A 44-year-old woman presents to the clinic with complaints of extreme fatigue, weight gain, decreased appetite, cold intolerance, dry skin, hair loss, and sleepiness. She also admits that she often bursts into tears without any reason and has been exceptionally forgetful. Her vision is occasionally blurry, and she admits to being depressed without any social or occupational triggers. Past medical history noncontributory. Physical exam Temp 96.2˚F, pulse 62 and regular, BP 108/90, respirations. Dull facial expression with coarse facial features. Periorbital puffiness noted. Based on the clinical history and physical exam, and pending laboratory data, the ARNP diagnoses the patient with hypothyroidism.
What causes hypothyroidism?