Hyperthyroidism vs. Thyrotoxicosis
The term hyperthyroidism refers to an inappropriately elevated thyroid function. The term thyrotoxicosis refers to an excessive amount of circulating thyroid hormones from any source. Increased levels of thyroid hormones can occur in the setting of an otherwise normal thyroid function. For example, when there is inappropriate exogenous thyroid hormone or excessive release of stored hormone from an inflamed thyroid gland.
Though often used interchangeably, thyrotoxicosis and hyperthyroidism are NOT synonymous.
Thyroid Storm (thyroid crisis)
Thyroid storm happens when the thyroid gland suddenly releases large amounts of thyroid hormone in a short period of time. Thyroid storm is a potentially fatal complication in people who already have hyperthyroidism. Thyroid storms typically occur in people with untreated or partially treated thyrotoxicosis who then experience a precipitating event such as surgery, infection, or trauma that causes their thyroid gland to release a “storm” of thyroid hormones into blood streams in a short amount of time. E.g. people with untreated or undertreated graves disease are at risk of a thyroid storm.
You have to identify a thyroid storm and initiate treatment quickly, even before labs return.
Resources:
http://emedicine.medscape.com/article/767130-overview
http://www.webmd.com/women/tc/thyroid-storm-topic-overview