What is the main clinical feature of hyperthyroidism?

The main clinical feature of hyperthyroidism is a rapid heartbeat, also known as tachycardia. Hyperthyroidism occurs when the thyroid gland produces an excessive amount of thyroid hormones, which can significantly increase the metabolic rate of the body. As a result, one of the most common cardiovascular manifestations is an increase in heart rate. This can lead to palpitations and may also be accompanied by other symptoms such as nervousness, anxiety, and increased perspiration.

In contrast, weight gain and fatigue are generally more associated with hypothyroidism, where a lack of thyroid hormone results in a slowed metabolism. Cold intolerance is likewise more characteristic of hypothyroidism, as the body's ability to generate heat is impaired. Thus, the presence of tachycardia in hyperthyroidism is a crucial distinguishing feature that helps clinicians identify and manage this condition effectively.