In Graves' (thyroid-related) orbitopathy, the MOST commonly enlarged extraocular muscle on CT/MRI of the orbits is:
- A Lateral rectus
- B Inferior rectus ✓
- C Superior rectus
- D Medial rectus
Correct answer: B. Inferior rectus
Explanation
In thyroid-related orbitopathy, the order of extraocular muscle involvement by frequency is: inferior rectus > medial rectus > superior rectus > lateral rectus (mnemonic: I'M SLow). Inferior rectus enlargement causes limitation of upgaze and is the most common reason for restrictive vertical diplopia in TRO. Imaging characteristically shows spindle-shaped muscle belly enlargement with tendon sparing, distinguishing it from orbital myositis where tendons are involved.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.