Snapshot A 32-year-old woman presents to the clinic complaining of fatigue and weight gain for the past 2 months. She endorses cold intolerance, constipation, and dry skin but denies fever, diarrhea, swelling, chest pain, or shortness of breath. A physical examination demonstrates a lethargic, stocky patient with brittle hair. Her past medical history is significant for asthma that is well controlled with her rescue inhaler. Her laboratory studies demonstrate elevated levels of thyroid stimulating hormone. (Hashimoto thyroiditis) Hypothyroidism Clinical definition disorder characterized by the under production of thyroid hormone Epidemiology Demographics iodine deficiency is the most common cause of hypothyroidism worldwide Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas ETIOLOGY Pathogenesis primarily due to thyroid disease (primary hypothyroidism) but can be caused by secondary and/or tertiary hypothyroidism primary hypothyroidism Hashimoto thyroiditis (chronic autoimmune thyroiditis) login to view 1 more bullet infiltrative disease (e.g., fibrous thyroiditis) iatrogenic disease login to view 3 more bullets iodine deficiency and/or excess thyroid hormone resistance login to view 2 more bullets medications login to view 6 more bullets secondary and tertiary hypothyroidism secondary hypothyroidism login to view 3 more bullets tertiary hypothyroidism login to view 1 more bullet Hyperthyroidism Clinical definition disorder defined by the over activity of the thyroid leading to excess thyroxine, leading to an acceleration of the body’s metabolism Epidemiology Demographics more common in women than men (5:1 ratio) Grave disease is the most common cause of hyperthyroidism ETIOLOGY Pathogenesis increased synthesis of thyroxine or from the release of preformed hormone secondary to inflammation or destruction of thyroid tissue causing a low TSH increased de novo synthesis of thyroxine Grave disease login to view 2 more bullets toxic adenoma/toxic multinodular goiter login to view 2 more bullets trophoblastic disease/germ cell tumors login to view 1 more bullet ectopic TSH secretion login to view 1 more bullet release of preformed hormone thyroiditis login to view 1 more bullet exogenous ingestion ectopic production of thyroid hormone login to view 1 more bullet Presentation Hypothyroidism Hyperthyroidism Cold intolerance (↓ heat production) Heat intolerance (↑ heat production) Weight gain and ↓ appetite Weight loss and ↑ appetite Hypoactivity, lethargy, fatigue, and weakness Hyperactivity Constipation Diarrhea ↓ Reflexes ↑ Reflexes Bradycardia Tachycardia, palpitations, arrhythmias Dry, cool skin and coarse, brittle hair Warm, moist skin and fine hair Diastolic hypertension Systolic hypertension Myxedema (facial/periorbital) Osteoporosis and hypercalcemia "Myxedema madness": syndrome characterized by psychosis, confusion, and disorientation Apathetic thyrotoxicosis Studies Diagnostic testing diagnostic approach diagnosis is based on clinical suspicion and confirmed via thyroid function tests Labs Hypothyroidism Hyperthyroidism ↑ TSH (best first test) ↓ TSH (best first test) ↓ Total T4 ↑ Total T4 ↓ Free T4 ↑ Free T4 Hypercholesterolemia (↓ LDL receptor synthesis) Hypocholesterolemia (↑ LDL receptor synthesis) Treatment Hypothyroidism Hyperthyroidism Levothyroxine Dose should be increased during pregnancy due to increased TBG Thionamides (e.g.,methimazole) Ablative131I therapy Propranolol (rate/symptom control) Complications Myxedema coma (hypothyroidism) Thyroid storm (hyperthyroidism)