Although most thyroid nodules are benign, they sometimes can cause serious complications. Large nodules or a multinodular goiter can interfere with swallowing or breathing. More serious problems occur when a nodule or goiter produces thyroid hormone, leading to hyperthyroidism.

In addition to signs and symptoms such as unintended weight loss, muscle weakness, heat intolerance, and anxiousness or irritability, hyperthyroidism can also cause the following:

• Heart-related complications. These include a rapid heart rate, atrial fibrillation (a heart rhythm disorder) and congestive heart failure ¡ª a condition in which your heart becomes too weak to circulate enough blood to meet the needs of your body.
• Weak, brittle bones (osteoporosis). The strength of your bones depends, in part, on the amount of calcium and other minerals they contain. Too much thyroid hormone interferes with your body's ability to incorporate calcium into your bones. In fact, hyperthyroidism often affects your bones before you have any other signs or symptoms of the disorder. This is especially true of postmenopausal women who are already at high risk of osteoporosis.
• Thyrotoxic crisis. This is a sudden and potentially life-threatening intensification of your signs and symptoms that requires immediate medical care.