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12-27-2008, 08:41 AM
Hyperthyroidism (or"overactive thyroid gland") is the clinical syndrome caused by an excess of circulating free thyroxine (T4) or free triiodothyronine (T3), or both.[edit] Signs and symptomsMajor clinical features in humans are weight loss (often accompanied by a ravenous appetite), Intolerance to heat, 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, 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 hyperthyroidismNeurological 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 been well 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-BarrΓ©-like syndrome.Minor ocular signs, which may be present in any type of hyperthyroidism, are eyelid retraction ("stare") and lid-lag. These"fear-like"eye-signs result from thyroid hormone's exacerbation of the action of norepinephrine. In hyperthyroid stare (Dalrymple sign) the eyelids are retracted upward more than normal (the normal position is at the superior corneoscleral limbus, where the"white"of the eye begins at the upper border of the iris). In lid-lag (von Graefe's sign), when the patient tracks an object downward with their eyes, the eyelid fails to follow the downward moving iris, and the same type of upper globe exposure which is seen with lid retraction occurs, temporarily. These signs disappear with treatment of the hyperthyroidism, or treatment by certain anti-adrenergic drugs.Neither of these ocular signs should be confused with exopthalmos (protrusion of the eyeball) which occurs in one thyroid-related disease (Grave's disease), but which is not caused by the hyperthyroid state in that disease, and is unrelated to it. Exopthalmos when present may exacerbate these signs, however.[edit] DiagnosisA diagnosis is suspected through blood tests, by measuring the level of thyroid-stimulating hormone (TSH) in the blood. A low TSH indicates increased production of T4 and/or T3. Measuring specific antibodies, such as anti-TSH-receptor antibodies in Graves'disease, may contribute to the diagnosis. In all patients with hyperthyroxinemia, scintigraphy is required in order to distinguish true hyperthyroidism from thyroiditis.TreatmentThe major and generally accepted modalities for treatment of hyperthyroidism in humans are:[edit] SurgerySurgery (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. Also, some surgeons believe that radioiodine treatment is unsafe in patients with unusually large gland, or those whose eyes have begun to bulge from their sockets, claiming that the massive dose of iodine needed will only exacerbate the patient's symptoms. The procedure is quite safe - some surgeons even perform partial thyroidectomies on an out-patient basis.RadioiodineIn Radioiodine (treatment) therapy, radioactive iodine is given orally (either by pill or liquid) on a one-time basis to destroy the function of 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.
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