Hyperthyroidism

Hyperthyroidism is the clinical syndrome caused by an excess of circulating free thyroxine or free triiodothyronine, or both.

Major causes in humans are: Graves' disease, Toxic thyroid adenoma and Toxic multinodular goitre.  Excess thyroid hormone from pills can also cause hyperthyroidism. Amiodarone, a heart medication, can sometimes cause hyperthyroidism.

Other causes of hyperthyroxinemia are not to be confused with true hyperthyroidism and include subacute and other forms of thyroiditis. Thyrotoxicosis can occur in both hyperthyroidism and thyroiditis. When it causes acutely increased metabolism, it is sometimes called "thyroid storm".

Major clinical weight loss, 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, shortness of breath, 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 been well recognized. 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.

Minor ocular signs, which may be present in any type of hyperthyroidism, are eyelid retraction and lid-lag. These "fear-like" eye-signs result from thyroid hormone's exacerbation of the action of norepinephrine. In hyperthyroid stare the eyelids are retracted upward more than normal. In lid-lag, 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 which occurs in one thyroid-related 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.

The major and generally accepted modalities for treatment of hyperthyroidism in humans are: surgery, radioiodine, thyrostatics, and beta-blockers. 

...More at Wikipedia

Related Links:

• US National Library of Medicine
• Mayo Clinic

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