A 34 year old woman presents with a drooping left eyelid for 1 day. She also experienced difficulty in speaking, swallowing and keeping her head up. The symptoms become progressively worse during the course of the day. Close questioning reveals a history of several episodes of drooping of an eyelid with blurred vision over the past 2 years, with varying intensities. Her medical history is otherwise unremarkable, and she is not on any drugs.
anti AchR-abs: positive anti MuSK-abs: positive
There is an 18% decrement in compound muscle action potentials over time.
TSH: 0.2 mIU/L (0.3 – 3.0) FT4: 20 pmol/L (8 - 27)
The MRI of the thorax shows no mediastinal masses.