Which endocrine disease is associated with exophthalmos?

Exophthalmos, or the protrusion of the eyeball, is commonly associated with hyperthyroidism, particularly in the context of Graves' disease, an autoimmune thyroid condition. In hyperthyroidism, the overproduction of thyroid hormones leads to an increase in metabolism, which can stimulate the accumulation of glycosaminoglycans (GAGs) behind the eyes. This accumulation causes the eyes to bulge forward. The condition is a characteristic manifestation of Graves' disease and serves as a key clinical indicator for diagnosing hyperthyroid conditions, distinguishing it from other endocrine disorders.

In contrast, the other options—hypothyroidism, Cushing syndrome, and Addison's disease—do not typically present with exophthalmos. Hypothyroidism often leads to features such as weight gain and lethargy but not eye protrusion. Cushing syndrome, characterized by excess cortisol, may lead to distinct features like obesity and hypertension, while Addison's disease, which involves adrenal insufficiency, usually presents with symptoms such as fatigue, weight loss, and hyperpigmentation but lacks ocular manifestations such as exophthalmos. Therefore, hyperthyroidism is the condition that is most directly associated with the symptom of exophthalmos.