-feeding.
Often, due to the difficulty of picking the correct dose, the treatment results in an opposite condition - hypothyroidism. However, that is usually easily treated by the administration of levothyroxine, which is a pure synthetic form of T4.
- thyrostatics - drugs that inhibit the production of thyroid hormones, such as methimazole (Tapazole®)
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. Supplementation with levothyroxine may be required in these cases.
In animals
In veterinary medicine, 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.
The most common presenting symptoms are: rapid weight loss, rapid heart rate, vomiting, diarrhea, increased water consumption and increased urine production.
Surgery is not normally an option in feline hyperthyroidism. Radioiodine treatment or methimazole may be used to control symptoms.
See also
de:Hyperthyreose nl:hyperthyreoïdie
External Links
Hyperthyroidism Primer (http://www.mediprimer.com/Endocrinology/hyperthyroidism/)