endocrine and metabolic disorders
Hypothyroidism
Key Points
Primary hypothyroidism is most common; it is due to disease in the thyroid, and thyroid-stimulating hormone (TSH) levels are high. Secondary hypothyroidism is less common; it is due to pituitary or hypothalamic disease, and TSH levels are low. Symptoms develop insidiously and typically include cold intolerance, constipation, and cognitive and/or personality changes; later, the face becomes puffy and the facial expression dull. Free thyroxine (T4) level is always low, but triiodothyronine (T3) may remain normal early in some disorders. Serum TSH is the best diagnostic test. Oral T4 (levothyroxine) is the preferred treatment and is given in the lowest dose that restores serum TSH levels to the midnormal range. Myxedema coma is a life-threatening complication that requires rapid diagnosis and treatment. 