Hyperthyroidism refers to increased production and secretion of thyroid hormone from the thyroid gland.
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Terminology
Hyperthyroidism is not synonymous with thyrotoxicosis, the latter referring to a clinical syndrome of excess thyroid hormone 1.
Clinical presentation
Hyperthyroidism may be accompanied by the signs and symptoms of thyrotoxicosis (e.g. heat intolerance, weight loss, tremor). However, it is also possible to have a subclinical form of hyperthyroidism (i.e. lacking thyrotoxicosis), but this is less common 1.
ECG
sinus tachycardia
high voltage QRS complexes
Thyrotoxicosis predisposes patients to a variety of tachydysrhythmias, as well as atrial and ventricular ectopy 2:
paroxysmal supraventricular tachycardia
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non-specific ST segment and T wave changes
elderly patients may have rate-related ischemia
premature ventricular complexes (PVCs)
Pathology
Etiology
There are numerous causes of hyperthyroidism 1:
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increased thyroid gland stimulation
TSH receptor stimulating antibodies: Graves disease (most common cause of hyperthyroidism in developed countries 5)
excess TSH secretion (e.g. TSH-secreting pituitary tumors)
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independent thyroid function
TSH receptor gene activating mutations (e.g. functioning adenoma, multinodular goiter)
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thyroid tissue inflammation and subsequent release of stored thyroid hormone
autoimmune (e.g. acute Hashimoto thyroiditis, postpartum thyroiditis)
viral (e.g De Quervain thyroiditis)
infectious (e.g. bacterial)
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iatrogenic
radiation thyroiditis
thyroid surgery
drug-induced (e.g. amiodarone, checkpoint inhibitors, alemtuzumab)
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extrathyroid source
dietary (e.g. factitious hyperthyroidism, hamburger thyrotoxicosis 4)
neoplastic (e.g. functional thyroid cancer metastases, pituitary adenoma, struma ovarii)
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iodine exposure
iatrogenic (e.g. iodine contrast, iodine-containing drugs)
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pseudohyperthyroidism
high intake of the vitamin biotin may interfere with thyroid hormone assays 3
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