The common symptoms of an overactive thyroid are weight loss, increased appetite, irritability, rapid heart rate and anxiety, according to the Office on Women's Health, whereas underactive thyroid symptoms include weight gain, cold sensitivity, fatigue, depression and muscle weakness. Thyroid cancer is often asymptomatic, but it may cause trouble swallowing or hoarseness.
Hyperthyroidism is the name given to an overactive thyroid, while hypothyroidism is the medical term for an underactive thyroid, as the Office on Women's Health explains. Most cases of hyperthyroidism are due to Grave's disease, an autoimmune condition that causes the immune system to stimulate the thyroid gland to produce excessive amounts of thyroid hormones. Thyroid nodules also sometimes cause the thyroid gland to produce more hormones than the body needs. Hypothyroidism is most often the result of an autoimmune condition called Hashimoto's disease, which causes the patient's body to attack the thyroid gland, but hypothroidism can also result from hyperthyroidism treatment, thyroid removal, pituitary problems and radiation treatment for cancer.
Patients with hyperthyroidism are at an increased risk of osteoarthritis, according to the Office on Women's Health, while hypothyroidism patients sometimes have an increased risk of heart disease due to high levels of LDL cholesterol in the blood. Tests for thyroid problems include blood tests, imaging scans, radioactive iodine uptake tests, ultrasound imaging and fine-needle biopsy. A commonly performed blood test measures levels of thyroid-stimulating hormone, or TSH.