Unilateral proptosis & bilateral 6th nerve palsy is seen in –
**Core Concept**
Unilateral proptosis and bilateral 6th nerve palsy are clinical manifestations of a condition that affects the orbit and the cranial nerves controlling eye movements. This condition is often associated with increased intraorbital pressure and impairment of the nerves responsible for lateral rectus muscle function.
**Why the Correct Answer is Right**
The correct answer is **D. Thyroid Ophthalmopathy**. Thyroid ophthalmopathy, also known as Graves' ophthalmopathy, is an autoimmune disorder that causes inflammation of the tissues around the eye, including the orbit and the extraocular muscles. The increased intraorbital pressure and inflammation can lead to unilateral proptosis (bulging of the eye) and bilateral 6th nerve palsy, which results from compression of the abducens nerve (cranial nerve VI) by the swollen and inflamed tissues.
**Why Each Wrong Option is Incorrect**
**Option A:** Orbital cellulitis is a bacterial infection of the orbit that can cause proptosis and eyelid swelling, but it typically does not cause bilateral 6th nerve palsy.
**Option B:** Orbital metastasis can cause proptosis, but it is less likely to cause bilateral 6th nerve palsy.
**Option C:** Orbital trauma can cause proptosis and eyelid swelling, but it is not typically associated with bilateral 6th nerve palsy.
**Clinical Pearl / High-Yield Fact**
Thyroid ophthalmopathy is a classic example of a condition where the eyes are affected by an autoimmune disorder, and it is essential to consider this diagnosis in patients with proptosis and 6th nerve palsy.
**Correct Answer: D. Thyroid Ophthalmopathy**