Final answer:
Exophthalmia, characterized by bulging eyes, is a sign of hyperthyroidism, especially in relation to Graves' disease, which often causes this symptom alongside others like weight loss and rapid heartbeat.
Step-by-step explanation:
Exophthalmia is indeed a sign of hyperthyroidism, particularly Graves' disease, which is the most common cause of hyperthyroidism in the United States. This condition leads to the characteristic bulging eyes, or Graves ophthalmopathy, as a result of the overproduction of thyroid hormones, usually due to the production of thyroid-stimulating immunoglobulin (TSI). Apart from exophthalmia, other symptoms indicative of hyperthyroidism include heat intolerance, rapid and irregular heartbeat, weight loss, and goiter.