Which symptom is commonly associated with Graves' disease?

Protruding eyes, or exophthalmos, is a hallmark symptom associated with Graves' disease, which is an autoimmune disorder that causes hyperthyroidism. This condition leads to an overproduction of thyroid hormones, which can cause various symptoms, including increased metabolism. The eyes protrude due to inflammation and swelling of the eye muscles and surrounding tissue, which is often caused by the accumulation of glycosaminoglycans and the action of immune cells. This symptom is significant because it also highlights the connection between Graves' disease and thyroid-associated ophthalmopathy, a complication that can affect vision if not properly managed.

In contrast, weight gain is often associated with hypothyroidism rather than hyperthyroidism like in Graves' disease. Brittle nails can be a sign of various conditions but are not specific to Graves' disease. Constipation is typically linked to decreased metabolic activity seen in hypothyroidism, rather than the increased metabolism associated with Graves' disease. Therefore, protruding eyes stand out as a defining physical manifestation of this particular thyroid disorder.