**Question:** Stellwagg's sign of Graves disease is:

A. Inability to adduct the eyes
B. Inability to abduct the eyes
C. Inability to abduct and adduct the eyes
D. Enlargement of the extraocular muscles

**Core Concept:** Stellwagg's sign is a clinical sign associated with Graves' disease, which is a common cause of hyperthyroidism. Graves' disease is an autoimmune disorder where the immune system mistakenly attacks the thyroid gland, leading to overproduction of thyroid hormones. This overproduction can cause various symptoms and signs, including ocular manifestations.

**Why the Correct Answer is Right:** Stellwagg's sign is associated with Graves' disease due to the thyroid hormone-induced inflammation and edema of the extraocular muscles. In this condition, the affected muscles cannot fully move the eye (inability to abduct and adduct the eyes). The correct answer is **C.** Inability to abduct and adduct the eyes, as it accurately reflects the ocular manifestations of Graves' disease.

**Why Each Wrong Option is Incorrect:**

A. **Inability to adduct the eyes (Option A)**: This option is incorrect because Graves' disease primarily affects the abduction and not the adduction of the eyes. Stellwagg's sign involves the extraocular muscles' swelling, leading to the inability to abduct (move outward) and adduct (move inward) the eyes.

B. **Inability to abduct the eyes (Option B)**: This option is incorrect for the same reason as Option A. Graves' disease primarily affects the extraocular muscles' abduction, not abduction.

C. **Inability to abduct and adduct the eyes (Option C)**: This option is correct but duplicates the correct answer (C), which explains the clinical sign better.

D. **Enlargement of the extraocular muscles (Option D)**: While the extraocular muscles can enlarge due to Graves' disease, this option does not specifically address the clinical sign of Stellwagg's sign. Instead, this option discusses a potential consequence of the disease in the context of ocular symptoms.

**Stellwagg's sign in Graves' disease is a clinical sign reflecting the ocular manifestations of the condition. It occurs due to the autoimmune process causing inflammation and edema of the extraocular muscles, leading to difficulty in moving the eyes outward (abduction) and inward (adduction). The sign is named after Dr. Wilhelm Stellwagg, who first described it in 1893. This clinical sign helps differentiate Graves' disease from other causes of thyroid eye disease.