A 60-year-old woman being investigated for menorrhagia is found on history to have lethargy, constipation, cold intolerance, and muscle stiffness. Which of the following is the most likely diagnosis?

Later symptoms of hypothyroidism include loss of intellectual and motor activity, declining appetite, dry hair and skin, and deepening voice. In the elderly, hypothyroidism can be misdiagnosed as due to aging or to other diseases such as Parkinson disease, Alzheimer disease, or depression.