A solitary, autonomously functioning thyroid nodule is referred to as toxic adenoma. Most cases are cause by somatic activating mutations of the TSH receptor. Thyrotoxicosis is typically mild. A thyroid scan provides a definitive diagnostic test, demonstrating focal uptake in the hyperfunctioning nodule and diminished uptake in the remainder of the gland, as activity of the normal thyroid is suppressed. Radioiodine ablation with relatively large doses (e.g., 10-29.9 mCi ¹³¹I) is usually the treatment of choice.