to help with the diagnosis, particularly if a nodule is suspected. Thyroid diseases are highly prevalent worldwide, and treatment varies based on the disorder. Levothyroxine is the mainstay of treatment for people with hypothyroidism, while people with hyperthyroidism caused by Graves' disease can be managed with iodine therapy, antithyroid medication, or surgical removal of the thyroid gland. Thyroid surgery may also be performed to remove a thyroid nodule or to reduce the size of a goiter if it obstructs nearby structures or for cosmetic reasons. Signs and symptoms Symptoms of the condition vary with type: hypo- vs. hyperthyroidism, which are further described below. Possible symptoms of hypothyroidism are: Possible symptoms of hyperthyroidism are:Note: certain symptoms and physical changes can be seen in both hypothyroidism and hyperthyroidism —fatigue, fine / thinning hair, menstrual cycle irregularities, muscle weakness / aches (myalgia), and different forms of myxedema. Diseases Low function Hypothyroidism is a state in which the body is not producing enough thyroid hormones, or is not able to respond to / utilize existing thyroid hormones properly. The main categories are: Thyroiditis: an inflammation of the thyroid gland Hashimoto's thyroiditis / Hashimoto's disease Ord's thyroiditis Postpartum thyroiditis Silent thyroiditis Acute thyroiditis Riedel's thyroiditis (the majority of cases do not affect thyroid function, but approximately 30% of cases lead to hypothyroidism) Iatrogenic hypothyroidism Postoperative hypothyroidism Medication- or radiation-induced hypothyroidism Thyroid hormone resistance Euthyroid sick syndrome Congenital hypothyroidism: a deficiency of thyroid hormone from birth, which untreated can lead to cretinism High function Hyperthyroidism is a state in which the body is producing too much thyroid hormone. The main hyperthyroid conditions are: Graves' disease Toxic thyroid nodule Thyroid storm Toxic nodular struma (Plummer's disease) Hashitoxicosis: transient hyperthyroidism that can occur in Hashimoto's thyroiditis Structural abnormalities Goiter: an abnormal enlargement of the thyroid gland Endemic goiter Diffuse goiter Multinodular goiter Lingual thyroid Thyroglossal duct cyst Tumors Thyroid adenoma: benign / non-cancerous tumor Thyroid cancer Papillary Follicular Medullary Anaplastic Lymphomas and metastasis from elsewhere (rare) Medication side effects Certain medications can have the unintended side effect of affecting thyroid function. While some medications can lead to significant hypothyroidism or hyperthyroidism and those at risk will need to be carefully monitored, some medications may affect thyroid hormone lab tests without causing any symptoms or clinical changes, and may not require treatment. The following medications have been linked to various forms of thyroid disease: Amiodarone (more commonly can lead