Hypothyroidism

A patient with months of fatigue, constipation, cold intolerance, dry skin, and a slowing pulse may have hypothyroidism, but symptoms alone do not establish the diagnosis. The first useful question is whether the thyroid gland has failed or whether the pituitary–hypothalamic system is failing to stimulate it. That distinction changes how laboratory results are interpreted and how treatment is monitored. For suspected primary hypothyroidism, begin with serum TSH and add free T4 when TSH is abnormal. In Canada, this symptom-driven, TSH-first approach is preferred to routine testing of asymptomatic adults. Once hypothyroidism is confirmed, levothyroxine replacement is usually straightforward in a young, healthy adult but must be introduced cautiously in older adults, coronary disease, adrenal insufficiency, and pregnancy.