Final answer:
The primary symptom of myxedema, a condition related to hypothyroidism, is cold intolerance. It involves various symptoms including a slowed metabolism and a sensitivity to cold, unlike hyperthyroidism, which has opposite effects like increased sweating and heart rate.
Step-by-step explanation:
The primary symptom of myxedema, a complex disorder associated with hypothyroidism, is cold intolerance. Myxedema is characterized by several symptoms, including the thickening of skin, weight gain, reduced mental activity, and a high sensitivity to cold. This condition is a result of an underactive thyroid gland which slows down the body's metabolic processes. Unlike hyperthyroidism, which leads to symptoms like weight loss, profuse sweating, and increased heart rate, hypothyroidism's reduced thyroid hormone levels lead to a decreased metabolic rate and an inability to tolerate cold temperatures.