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Long-term mild excess of thyroid hormone can thus cause impaired cardiac reserve and exercise capacity. [4] In a large population-based study of 2008, the odds of having poorer cognitive function were greater for sub-clinical hyperthyroidism than for stroke , diabetes mellitus , and Parkinson's disease . [ 48 ]
Graves' disease is the cause of about 50% to 80% of the cases of hyperthyroidism in the United States. [1] [7] Other causes include multinodular goiter, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. [1] [2] A less common cause is a pituitary adenoma. [1]
Myxedema is more common in women than in men. [3] Myxedema can occur in: Hyperthyroidism, associated with pretibial myxedema and exophthalmos. Pretibial myxedema can occur in 1–4% of patients with Graves' disease, a cause of hyperthyroidism. [4] Hypothyroidism, including Hashimoto's thyroiditis. [5]
To understand how high levels of thyroxine can be toxic and lead to thyrotoxic myopathy physiologically, consider basic neuromuscular junction function. Under normal circumstances, muscle contraction occurs when electrical impulses travel down descending axons from the brain or spinal cord towards the neuromuscular junction .
The doctor can look for potential underlying causes, including dementia, medication effects, or environmental factors, Elhelou says. From there, they can suggest effective ways to help you manage ...
Stimulating antibodies to the TSH receptor mimic TSH and cause Graves' disease. In addition, hCG shows some cross-reactivity to the TSH receptor and therefore can stimulate production of thyroid hormones. In pregnancy, prolonged high concentrations of hCG can produce a transient condition termed gestational hyperthyroidism. [14]
Free T4 and total T3 can be measured when hyperthyroidism is of high suspicion as it will improve the accuracy of the diagnosis. Free T4, total T3 or both are elevated and serum TSH is below normal in hyperthyroidism. If the hyperthyroidism is mild, only serum T3 may be elevated and serum TSH can be low or may not be detected in the blood. [14]
Myxedema coma is an extreme or decompensated form of hypothyroidism and while uncommon, is potentially lethal. [1] [2] [3] A person may have laboratory values identical to a "normal" hypothyroid state, but a stressful event (such as an infection, myocardial infarction, or stroke) precipitates the myxedema coma state, usually in the elderly.