MRCP2-1645
A 42-year-old woman visits her primary care physician (PCP) complaining of occasional double vision when looking upwards. She experiences diplopia, most noticeable when looking to the right and looking downwards. Upon examination, she has mild bilateral proptosis and her eyes appear normal when looking straight ahead. Her pupils are equal and have normal direct and consensual light reflexes. She is able to look up and down for 10 seconds without any signs of fatigue. There is no weakness or fatigability in any peripheral muscles.
The following investigations were conducted:
Free Thyroxine FT4 16 pmol/l 11–22 pmol/l
Thyroid Stimulating Hormone (TSH) 2.8 µU/l 0.17–3.2 µU/l
What is the most probable diagnosis?